Evictable pages are divided into multiple generations for each lruvec.
The youngest generation number is stored in lrugen->max_seq for both
anon and file types as they are aged on an equal footing. The oldest
generation numbers are stored in lrugen->min_seq[] separately for anon
and file types as clean file pages can be evicted regardless of swap
constraints. These three variables are monotonically increasing.
Generation numbers are truncated into order_base_2(MAX_NR_GENS+1) bits
in order to fit into the gen counter in folio->flags. Each truncated
generation number is an index to lrugen->lists[]. The sliding window
technique is used to track at least MIN_NR_GENS and at most
MAX_NR_GENS generations. The gen counter stores a value within [1,
MAX_NR_GENS] while a page is on one of lrugen->lists[]. Otherwise it
stores 0.
There are two conceptually independent procedures: "the aging", which
produces young generations, and "the eviction", which consumes old
generations. They form a closed-loop system, i.e., "the page reclaim".
Both procedures can be invoked from userspace for the purposes of working
set estimation and proactive reclaim. These techniques are commonly used
to optimize job scheduling (bin packing) in data centers [1][2].
To avoid confusion, the terms "hot" and "cold" will be applied to the
multi-gen LRU, as a new convention; the terms "active" and "inactive" will
be applied to the active/inactive LRU, as usual.
The protection of hot pages and the selection of cold pages are based
on page access channels and patterns. There are two access channels:
one through page tables and the other through file descriptors. The
protection of the former channel is by design stronger because:
1. The uncertainty in determining the access patterns of the former
channel is higher due to the approximation of the accessed bit.
2. The cost of evicting the former channel is higher due to the TLB
flushes required and the likelihood of encountering the dirty bit.
3. The penalty of underprotecting the former channel is higher because
applications usually do not prepare themselves for major page
faults like they do for blocked I/O. E.g., GUI applications
commonly use dedicated I/O threads to avoid blocking rendering
threads.
There are also two access patterns: one with temporal locality and the
other without. For the reasons listed above, the former channel is
assumed to follow the former pattern unless VM_SEQ_READ or VM_RAND_READ is
present; the latter channel is assumed to follow the latter pattern unless
outlying refaults have been observed [3][4].
The next patch will address the "outlying refaults". Three macros, i.e.,
LRU_REFS_WIDTH, LRU_REFS_PGOFF and LRU_REFS_MASK, used later are added in
this patch to make the entire patchset less diffy.
A page is added to the youngest generation on faulting. The aging needs
to check the accessed bit at least twice before handing this page over to
the eviction. The first check takes care of the accessed bit set on the
initial fault; the second check makes sure this page has not been used
since then. This protocol, AKA second chance, requires a minimum of two
generations, hence MIN_NR_GENS.
[1] https://dl.acm.org/doi/10.1145/3297858.3304053
[2] https://dl.acm.org/doi/10.1145/3503222.3507731
[3] https://lwn.net/Articles/495543/
[4] https://lwn.net/Articles/815342/
Link: https://lkml.kernel.org/r/20220918080010.2920238-6-yuzhao@google.com
Signed-off-by: Yu Zhao <yuzhao@google.com>
Acked-by: Brian Geffon <bgeffon@google.com>
Acked-by: Jan Alexander Steffens (heftig) <heftig@archlinux.org>
Acked-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Acked-by: Steven Barrett <steven@liquorix.net>
Acked-by: Suleiman Souhlal <suleiman@google.com>
Tested-by: Daniel Byrne <djbyrne@mtu.edu>
Tested-by: Donald Carr <d@chaos-reins.com>
Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
Tested-by: Shuang Zhai <szhai2@cs.rochester.edu>
Tested-by: Sofia Trinh <sofia.trinh@edi.works>
Tested-by: Vaibhav Jain <vaibhav@linux.ibm.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michael Larabel <Michael@MichaelLarabel.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "Simplify hugetlb vmemmap and improve its readability", v2.
This series aims to simplify hugetlb vmemmap and improve its readability.
This patch (of 8):
The name hugetlb_optimize_vmemmap_enabled() a bit confusing as it tests
two conditions (enabled and pages in use). Instead of coming up to an
appropriate name, we could just delete it. There is already a discussion
about deleting it in thread [1].
There is only one user of hugetlb_optimize_vmemmap_enabled() outside of
hugetlb_vmemmap, that is flush_dcache_page() in arch/arm64/mm/flush.c.
However, it does not need to call hugetlb_optimize_vmemmap_enabled() in
flush_dcache_page() since HugeTLB pages are always fully mapped and only
head page will be set PG_dcache_clean meaning only head page's flag may
need to be cleared (see commit cf5a501d98). So it is easy to remove
hugetlb_optimize_vmemmap_enabled().
Link: https://lore.kernel.org/all/c77c61c8-8a5a-87e8-db89-d04d8aaab4cc@oracle.com/ [1]
Link: https://lkml.kernel.org/r/20220628092235.91270-2-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Pull MM updates from Andrew Morton:
"Most of the MM queue. A few things are still pending.
Liam's maple tree rework didn't make it. This has resulted in a few
other minor patch series being held over for next time.
Multi-gen LRU still isn't merged as we were waiting for mapletree to
stabilize. The current plan is to merge MGLRU into -mm soon and to
later reintroduce mapletree, with a view to hopefully getting both
into 6.1-rc1.
Summary:
- The usual batches of cleanups from Baoquan He, Muchun Song, Miaohe
Lin, Yang Shi, Anshuman Khandual and Mike Rapoport
- Some kmemleak fixes from Patrick Wang and Waiman Long
- DAMON updates from SeongJae Park
- memcg debug/visibility work from Roman Gushchin
- vmalloc speedup from Uladzislau Rezki
- more folio conversion work from Matthew Wilcox
- enhancements for coherent device memory mapping from Alex Sierra
- addition of shared pages tracking and CoW support for fsdax, from
Shiyang Ruan
- hugetlb optimizations from Mike Kravetz
- Mel Gorman has contributed some pagealloc changes to improve
latency and realtime behaviour.
- mprotect soft-dirty checking has been improved by Peter Xu
- Many other singleton patches all over the place"
[ XFS merge from hell as per Darrick Wong in
https://lore.kernel.org/all/YshKnxb4VwXycPO8@magnolia/ ]
* tag 'mm-stable-2022-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (282 commits)
tools/testing/selftests/vm/hmm-tests.c: fix build
mm: Kconfig: fix typo
mm: memory-failure: convert to pr_fmt()
mm: use is_zone_movable_page() helper
hugetlbfs: fix inaccurate comment in hugetlbfs_statfs()
hugetlbfs: cleanup some comments in inode.c
hugetlbfs: remove unneeded header file
hugetlbfs: remove unneeded hugetlbfs_ops forward declaration
hugetlbfs: use helper macro SZ_1{K,M}
mm: cleanup is_highmem()
mm/hmm: add a test for cross device private faults
selftests: add soft-dirty into run_vmtests.sh
selftests: soft-dirty: add test for mprotect
mm/mprotect: fix soft-dirty check in can_change_pte_writable()
mm: memcontrol: fix potential oom_lock recursion deadlock
mm/gup.c: fix formatting in check_and_migrate_movable_page()
xfs: fail dax mount if reflink is enabled on a partition
mm/memcontrol.c: remove the redundant updating of stats_flush_threshold
userfaultfd: don't fail on unrecognized features
hugetlb_cgroup: fix wrong hugetlb cgroup numa stat
...
These drivers are rather uncomfortably hammered into the
address_space_operations hole. They aren't filesystems and don't behave
like filesystems. They just need their own movable_operations structure,
which we can point to directly from page->mapping.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
For now, the feature of hugetlb_free_vmemmap is not compatible with the
feature of memory_hotplug.memmap_on_memory, and hugetlb_free_vmemmap takes
precedence over memory_hotplug.memmap_on_memory. However, someone wants
to make memory_hotplug.memmap_on_memory takes precedence over
hugetlb_free_vmemmap since memmap_on_memory makes it more likely to
succeed memory hotplug in close-to-OOM situations. So the decision of
making hugetlb_free_vmemmap take precedence is not wise and elegant.
The proper approach is to have hugetlb_vmemmap.c do the check whether the
section which the HugeTLB pages belong to can be optimized. If the
section's vmemmap pages are allocated from the added memory block itself,
hugetlb_free_vmemmap should refuse to optimize the vmemmap, otherwise, do
the optimization. Then both kernel parameters are compatible. So this
patch introduces VmemmapSelfHosted to mask any non-optimizable vmemmap
pages. The hugetlb_vmemmap can use this flag to detect if a vmemmap page
can be optimized.
[songmuchun@bytedance.com: walk vmemmap page tables to avoid false-positive]
Link: https://lkml.kernel.org/r/20220620110616.12056-3-songmuchun@bytedance.com
Link: https://lkml.kernel.org/r/20220617135650.74901-3-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Co-developed-by: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Pull MM updates from Andrew Morton:
"Almost all of MM here. A few things are still getting finished off,
reviewed, etc.
- Yang Shi has improved the behaviour of khugepaged collapsing of
readonly file-backed transparent hugepages.
- Johannes Weiner has arranged for zswap memory use to be tracked and
managed on a per-cgroup basis.
- Munchun Song adds a /proc knob ("hugetlb_optimize_vmemmap") for
runtime enablement of the recent huge page vmemmap optimization
feature.
- Baolin Wang contributes a series to fix some issues around hugetlb
pagetable invalidation.
- Zhenwei Pi has fixed some interactions between hwpoisoned pages and
virtualization.
- Tong Tiangen has enabled the use of the presently x86-only
page_table_check debugging feature on arm64 and riscv.
- David Vernet has done some fixup work on the memcg selftests.
- Peter Xu has taught userfaultfd to handle write protection faults
against shmem- and hugetlbfs-backed files.
- More DAMON development from SeongJae Park - adding online tuning of
the feature and support for monitoring of fixed virtual address
ranges. Also easier discovery of which monitoring operations are
available.
- Nadav Amit has done some optimization of TLB flushing during
mprotect().
- Neil Brown continues to labor away at improving our swap-over-NFS
support.
- David Hildenbrand has some fixes to anon page COWing versus
get_user_pages().
- Peng Liu fixed some errors in the core hugetlb code.
- Joao Martins has reduced the amount of memory consumed by
device-dax's compound devmaps.
- Some cleanups of the arch-specific pagemap code from Anshuman
Khandual.
- Muchun Song has found and fixed some errors in the TLB flushing of
transparent hugepages.
- Roman Gushchin has done more work on the memcg selftests.
... and, of course, many smaller fixes and cleanups. Notably, the
customary million cleanup serieses from Miaohe Lin"
* tag 'mm-stable-2022-05-25' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (381 commits)
mm: kfence: use PAGE_ALIGNED helper
selftests: vm: add the "settings" file with timeout variable
selftests: vm: add "test_hmm.sh" to TEST_FILES
selftests: vm: check numa_available() before operating "merge_across_nodes" in ksm_tests
selftests: vm: add migration to the .gitignore
selftests/vm/pkeys: fix typo in comment
ksm: fix typo in comment
selftests: vm: add process_mrelease tests
Revert "mm/vmscan: never demote for memcg reclaim"
mm/kfence: print disabling or re-enabling message
include/trace/events/percpu.h: cleanup for "percpu: improve percpu_alloc_percpu event trace"
include/trace/events/mmflags.h: cleanup for "tracing: incorrect gfp_t conversion"
mm: fix a potential infinite loop in start_isolate_page_range()
MAINTAINERS: add Muchun as co-maintainer for HugeTLB
zram: fix Kconfig dependency warning
mm/shmem: fix shmem folio swapoff hang
cgroup: fix an error handling path in alloc_pagecache_max_30M()
mm: damon: use HPAGE_PMD_SIZE
tracing: incorrect isolate_mote_t cast in mm_vmscan_lru_isolate
nodemask.h: fix compilation error with GCC12
...
All users are now converted to release_folio
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
The basic question we would like to have a reliable and efficient answer
to is: is this anonymous page exclusive to a single process or might it be
shared? We need that information for ordinary/single pages, hugetlb
pages, and possibly each subpage of a THP.
Introduce a way to mark an anonymous page as exclusive, with the ultimate
goal of teaching our COW logic to not do "wrong COWs", whereby GUP pins
lose consistency with the pages mapped into the page table, resulting in
reported memory corruptions.
Most pageflags already have semantics for anonymous pages, however,
PG_mappedtodisk should never apply to pages in the swapcache, so let's
reuse that flag.
As PG_has_hwpoisoned also uses that flag on the second tail page of a
compound page, convert it to PG_error instead, which is marked as
PF_NO_TAIL, so never used for tail pages.
Use custom page flag modification functions such that we can do additional
sanity checks. The semantics we'll put into some kernel doc in the future
are:
"
PG_anon_exclusive is *usually* only expressive in combination with a
page table entry. Depending on the page table entry type it might
store the following information:
Is what's mapped via this page table entry exclusive to the
single process and can be mapped writable without further
checks? If not, it might be shared and we might have to COW.
For now, we only expect PTE-mapped THPs to make use of
PG_anon_exclusive in subpages. For other anonymous compound
folios (i.e., hugetlb), only the head page is logically mapped and
holds this information.
For example, an exclusive, PMD-mapped THP only has PG_anon_exclusive
set on the head page. When replacing the PMD by a page table full
of PTEs, PG_anon_exclusive, if set on the head page, will be set on
all tail pages accordingly. Note that converting from a PTE-mapping
to a PMD mapping using the same compound page is currently not
possible and consequently doesn't require care.
If GUP wants to take a reliable pin (FOLL_PIN) on an anonymous page,
it should only pin if the relevant PG_anon_exclusive is set. In that
case, the pin will be fully reliable and stay consistent with the pages
mapped into the page table, as the bit cannot get cleared (e.g., by
fork(), KSM) while the page is pinned. For anonymous pages that
are mapped R/W, PG_anon_exclusive can be assumed to always be set
because such pages cannot possibly be shared.
The page table lock protecting the page table entry is the primary
synchronization mechanism for PG_anon_exclusive; GUP-fast that does
not take the PT lock needs special care when trying to clear the
flag.
Page table entry types and PG_anon_exclusive:
* Present: PG_anon_exclusive applies.
* Swap: the information is lost. PG_anon_exclusive was cleared.
* Migration: the entry holds this information instead.
PG_anon_exclusive was cleared.
* Device private: PG_anon_exclusive applies.
* Device exclusive: PG_anon_exclusive applies.
* HW Poison: PG_anon_exclusive is stale and not changed.
If the page may be pinned (FOLL_PIN), clearing PG_anon_exclusive is
not allowed and the flag will stick around until the page is freed
and folio->mapping is cleared.
"
We won't be clearing PG_anon_exclusive on destructive unmapping (i.e.,
zapping) of page table entries, page freeing code will handle that when
also invalidate page->mapping to not indicate PageAnon() anymore. Letting
information about exclusivity stick around will be an important property
when adding sanity checks to unpinning code.
Note that we properly clear the flag in free_pages_prepare() via
PAGE_FLAGS_CHECK_AT_PREP for each individual subpage of a compound page,
so there is no need to manually clear the flag.
Link: https://lkml.kernel.org/r/20220428083441.37290-12-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The PG_waiters bit is not included in PAGE_FLAGS_CHECK_AT_FREE, and
vmscan.c's free_unref_page_list() callers rely on that not to generate
bad_page() alerts. So __page_cache_release(), put_pages_list() and
release_pages() (and presumably copy-and-pasted free_zone_device_page())
are redundant and misleading to make a special point of clearing it (as
the "__" implies, it could only safely be used on the freeing path).
Delete __ClearPageWaiters(). Remark on this in one of the "possible"
comments in folio_wake_bit(), and delete the superfluous comments.
Link: https://lkml.kernel.org/r/3eafa969-5b1a-accf-88fe-318784c791a@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Tested-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Patch series "Free the 2nd vmemmap page associated with each HugeTLB
page", v7.
This series can minimize the overhead of struct page for 2MB HugeTLB
pages significantly. It further reduces the overhead of struct page by
12.5% for a 2MB HugeTLB compared to the previous approach, which means
2GB per 1TB HugeTLB. It is a nice gain. Comments and reviews are
welcome. Thanks.
The main implementation and details can refer to the commit log of patch
1. In this series, I have changed the following four helpers, the
following table shows the impact of the overhead of those helpers.
+------------------+-----------------------+
| APIs | head page | tail page |
+------------------+-----------+-----------+
| PageHead() | Y | N |
+------------------+-----------+-----------+
| PageTail() | Y | N |
+------------------+-----------+-----------+
| PageCompound() | N | N |
+------------------+-----------+-----------+
| compound_head() | Y | N |
+------------------+-----------+-----------+
Y: Overhead is increased.
N: Overhead is _NOT_ increased.
It shows that the overhead of those helpers on a tail page don't change
between "hugetlb_free_vmemmap=on" and "hugetlb_free_vmemmap=off". But the
overhead on a head page will be increased when "hugetlb_free_vmemmap=on"
(except PageCompound()). So I believe that Matthew Wilcox's folio series
will help with this.
The users of PageHead() and PageTail() are much less than compound_head()
and most users of PageTail() are VM_BUG_ON(), so I have done some tests
about the overhead of compound_head() on head pages.
I have tested the overhead of calling compound_head() on a head page,
which is 2.11ns (Measure the call time of 10 million times
compound_head(), and then average).
For a head page whose address is not aligned with PAGE_SIZE or a
non-compound page, the overhead of compound_head() is 2.54ns which is
increased by 20%. For a head page whose address is aligned with
PAGE_SIZE, the overhead of compound_head() is 2.97ns which is increased by
40%. Most pages are the former. I do not think the overhead is
significant since the overhead of compound_head() itself is low.
This patch (of 5):
This patch minimizes the overhead of struct page for 2MB HugeTLB pages
significantly. It further reduces the overhead of struct page by 12.5%
for a 2MB HugeTLB compared to the previous approach, which means 2GB per
1TB HugeTLB (2MB type).
After the feature of "Free sonme vmemmap pages of HugeTLB page" is
enabled, the mapping of the vmemmap addresses associated with a 2MB
HugeTLB page becomes the figure below.
HugeTLB struct pages(8 pages) page frame(8 pages)
+-----------+ ---virt_to_page---> +-----------+ mapping to +-----------+---> PG_head
| | | 0 | -------------> | 0 |
| | +-----------+ +-----------+
| | | 1 | -------------> | 1 |
| | +-----------+ +-----------+
| | | 2 | ----------------^ ^ ^ ^ ^ ^
| | +-----------+ | | | | |
| | | 3 | ------------------+ | | | |
| | +-----------+ | | | |
| | | 4 | --------------------+ | | |
| 2MB | +-----------+ | | |
| | | 5 | ----------------------+ | |
| | +-----------+ | |
| | | 6 | ------------------------+ |
| | +-----------+ |
| | | 7 | --------------------------+
| | +-----------+
| |
| |
| |
+-----------+
As we can see, the 2nd vmemmap page frame (indexed by 1) is reused and
remaped. However, the 2nd vmemmap page frame is also can be freed to
the buddy allocator, then we can change the mapping from the figure
above to the figure below.
HugeTLB struct pages(8 pages) page frame(8 pages)
+-----------+ ---virt_to_page---> +-----------+ mapping to +-----------+---> PG_head
| | | 0 | -------------> | 0 |
| | +-----------+ +-----------+
| | | 1 | ---------------^ ^ ^ ^ ^ ^ ^
| | +-----------+ | | | | | |
| | | 2 | -----------------+ | | | | |
| | +-----------+ | | | | |
| | | 3 | -------------------+ | | | |
| | +-----------+ | | | |
| | | 4 | ---------------------+ | | |
| 2MB | +-----------+ | | |
| | | 5 | -----------------------+ | |
| | +-----------+ | |
| | | 6 | -------------------------+ |
| | +-----------+ |
| | | 7 | ---------------------------+
| | +-----------+
| |
| |
| |
+-----------+
After we do this, all tail vmemmap pages (1-7) are mapped to the head
vmemmap page frame (0). In other words, there are more than one page
struct with PG_head associated with each HugeTLB page. We __know__ that
there is only one head page struct, the tail page structs with PG_head are
fake head page structs. We need an approach to distinguish between those
two different types of page structs so that compound_head(), PageHead()
and PageTail() can work properly if the parameter is the tail page struct
but with PG_head.
The following code snippet describes how to distinguish between real and
fake head page struct.
if (test_bit(PG_head, &page->flags)) {
unsigned long head = READ_ONCE(page[1].compound_head);
if (head & 1) {
if (head == (unsigned long)page + 1)
==> head page struct
else
==> tail page struct
} else
==> head page struct
}
We can safely access the field of the @page[1] with PG_head because the
@page is a compound page composed with at least two contiguous pages.
[songmuchun@bytedance.com: restore lost comment changes]
Link: https://lkml.kernel.org/r/20211101031651.75851-1-songmuchun@bytedance.com
Link: https://lkml.kernel.org/r/20211101031651.75851-2-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Barry Song <song.bao.hua@hisilicon.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Chen Huang <chenhuang5@huawei.com>
Cc: Bodeddula Balasubramaniam <bodeddub@amazon.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Cc: Fam Zheng <fam.zheng@bytedance.com>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Pull more slab updates from Vlastimil Babka:
"Finish the conversion to struct slab by removing slab-specific fields
from struct page.
The first slab update (see merge commit ca1a46d6f5) did most of the
conversion, but there was also series in iommu tree removing the
iommu's usage of struct page 'freelist' field, blocking the final
struct page cleanup.
Now that the iommu changes have been merged, we can finish the job"
* tag 'slab-for-5.17-part2' of git://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab:
mm: Remove slab from struct page
Merge misc updates from Andrew Morton:
"146 patches.
Subsystems affected by this patch series: kthread, ia64, scripts,
ntfs, squashfs, ocfs2, vfs, and mm (slab-generic, slab, kmemleak,
dax, kasan, debug, pagecache, gup, shmem, frontswap, memremap,
memcg, selftests, pagemap, dma, vmalloc, memory-failure, hugetlb,
userfaultfd, vmscan, mempolicy, oom-kill, hugetlbfs, migration, thp,
ksm, page-poison, percpu, rmap, zswap, zram, cleanups, hmm, and
damon)"
* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (146 commits)
mm/damon: hide kernel pointer from tracepoint event
mm/damon/vaddr: hide kernel pointer from damon_va_three_regions() failure log
mm/damon/vaddr: use pr_debug() for damon_va_three_regions() failure logging
mm/damon/dbgfs: remove an unnecessary variable
mm/damon: move the implementation of damon_insert_region to damon.h
mm/damon: add access checking for hugetlb pages
Docs/admin-guide/mm/damon/usage: update for schemes statistics
mm/damon/dbgfs: support all DAMOS stats
Docs/admin-guide/mm/damon/reclaim: document statistics parameters
mm/damon/reclaim: provide reclamation statistics
mm/damon/schemes: account how many times quota limit has exceeded
mm/damon/schemes: account scheme actions that successfully applied
mm/damon: remove a mistakenly added comment for a future feature
Docs/admin-guide/mm/damon/usage: update for kdamond_pid and (mk|rm)_contexts
Docs/admin-guide/mm/damon/usage: mention tracepoint at the beginning
Docs/admin-guide/mm/damon/usage: remove redundant information
Docs/admin-guide/mm/damon/usage: update for scheme quotas and watermarks
mm/damon: convert macro functions to static inline functions
mm/damon: modify damon_rand() macro to static inline function
mm/damon: move damon_rand() definition into damon.h
...
After recent soft-offline rework, error pages can be taken off from
buddy allocator, but the existing unpoison_memory() does not properly
undo the operation. Moreover, due to the recent change on
__get_hwpoison_page(), get_page_unless_zero() is hardly called for
hwpoisoned pages. So __get_hwpoison_page() highly likely returns -EBUSY
(meaning to fail to grab page refcount) and unpoison just clears
PG_hwpoison without releasing a refcount. That does not lead to a
critical issue like kernel panic, but unpoisoned pages never get back to
buddy (leaked permanently), which is not good.
To (partially) fix this, we need to identify "taken off" pages from
other types of hwpoisoned pages. We can't use refcount or page flags
for this purpose, so a pseudo flag is defined by hacking ->private
field. Someone might think that put_page() is enough to cancel
taken-off pages, but the normal free path contains some operations not
suitable for the current purpose, and can fire VM_BUG_ON().
Note that unpoison_memory() is now supposed to be cancel hwpoison events
injected only by madvise() or
/sys/devices/system/memory/{hard,soft}_offline_page, not by MCE
injection, so please don't try to use unpoison when testing with MCE
injection.
[lkp@intel.com: report build failure for ARCH=i386]
Link: https://lkml.kernel.org/r/20211115084006.3728254-4-naoya.horiguchi@linux.dev
Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Ding Hui <dinghui@sangfor.com.cn>
Cc: Tony Luck <tony.luck@intel.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
All members of struct slab can now be removed from struct page.
This shrinks the definition of struct page by 30 LOC, making
it easier to understand.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
