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Muchun SongandAndrew Morton 0a98e13963 mm: lru: add VM_WARN_ON_ONCE_FOLIO to lru maintenance helpers 
We must ensure the folio is deleted from or added to the correct lruvec
list.  So, add VM_WARN_ON_ONCE_FOLIO() to catch invalid users.  The
VM_BUG_ON_PAGE() in move_pages_to_lru() can be removed as
add_page_to_lru_list() will perform the necessary check.

Link: https://lore.kernel.org/2c90fc006d9d730331a3caeef96f7e5dabe2036d.1772711148.git.zhengqi.arch@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Allen Pais <apais@linux.microsoft.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Chen Ridong <chenridong@huawei.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Imran Khan <imran.f.khan@oracle.com>
Cc: Kamalesh Babulal <kamalesh.babulal@oracle.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <Liam.Howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yosry Ahmed <yosry@kernel.org>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-18 00:10:47 -07:00
Ye LiuandAndrew Morton 54fdcbfe1c mm: remove unused page_is_file_lru() function 
The page_is_file_lru() wrapper function is no longer used.  The kernel has
moved to folio-based APIs, and all callers should use folio_is_file_lru()
instead.

Remove the obsolete page-based wrapper function.

Link: https://lkml.kernel.org/r/20260323090305.798057-1-ye.liu@linux.dev
Signed-off-by: Ye Liu <liuye@kylinos.cn>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-05 13:53:36 -07:00
Leno HouandAndrew Morton a6a8c087dc mm/mglru: fix cgroup OOM during MGLRU state switching 
When the Multi-Gen LRU (MGLRU) state is toggled dynamically, a race
condition exists between the state switching and the memory reclaim path. 
This can lead to unexpected cgroup OOM kills, even when plenty of
reclaimable memory is available.

Problem Description
==================
The issue arises from a "reclaim vacuum" during the transition.

1. When disabling MGLRU, lru_gen_change_state() sets lrugen->enabled to
   false before the pages are drained from MGLRU lists back to traditional
   LRU lists.
2. Concurrent reclaimers in shrink_lruvec() see lrugen->enabled as false
   and skip the MGLRU path.
3. However, these pages might not have reached the traditional LRU lists
   yet, or the changes are not yet visible to all CPUs due to a lack
   of synchronization.
4. get_scan_count() subsequently finds traditional LRU lists empty,
   concludes there is no reclaimable memory, and triggers an OOM kill.

A similar race can occur during enablement, where the reclaimer sees the
new state but the MGLRU lists haven't been populated via fill_evictable()
yet.

Solution
========
Introduce a 'switching' state (`lru_switch`) to bridge the transition.
When transitioning, the system enters this intermediate state where
the reclaimer is forced to attempt both MGLRU and traditional reclaim
paths sequentially. This ensures that folios remain visible to at least
one reclaim mechanism until the transition is fully materialized across
all CPUs.

Race & Mitigation
================
A race window exists between checking the 'draining' state and performing
the actual list operations. For instance, a reclaimer might observe the
draining state as false just before it changes, leading to a suboptimal
reclaim path decision.

However, this impact is effectively mitigated by the kernel's reclaim
retry mechanism (e.g., in do_try_to_free_pages). If a reclaimer pass fails
to find eligible folios due to a state transition race, subsequent retries
in the loop will observe the updated state and correctly direct the scan
to the appropriate LRU lists. This ensures the transient inconsistency
does not escalate into a terminal OOM kill.

This effectively reduce the race window that previously triggered OOMs
under high memory pressure.

This fix has been verified on v7.0.0-rc1; dynamic toggling of MGLRU
functions correctly without triggering unexpected OOM kills.

Link: https://lkml.kernel.org/r/20260319-b4-switch-mglru-v2-v5-1-8898491e5f17@gmail.com
Signed-off-by: Leno Hou <lenohou@gmail.com>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Jialing Wang <wjl.linux@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Bingfang Guo <bfguo@icloud.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-05 13:53:33 -07:00
Chunyan ZhangandAndrew Morton f59c0924d6 mm: userfaultfd: add pgtable_supports_uffd_wp() 
Some platforms can customize the PTE/PMD entry uffd-wp bit making it
unavailable even if the architecture provides the resource.  This patch
adds a macro API pgtable_supports_uffd_wp() that allows architectures to
define their specific implementations to check if the uffd-wp bit is
available on which device the kernel is running.

Also this patch is removing "ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP" and
"ifdef CONFIG_PTE_MARKER_UFFD_WP" in favor of pgtable_supports_uffd_wp()
and uffd_supports_wp_marker() checks respectively that default to
IS_ENABLED(CONFIG_HAVE_ARCH_USERFAULTFD_WP) and
"IS_ENABLED(CONFIG_HAVE_ARCH_USERFAULTFD_WP) &&
IS_ENABLED(CONFIG_PTE_MARKER_UFFD_WP)" if not overridden by the
architecture, no change in behavior is expected.

Link: https://lkml.kernel.org/r/20251113072806.795029-3-zhangchunyan@iscas.ac.cn
Signed-off-by: Chunyan Zhang <zhangchunyan@iscas.ac.cn>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Alexandre Ghiti <alexghiti@rivosinc.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Jones <ajones@ventanamicro.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Conor Dooley <conor.dooley@microchip.com>
Cc: Conor Dooley <conor@kernel.org>
Cc: Deepak Gupta <debug@rivosinc.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-11-24 15:08:54 -08:00
Shakeel ButtandAndrew Morton 5b3eb779a2 memcg: remove __mod_lruvec_state 
__mod_lruvec_state() is already safe against irqs, so there is no need to
have a separate interface (i.e.  mod_lruvec_state) which wraps calls to it
with irq disabling and reenabling.  Let's rename __mod_lruvec_state() to
mod_lruvec_state().

Link: https://lkml.kernel.org/r/20251110232008.1352063-4-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-11-24 15:08:54 -08:00
Lorenzo StoakesandAndrew Morton 68aa2fdbf5 mm: introduce leaf entry type and use to simplify leaf entry logic 
The kernel maintains leaf page table entries which contain either:

The kernel maintains leaf page table entries which contain either:

 - Nothing ('none' entries)
 - Present entries*
 - Everything else that will cause a fault which the kernel handles

* Present entries are either entries the hardware can navigate without page
  fault or special cases like NUMA hint protnone or PMD with cleared
  present bit which contain hardware-valid entries modulo the present bit.

In the 'everything else' group we include swap entries, but we also
include a number of other things such as migration entries, device private
entries and marker entries.

Unfortunately this 'everything else' group expresses everything through a
swp_entry_t type, and these entries are referred to swap entries even
though they may well not contain a...  swap entry.

This is compounded by the rather mind-boggling concept of a non-swap swap
entry (checked via non_swap_entry()) and the means by which we twist and
turn to satisfy this.

This patch lays the foundation for reducing this confusion.

We refer to 'everything else' as a 'software-define leaf entry' or
'softleaf'.  for short And in fact we scoop up the 'none' entries into
this concept also so we are left with:

- Present entries.
- Softleaf entries (which may be empty).

This allows for radical simplification across the board - one can simply
convert any leaf page table entry to a leaf entry via softleaf_from_pte().

If the entry is present, we return an empty leaf entry, so it is assumed
the caller is aware that they must differentiate between the two
categories of page table entries, checking for the former via
pte_present().

As a result, we can eliminate a number of places where we would otherwise
need to use predicates to see if we can proceed with leaf page table entry
conversion and instead just go ahead and do it unconditionally.

We do so where we can, adjusting surrounding logic as necessary to
integrate the new softleaf_t logic as far as seems reasonable at this
stage.

We typedef swp_entry_t to softleaf_t for the time being until the
conversion can be complete, meaning everything remains compatible
regardless of which type is used.  We will eventually remove swp_entry_t
when the conversion is complete.

We introduce a new header file to keep things clear - leafops.h - this
imports swapops.h so can direct replace swapops imports without issue, and
we do so in all the files that require it.

Additionally, add new leafops.h file to core mm maintainers entry.

Link: https://lkml.kernel.org/r/c879383aac77d96a03e4d38f7daba893cd35fc76.1762812360.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Chris Li <chrisl@kernel.org>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mathew Brost <matthew.brost@intel.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Wei Xu <weixugc@google.com>
Cc: xu xin <xu.xin16@zte.com.cn>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-11-24 15:08:50 -08:00
Li ZheandAlex Williamson 929bf010e0 mm: introduce num_pages_contiguous() 
Let's add a simple helper for determining the number of contiguous pages
that represent contiguous PFNs.

In an ideal world, this helper would be simpler or not even required.
Unfortunately, on some configs we still have to maintain (SPARSEMEM
without VMEMMAP), the memmap is allocated per memory section, and we might
run into weird corner cases of false positives when blindly testing for
contiguous pages only.

One example of such false positives would be a memory section-sized hole
that does not have a memmap. The surrounding memory sections might get
"struct pages" that are contiguous, but the PFNs are actually not.

This helper will, for example, be useful for determining contiguous PFNs
in a GUP result, to batch further operations across returned "struct
page"s. VFIO will utilize this interface to accelerate the VFIO DMA map
process.

Implementation based on Linus' suggestions to avoid new usage of
nth_page() where avoidable.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
Signed-off-by: Li Zhe <lizhe.67@bytedance.com>
Co-developed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20250814064714.56485-2-lizhe.67@bytedance.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
 2025-10-06 11:21:26 -06:00
Max KellermannandAndrew Morton f346a9473a mm: constify various inline functions for improved const-correctness 
We select certain test functions plus folio_migrate_refs() from
mm_inline.h which either invoke each other, functions that are already
const-ified, or no further functions.

It is therefore relatively trivial to const-ify them, which provides a
basis for further const-ification further up the call stack.

One exception is the function folio_migrate_refs() which does write to the
"new" folio pointer; there, only the "old" folio pointer is being
constified; only its "flags" field is read, but nothing written.

Link: https://lkml.kernel.org/r/20250901205021.3573313-11-max.kellermann@ionos.com
Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
Reviewed-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christian Zankel <chris@zankel.net>
Cc: David Rientjes <rientjes@google.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Helge Deller <deller@gmx.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Bottomley <james.bottomley@HansenPartnership.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jocelyn Falempe <jfalempe@redhat.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Nysal Jan K.A" <nysal@linux.ibm.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Russel King <linux@armlinux.org.uk>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Cc: Thomas Huth <thuth@redhat.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-09-21 14:22:15 -07:00
Matthew Wilcox (Oracle)andAndrew Morton 53fbef56e0 mm: introduce memdesc_flags_t 
Patch series "Add and use memdesc_flags_t".

At some point struct page will be separated from struct slab and struct
folio.  This is a step towards that by introducing a type for the 'flags'
word of all three structures.  This gives us a certain amount of type
safety by establishing that some of these unsigned longs are different
from other unsigned longs in that they contain things like node ID,
section number and zone number in the upper bits.  That lets us have
functions that can be easily called by anyone who has a slab, folio or
page (but not easily by anyone else) to get the node or zone.

There's going to be some unusual merge problems with this as some odd bits
of the kernel decide they want to print out the flags value or something
similar by writing page->flags and now they'll need to write page->flags.f
instead.  That's most of the churn here.  Maybe we should be removing
these things from the debug output?


This patch (of 11):

Wrap the unsigned long flags in a typedef.  In upcoming patches, this will
provide a strong hint that you can't just pass a random unsigned long to
functions which take this as an argument.

[willy@infradead.org: s/flags/flags.f/ in several architectures]
  Link: https://lkml.kernel.org/r/aKMgPRLD-WnkPxYm@casper.infradead.org
[nicola.vetrini@gmail.com: mips: fix compilation error]
  Link: https://lore.kernel.org/lkml/CA+G9fYvkpmqGr6wjBNHY=dRp71PLCoi2341JxOudi60yqaeUdg@mail.gmail.com/
  Link: https://lkml.kernel.org/r/20250825214245.1838158-1-nicola.vetrini@gmail.com
Link: https://lkml.kernel.org/r/20250805172307.1302730-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20250805172307.1302730-2-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Zi Yan <ziy@nvidia.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-09-13 16:55:07 -07:00
David HildenbrandandAndrew Morton f8e97613fe mm: convert VM_PFNMAP tracking to pfnmap_track() + pfnmap_untrack() 
Let's use our new interface.  In remap_pfn_range(), we'll now decide
whether we have to track (full VMA covered) or only lookup the cachemode
(partial VMA covered).

Remember what we have to untrack by linking it from the VMA.  When
duplicating VMAs (e.g., splitting, mremap, fork), we'll handle it similar
to anon VMA names, and use a kref to share the tracking.

Once the last VMA un-refs our tracking data, we'll do the untracking,
which simplifies things a lot and should sort our various issues we saw
recently, for example, when partially unmapping/zapping a tracked VMA.

This change implies that we'll keep tracking the original PFN range even
after splitting + partially unmapping it: not too bad, because it was not
working reliably before.  The only thing that kind-of worked before was
shrinking such a mapping using mremap(): we managed to adjust the
reservation in a hacky way, now we won't adjust the reservation but leave
it around until all involved VMAs are gone.

If that ever turns out to be an issue, we could hook into VM splitting
code and split the tracking; however, that adds complexity that might not
be required, so we'll keep it simple for now.

Link: https://lkml.kernel.org/r/20250512123424.637989-5-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Ingo Molnar <mingo@kernel.org>	[x86 bits]
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Dave Airlie <airlied@gmail.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Cc: Tvrtko Ursulin <tursulin@ursulin.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-05-22 14:55:37 -07:00
Yu ZhaoandAndrew Morton 4d5d14a01e mm/mglru: rework workingset protection 
With the aging feedback no longer considering the distribution of folios
in each generation, rework workingset protection to better distribute
folios across MAX_NR_GENS.  This is achieved by reusing PG_workingset and
PG_referenced/LRU_REFS_FLAGS in a slightly different way.

For folios accessed multiple times through file descriptors, make
lru_gen_inc_refs() set additional bits of LRU_REFS_WIDTH in folio->flags
after PG_referenced, then PG_workingset after LRU_REFS_WIDTH.  After all
its bits are set, i.e., LRU_REFS_FLAGS|BIT(PG_workingset), a folio is
lazily promoted into the second oldest generation in the eviction path. 
And when folio_inc_gen() does that, it clears LRU_REFS_FLAGS so that
lru_gen_inc_refs() can start over.  For this case, LRU_REFS_MASK is only
valid when PG_referenced is set.

For folios accessed multiple times through page tables, folio_update_gen()
from a page table walk or lru_gen_set_refs() from a rmap walk sets
PG_referenced after the accessed bit is cleared for the first time. 
Thereafter, those two paths set PG_workingset and promote folios to the
youngest generation.  Like folio_inc_gen(), when folio_update_gen() does
that, it also clears PG_referenced.  For this case, LRU_REFS_MASK is not
used.

For both of the cases, after PG_workingset is set on a folio, it remains
until this folio is either reclaimed, or "deactivated" by
lru_gen_clear_refs().  It can be set again if lru_gen_test_recent()
returns true upon a refault.

When adding folios to the LRU lists, lru_gen_folio_seq() distributes
them as follows:
+---------------------------------+---------------------------------+
|    Accessed thru page tables    | Accessed thru file descriptors  |
+---------------------------------+---------------------------------+
| PG_active (set while isolated)  |                                 |
+----------------+----------------+----------------+----------------+
| PG_workingset  | PG_referenced  | PG_workingset  | LRU_REFS_FLAGS |
+---------------------------------+---------------------------------+
|<--------- MIN_NR_GENS --------->|                                 |
|<-------------------------- MAX_NR_GENS -------------------------->|

After this patch, some typical client and server workloads showed
improvements under heavy memory pressure.  For example, Python TPC-C,
which was used to benchmark a different approach [1] to better detect
refault distances, showed a significant decrease in total refaults:

                            Before      After      Change
  Time (seconds)            10801       10801      0%
  Executed (transactions)   41472       43663      +5%
  workingset_nodes          109070      120244     +10%
  workingset_refault_anon   5019627     7281831    +45%
  workingset_refault_file   1294678786  554855564  -57%
  workingset_refault_total  1299698413  562137395  -57%

[1] https://lore.kernel.org/20230920190244.16839-1-ryncsn@gmail.com/

Link: https://lkml.kernel.org/r/20241231043538.4075764-7-yuzhao@google.com
Signed-off-by: Yu Zhao <yuzhao@google.com>
Reported-by: Kairui Song <kasong@tencent.com>
Closes: https://lore.kernel.org/CAOUHufahuWcKf5f1Sg3emnqX+cODuR=2TQo7T4Gr-QYLujn4RA@mail.gmail.com/
Tested-by: Kalesh Singh <kaleshsingh@google.com>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Bharata B Rao <bharata@amd.com>
Cc: David Stevens <stevensd@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-01-25 20:22:39 -08:00
Qi ZhengandAndrew Morton 735fad44b5 mm: zap_install_uffd_wp_if_needed: return whether uffd-wp pte has been re-installed 
In some cases, we'll replace the none pte with an uffd-wp swap special pte
marker when necessary.  Let's expose this information to the caller
through the return value, so that subsequent commits can use this
information to detect whether the PTE page is empty.

Link: https://lkml.kernel.org/r/9d4516554724eda87d6576468042a1741c475413.1733305182.git.zhengqi.arch@bytedance.com
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Cc: Zach O'Keefe <zokeefe@google.com>
Cc: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-01-13 22:40:47 -08:00
Lorenzo StoakesandAndrew Morton 7c53dfbdb0 mm: add PTE_MARKER_GUARD PTE marker 
Add a new PTE marker that results in any access causing the accessing
process to segfault.

This is preferable to PTE_MARKER_POISONED, which results in the same
handling as hardware poisoned memory, and is thus undesirable for cases
where we simply wish to 'soft' poison a range.

This is in preparation for implementing the ability to specify guard pages
at the page table level, i.e.  ranges that, when accessed, should cause
process termination.

Additionally, rename zap_drop_file_uffd_wp() to zap_drop_markers() - the
function checks the ZAP_FLAG_DROP_MARKER flag so naming it for this single
purpose was simply incorrect.

We then reuse the same logic to determine whether a zap should clear a
guard entry - this should only be performed on teardown and never on
MADV_DONTNEED or MADV_FREE.

We additionally add a WARN_ON_ONCE() in hugetlb logic should a guard
marker be encountered there, as we explicitly do not support this
operation and this should not occur.

Link: https://lkml.kernel.org/r/f47f3d5acca2dcf9bbf655b6d33f3dc713e4a4a0.1730123433.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: Vlastimil Babka <vbabkba@suse.cz>
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Suggested-by: Jann Horn <jannh@google.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Cc: Arnd Bergmann <arnd@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Chris Zankel <chris@zankel.net>
Cc: Helge Deller <deller@gmx.de>
Cc: James E.J. Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Jeff Xu <jeffxu@chromium.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2024-11-11 00:26:44 -08:00
Wei XuandAndrew Morton f1001f3d3b mm/mglru: reset page lru tier bits when activating 
When a folio is activated, lru_gen_add_folio() moves the folio to the
youngest generation.  But unlike folio_update_gen()/folio_inc_gen(),
lru_gen_add_folio() doesn't reset the folio lru tier bits (LRU_REFS_MASK |
LRU_REFS_FLAGS).  This inconsistency can affect how pages are aged via
folio_mark_accessed() (e.g.  fd accesses), though no user visible impact
related to this has been detected yet.

Note that lru_gen_add_folio() cannot clear PG_workingset if the activation
is due to workingset refault, otherwise PSI accounting will be skipped. 
So fix lru_gen_add_folio() to clear the lru tier bits other than
PG_workingset when activating a folio, and also clear all the lru tier
bits when a folio is activated via folio_activate() in
lru_gen_look_around().

Link: https://lkml.kernel.org/r/20241017181528.3358821-1-weixugc@google.com
Fixes: 018ee47f14 ("mm: multi-gen LRU: exploit locality in rmap")
Signed-off-by: Wei Xu <weixugc@google.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Jan Alexander Steffens <heftig@archlinux.org>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2024-11-06 20:11:15 -08:00
Zhaoyang HuangandAndrew Morton 473c371254 mm: migrate LRU_REFS_MASK bits in folio_migrate_flags 
Bits of LRU_REFS_MASK are not inherited during migration which lead to new
folio start from tier0 when MGLRU enabled.  Try to bring as much bits of
folio->flags as possible since compaction and alloc_contig_range which
introduce migration do happen at times.

Link: https://lkml.kernel.org/r/20240926050647.5653-1-zhaoyang.huang@unisoc.com
Signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
Suggested-by: Yu Zhao <yuzhao@google.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2024-11-05 16:56:29 -08:00
Yu ZhaoandAndrew Morton 081488051d mm/mglru: fix underprotected page cache 
Unmapped folios accessed through file descriptors can be underprotected. 
Those folios are added to the oldest generation based on:

1. The fact that they are less costly to reclaim (no need to walk the
   rmap and flush the TLB) and have less impact on performance (don't
   cause major PFs and can be non-blocking if needed again).
2. The observation that they are likely to be single-use. E.g., for
   client use cases like Android, its apps parse configuration files
   and store the data in heap (anon); for server use cases like MySQL,
   it reads from InnoDB files and holds the cached data for tables in
   buffer pools (anon).

However, the oldest generation can be very short lived, and if so, it
doesn't provide the PID controller with enough time to respond to a surge
of refaults.  (Note that the PID controller uses weighted refaults and
those from evicted generations only take a half of the whole weight.) In
other words, for a short lived generation, the moving average smooths out
the spike quickly.

To fix the problem:
1. For folios that are already on LRU, if they can be beyond the
   tracking range of tiers, i.e., five accesses through file
   descriptors, move them to the second oldest generation to give them
   more time to age. (Note that tiers are used by the PID controller
   to statistically determine whether folios accessed multiple times
   through file descriptors are worth protecting.)
2. When adding unmapped folios to LRU, adjust the placement of them so
   that they are not too close to the tail. The effect of this is
   similar to the above.

On Android, launching 55 apps sequentially:
                           Before     After      Change
  workingset_refault_anon  25641024   25598972   0%
  workingset_refault_file  115016834  106178438  -8%

Link: https://lkml.kernel.org/r/20231208061407.2125867-1-yuzhao@google.com
Fixes: ac35a49023 ("mm: multi-gen LRU: minimal implementation")
Signed-off-by: Yu Zhao <yuzhao@google.com>
Reported-by: Charan Teja Kalla <quic_charante@quicinc.com>
Tested-by: Kalesh Singh <kaleshsingh@google.com>
Cc: T.J. Mercier <tjmercier@google.com>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Jaroslav Pulchart <jaroslav.pulchart@gooddata.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2023-12-12 17:20:19 -08:00
Lorenzo StoakesandAndrew Morton 3657fdc245 mm: move vma_policy() and anon_vma_name() decls to mm_types.h 
Patch series "Abstract vma_merge() and split_vma()", v4.

The vma_merge() interface is very confusing and its implementation has led
to numerous bugs as a result of that confusion.

In addition there is duplication both in invocation of vma_merge(), but
also in the common mprotect()-style pattern of attempting a merge, then if
this fails, splitting the portion of a VMA about to have its attributes
changed.

This pattern has been copy/pasted around the kernel in each instance where
such an operation has been required, each very slightly modified from the
last to make it even harder to decipher what is going on.

Simplify the whole thing by dividing the actual uses of vma_merge() and
split_vma() into specific and abstracted functions and de-duplicate the
vma_merge()/split_vma() pattern altogether.

Doing so also opens the door to changing how vma_merge() is implemented -
by knowing precisely what cases a caller is invoking rather than having a
central interface where anything might happen we can untangle the brittle
and confusing vma_merge() implementation into something more workable.

For mprotect()-like cases we introduce vma_modify() which performs the
vma_merge()/split_vma() pattern, returning a pointer to either the merged
or split VMA or an ERR_PTR(err) if the splits fail.

We provide a number of inline helper functions to make things even clearer:-

* vma_modify_flags()      - Prepare to modify the VMA's flags.
* vma_modify_flags_name() - Prepare to modify the VMA's flags/anon_vma_name
* vma_modify_policy()     - Prepare to modify the VMA's mempolicy.
* vma_modify_flags_uffd() - Prepare to modify the VMA's flags/uffd context.

For cases where a new VMA is attempted to be merged with adjacent VMAs we
add:-

* vma_merge_new_vma() - Prepare to merge a new VMA.
* vma_merge_extend()  - Prepare to extend the end of a new VMA.


This patch (of 5):

The vma_policy() define is a helper specifically for a VMA field so it
makes sense to host it in the memory management types header.

The anon_vma_name(), anon_vma_name_alloc() and anon_vma_name_free()
functions are a little out of place in mm_inline.h as they define external
functions, and so it makes sense to locate them in mm_types.h.

The purpose of these relocations is to make it possible to abstract static
inline wrappers which invoke both of these helpers.

Link: https://lkml.kernel.org/r/cover.1697043508.git.lstoakes@gmail.com
Link: https://lkml.kernel.org/r/24bfc6c9e382fffbcb0ea8d424392c27d56cc8ca.1697043508.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2023-10-18 14:34:18 -07:00
Andrew Morton f92cedfa39 mm-make-pte_marker_swapin_error-more-general-fix 
fix CONFIG_MMU=n build

Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2023-08-18 10:12:16 -07:00
Axel RasmussenandAndrew Morton af19487f00 mm: make PTE_MARKER_SWAPIN_ERROR more general 
Patch series "add UFFDIO_POISON to simulate memory poisoning with UFFD",
v4.

This series adds a new userfaultfd feature, UFFDIO_POISON. See commit 4
for a detailed description of the feature.


This patch (of 8):

Future patches will reuse PTE_MARKER_SWAPIN_ERROR to implement
UFFDIO_POISON, so make some various preparations for that:

First, rename it to just PTE_MARKER_POISONED.  The "SWAPIN" can be
confusing since we're going to re-use it for something not really related
to swap.  This can be particularly confusing for things like hugetlbfs,
which doesn't support swap whatsoever.  Also rename some various helper
functions.

Next, fix pte marker copying for hugetlbfs.  Previously, it would WARN on
seeing a PTE_MARKER_SWAPIN_ERROR, since hugetlbfs doesn't support swap. 
But, since we're going to re-use it, we want it to go ahead and copy it
just like non-hugetlbfs memory does today.  Since the code to do this is
more complicated now, pull it out into a helper which can be re-used in
both places.  While we're at it, also make it slightly more explicit in
its handling of e.g.  uffd wp markers.

For non-hugetlbfs page faults, instead of returning VM_FAULT_SIGBUS for an
error entry, return VM_FAULT_HWPOISON.  For most cases this change doesn't
matter, e.g.  a userspace program would receive a SIGBUS either way.  But
for UFFDIO_POISON, this change will let KVM guests get an MCE out of the
box, instead of giving a SIGBUS to the hypervisor and requiring it to
somehow inject an MCE.

Finally, for hugetlbfs faults, handle PTE_MARKER_POISONED, and return
VM_FAULT_HWPOISON_LARGE in such cases.  Note that this can't happen today
because the lack of swap support means we'll never end up with such a PTE
anyway, but this behavior will be needed once such entries *can* show up
via UFFDIO_POISON.

Link: https://lkml.kernel.org/r/20230707215540.2324998-1-axelrasmussen@google.com
Link: https://lkml.kernel.org/r/20230707215540.2324998-2-axelrasmussen@google.com
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Acked-by: Peter Xu <peterx@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Gaosheng Cui <cuigaosheng1@huawei.com>
Cc: Huang, Ying <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Jan Alexander Steffens (heftig) <heftig@archlinux.org>
Cc: Jiaqi Yan <jiaqiyan@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nadav Amit <namit@vmware.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: T.J. Alumbaugh <talumbau@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: ZhangPeng <zhangpeng362@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2023-08-18 10:12:16 -07:00
Kefeng WangandAndrew Morton 7302338a14 mm: kill [add|del]_page_to_lru_list() 
Now no one call [add|del]_page_to_lru_list(), let's drop unused page
interfaces.

Link:https://lkml.kernel.org/r/20230619110718.65679-2-wangkefeng.wang@huawei.com
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Acked-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: James Gowans <jgowans@amazon.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2023-06-23 16:59:31 -07:00
Ryan RobertsandAndrew Morton c33c794828 mm: ptep_get() conversion 
Convert all instances of direct pte_t* dereferencing to instead use
ptep_get() helper.  This means that by default, the accesses change from a
C dereference to a READ_ONCE().  This is technically the correct thing to
do since where pgtables are modified by HW (for access/dirty) they are
volatile and therefore we should always ensure READ_ONCE() semantics.

But more importantly, by always using the helper, it can be overridden by
the architecture to fully encapsulate the contents of the pte.  Arch code
is deliberately not converted, as the arch code knows best.  It is
intended that arch code (arm64) will override the default with its own
implementation that can (e.g.) hide certain bits from the core code, or
determine young/dirty status by mixing in state from another source.

Conversion was done using Coccinelle:

----

// $ make coccicheck \
//          COCCI=ptepget.cocci \
//          SPFLAGS="--include-headers" \
//          MODE=patch

virtual patch

@ depends on patch @
pte_t *v;
@@

- *v
+ ptep_get(v)

----

Then reviewed and hand-edited to avoid multiple unnecessary calls to
ptep_get(), instead opting to store the result of a single call in a
variable, where it is correct to do so.  This aims to negate any cost of
READ_ONCE() and will benefit arch-overrides that may be more complex.

Included is a fix for an issue in an earlier version of this patch that
was pointed out by kernel test robot.  The issue arose because config
MMU=n elides definition of the ptep helper functions, including
ptep_get().  HUGETLB_PAGE=n configs still define a simple
huge_ptep_clear_flush() for linking purposes, which dereferences the ptep.
So when both configs are disabled, this caused a build error because
ptep_get() is not defined.  Fix by continuing to do a direct dereference
when MMU=n.  This is safe because for this config the arch code cannot be
trying to virtualize the ptes because none of the ptep helpers are
defined.

Link: https://lkml.kernel.org/r/20230612151545.3317766-4-ryan.roberts@arm.com
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202305120142.yXsNEo6H-lkp@intel.com/
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Dimitri Sivanich <dimitri.sivanich@hpe.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: SeongJae Park <sj@kernel.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2023-06-19 16:19:25 -07:00
Peter XuandAndrew Morton 2bad466cc9 mm/uffd: UFFD_FEATURE_WP_UNPOPULATED 
Patch series "mm/uffd: Add feature bit UFFD_FEATURE_WP_UNPOPULATED", v4.

The new feature bit makes anonymous memory acts the same as file memory on
userfaultfd-wp in that it'll also wr-protect none ptes.

It can be useful in two cases:

(1) Uffd-wp app that needs to wr-protect none ptes like QEMU snapshot,
    so pre-fault can be replaced by enabling this flag and speed up
    protections

(2) It helps to implement async uffd-wp mode that Muhammad is working on [1]

It's debatable whether this is the most ideal solution because with the
new feature bit set, wr-protect none pte needs to pre-populate the
pgtables to the last level (PAGE_SIZE).  But it seems fine so far to
service either purpose above, so we can leave optimizations for later.

The series brings pte markers to anonymous memory too.  There's some
change in the common mm code path in the 1st patch, great to have some eye
looking at it, but hopefully they're still relatively straightforward.


This patch (of 2):

This is a new feature that controls how uffd-wp handles none ptes.  When
it's set, the kernel will handle anonymous memory the same way as file
memory, by allowing the user to wr-protect unpopulated ptes.

File memories handles none ptes consistently by allowing wr-protecting of
none ptes because of the unawareness of page cache being exist or not. 
For anonymous it was not as persistent because we used to assume that we
don't need protections on none ptes or known zero pages.

One use case of such a feature bit was VM live snapshot, where if without
wr-protecting empty ptes the snapshot can contain random rubbish in the
holes of the anonymous memory, which can cause misbehave of the guest when
the guest OS assumes the pages should be all zeros.

QEMU worked it around by pre-populate the section with reads to fill in
zero page entries before starting the whole snapshot process [1].

Recently there's another need raised on using userfaultfd wr-protect for
detecting dirty pages (to replace soft-dirty in some cases) [2].  In that
case if without being able to wr-protect none ptes by default, the dirty
info can get lost, since we cannot treat every none pte to be dirty (the
current design is identify a page dirty based on uffd-wp bit being
cleared).

In general, we want to be able to wr-protect empty ptes too even for
anonymous.

This patch implements UFFD_FEATURE_WP_UNPOPULATED so that it'll make
uffd-wp handling on none ptes being consistent no matter what the memory
type is underneath.  It doesn't have any impact on file memories so far
because we already have pte markers taking care of that.  So it only
affects anonymous.

The feature bit is by default off, so the old behavior will be maintained.
Sometimes it may be wanted because the wr-protect of none ptes will
contain overheads not only during UFFDIO_WRITEPROTECT (by applying pte
markers to anonymous), but also on creating the pgtables to store the pte
markers.  So there's potentially less chance of using thp on the first
fault for a none pmd or larger than a pmd.

The major implementation part is teaching the whole kernel to understand
pte markers even for anonymously mapped ranges, meanwhile allowing the
UFFDIO_WRITEPROTECT ioctl to apply pte markers for anonymous too when the
new feature bit is set.

Note that even if the patch subject starts with mm/uffd, there're a few
small refactors to major mm path of handling anonymous page faults.  But
they should be straightforward.

With WP_UNPOPUATED, application like QEMU can avoid pre-read faults all
the memory before wr-protect during taking a live snapshot.  Quotting from
Muhammad's test result here [3] based on a simple program [4]:

  (1) With huge page disabled
  echo madvise > /sys/kernel/mm/transparent_hugepage/enabled
  ./uffd_wp_perf
  Test DEFAULT: 4
  Test PRE-READ: 1111453 (pre-fault 1101011)
  Test MADVISE: 278276 (pre-fault 266378)
  Test WP-UNPOPULATE: 11712

  (2) With Huge page enabled
  echo always > /sys/kernel/mm/transparent_hugepage/enabled
  ./uffd_wp_perf
  Test DEFAULT: 4
  Test PRE-READ: 22521 (pre-fault 22348)
  Test MADVISE: 4909 (pre-fault 4743)
  Test WP-UNPOPULATE: 14448

There'll be a great perf boost for no-thp case, while for thp enabled with
extreme case of all-thp-zero WP_UNPOPULATED can be slower than MADVISE,
but that's low possibility in reality, also the overhead was not reduced
but postponed until a follow up write on any huge zero thp, so potentially
it is faster by making the follow up writes slower.

[1] https://lore.kernel.org/all/20210401092226.102804-4-andrey.gruzdev@virtuozzo.com/
[2] https://lore.kernel.org/all/Y+v2HJ8+3i%2FKzDBu@x1n/
[3] https://lore.kernel.org/all/d0eb0a13-16dc-1ac1-653a-78b7273781e3@collabora.com/
[4] https://github.com/xzpeter/clibs/blob/master/uffd-test/uffd-wp-perf.c

[peterx@redhat.com: comment changes, oneliner fix to khugepaged]
  Link: https://lkml.kernel.org/r/ZB2/8jPhD3fpx5U8@x1n
Link: https://lkml.kernel.org/r/20230309223711.823547-1-peterx@redhat.com
Link: https://lkml.kernel.org/r/20230309223711.823547-2-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Paul Gofman <pgofman@codeweavers.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2023-04-05 19:42:44 -07:00
T.J. AlumbaughandAndrew Morton 36c7b4db7c mm: multi-gen LRU: section for memcg LRU 
Move memcg LRU code into a dedicated section.  Improve the design doc to
outline its architecture.

Link: https://lkml.kernel.org/r/20230118001827.1040870-5-talumbau@google.com
Signed-off-by: T.J. Alumbaugh <talumbau@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2023-02-02 22:33:27 -08:00
Yu ZhaoandAndrew Morton 17e810229c mm: support POSIX_FADV_NOREUSE 
This patch adds POSIX_FADV_NOREUSE to vma_has_recency() so that the LRU
algorithm can ignore access to mapped files marked by this flag.

The advantages of POSIX_FADV_NOREUSE are:
1. Unlike MADV_SEQUENTIAL and MADV_RANDOM, it does not alter the
   default readahead behavior.
2. Unlike MADV_SEQUENTIAL and MADV_RANDOM, it does not split VMAs and
   therefore does not take mmap_lock.
3. Unlike MADV_COLD, setting it has a negligible cost, regardless of
   how many pages it affects.

Its limitations are:
1. Like POSIX_FADV_RANDOM and POSIX_FADV_SEQUENTIAL, it currently does
   not support range. IOW, its scope is the entire file.
2. It currently does not ignore access through file descriptors.
   Specifically, for the active/inactive LRU, given a file page shared
   by two users and one of them having set POSIX_FADV_NOREUSE on the
   file, this page will be activated upon the second user accessing
   it. This corner case can be covered by checking POSIX_FADV_NOREUSE
   before calling folio_mark_accessed() on the read path. But it is
   considered not worth the effort.

There have been a few attempts to support POSIX_FADV_NOREUSE, e.g., [1]. 
This time the goal is to fill a niche: a few desktop applications, e.g.,
large file transferring and video encoding/decoding, want fast file
streaming with mmap() rather than direct IO.  Among those applications, an
SVT-AV1 regression was reported when running with MGLRU [2].  The
following test can reproduce that regression.

  kb=$(awk '/MemTotal/ { print $2 }' /proc/meminfo)
  kb=$((kb - 8*1024*1024))

  modprobe brd rd_nr=1 rd_size=$kb
  dd if=/dev/zero of=/dev/ram0 bs=1M

  mkfs.ext4 /dev/ram0
  mount /dev/ram0 /mnt/
  swapoff -a

  fallocate -l 8G /mnt/swapfile
  mkswap /mnt/swapfile
  swapon /mnt/swapfile

  wget http://ultravideo.cs.tut.fi/video/Bosphorus_3840x2160_120fps_420_8bit_YUV_Y4M.7z
  7z e -o/mnt/ Bosphorus_3840x2160_120fps_420_8bit_YUV_Y4M.7z
  SvtAv1EncApp --preset 12 -w 3840 -h 2160 \
               -i /mnt/Bosphorus_3840x2160.y4m

For MGLRU, the following change showed a [9-11]% increase in FPS,
which makes it on par with the active/inactive LRU.

  patch Source/App/EncApp/EbAppMain.c <<EOF
  31a32
  > #include <fcntl.h>
  35d35
  < #include <fcntl.h> /* _O_BINARY */
  117a118
  >             posix_fadvise(config->mmap.fd, 0, 0, POSIX_FADV_NOREUSE);
  EOF

[1] https://lore.kernel.org/r/1308923350-7932-1-git-send-email-andrea@betterlinux.com/
[2] https://openbenchmarking.org/result/2209259-PTS-MGLRU8GB57

Link: https://lkml.kernel.org/r/20221230215252.2628425-2-yuzhao@google.com
Signed-off-by: Yu Zhao <yuzhao@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andrea Righi <andrea.righi@canonical.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michael Larabel <Michael@MichaelLarabel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2023-01-18 17:12:57 -08:00
Yu ZhaoandAndrew Morton 8788f67814 mm: add vma_has_recency() 
Add vma_has_recency() to indicate whether a VMA may exhibit temporal
locality that the LRU algorithm relies on.

This function returns false for VMAs marked by VM_SEQ_READ or
VM_RAND_READ.  While the former flag indicates linear access, i.e., a
special case of spatial locality, both flags indicate a lack of temporal
locality, i.e., the reuse of an area within a relatively small duration.

"Recency" is chosen over "locality" to avoid confusion between temporal
and spatial localities.

Before this patch, the active/inactive LRU only ignored the accessed bit
from VMAs marked by VM_SEQ_READ.  After this patch, the active/inactive
LRU and MGLRU share the same logic: they both ignore the accessed bit if
vma_has_recency() returns false.

For the active/inactive LRU, the following fio test showed a [6, 8]%
increase in IOPS when randomly accessing mapped files under memory
pressure.

  kb=$(awk '/MemTotal/ { print $2 }' /proc/meminfo)
  kb=$((kb - 8*1024*1024))

  modprobe brd rd_nr=1 rd_size=$kb
  dd if=/dev/zero of=/dev/ram0 bs=1M

  mkfs.ext4 /dev/ram0
  mount /dev/ram0 /mnt/
  swapoff -a

  fio --name=test --directory=/mnt/ --ioengine=mmap --numjobs=8 \
      --size=8G --rw=randrw --time_based --runtime=10m \
      --group_reporting

The discussion that led to this patch is here [1].  Additional test
results are available in that thread.

[1] https://lore.kernel.org/r/Y31s%2FK8T85jh05wH@google.com/

Link: https://lkml.kernel.org/r/20221230215252.2628425-1-yuzhao@google.com
Signed-off-by: Yu Zhao <yuzhao@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andrea Righi <andrea.righi@canonical.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michael Larabel <Michael@MichaelLarabel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2023-01-18 17:12:57 -08:00