Compaction returns prematurely with COMPACT_PARTIAL when contended or has
fatal signal pending. This is ok for the callers, but might be misleading
in the traces, as the usual reason to return COMPACT_PARTIAL is that we
think the allocation should succeed. After this patch we distinguish the
premature ending condition in the mm_compaction_finished and
mm_compaction_end tracepoints.
The contended status covers the following reasons:
- lock contention or need_resched() detected in async compaction
- fatal signal pending
- too many pages isolated in the zone (only for async compaction)
Further distinguishing the exact reason seems unnecessary for now.
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Some compaction tracepoints convert the integer return values to strings
using the compaction_status_string array. This works for in-kernel
printing, but not userspace trace printing of raw captured trace such as
via trace-cmd report.
This patch converts the private array to appropriate tracepoint macros
that result in proper userspace support.
trace-cmd output before:
transhuge-stres-4235 [000] 453.149280: mm_compaction_finished: node=0
zone=ffffffff81815d7a order=9 ret=
after:
transhuge-stres-4235 [000] 453.149280: mm_compaction_finished: node=0
zone=ffffffff81815d7a order=9 ret=partial
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Introduce is_via_compact_memory() helper indicating compacting via
/proc/sys/vm/compact_memory to improve readability.
To catch this situation in __compaction_suitable, use order as parameter
directly instead of using struct compact_control.
This patch has no functional changes.
Signed-off-by: Yaowei Bai <bywxiaobai@163.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
We cache isolate_start_pfn before entering isolate_migratepages(). If
pageblock is skipped in isolate_migratepages() due to whatever reason,
cc->migrate_pfn can be far from isolate_start_pfn hence we flush pages
that were freed. For example, the following scenario can be possible:
- assume order-9 compaction, pageblock order is 9
- start_isolate_pfn is 0x200
- isolate_migratepages()
- skip a number of pageblocks
- start to isolate from pfn 0x600
- cc->migrate_pfn = 0x620
- return
- last_migrated_pfn is set to 0x200
- check flushing condition
- current_block_start is set to 0x600
- last_migrated_pfn < current_block_start then do useless flush
This wrong flush would not help the performance and success rate so this
patch tries to fix it. One simple way to know the exact position where
we start to isolate migratable pages is that we cache it in
isolate_migratepages() before entering actual isolation. This patch
implements that and fixes the problem.
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The compaction free scanner is looking for PageBuddy() pages and
skipping all others. For large compound pages such as THP or hugetlbfs,
we can save a lot of iterations if we skip them at once using their
compound_order(). This is generally unsafe and we can read a bogus
value of order due to a race, but if we are careful, the only danger is
skipping too much.
When tested with stress-highalloc from mmtests on 4GB system with 1GB
hugetlbfs pages, the vmstat compact_free_scanned count decreased by at
least 15%.
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The compaction migrate scanner tries to skip THP pages by their order,
to reduce number of iterations for pages it cannot isolate. The check
is only done if PageLRU() is true, which means it applies to THP pages,
but not e.g. hugetlbfs pages or any other non-LRU compound pages, which
we have to iterate by base pages.
This limitation comes from the assumption that it's only safe to read
compound_order() when we have the zone's lru_lock and THP cannot be
split under us. But the only danger (after filtering out order values
that are not below MAX_ORDER, to prevent overflows) is that we skip too
much or too little after reading a bogus compound_order() due to a rare
race. This is the same reasoning as patch 99c0fd5e51 ("mm,
compaction: skip buddy pages by their order in the migrate scanner")
introduced for unsafely reading PageBuddy() order.
After this patch, all pages are tested for PageCompound() and we skip
them by compound_order(). The test is done after the test for
balloon_page_movable() as we don't want to assume if balloon pages (or
other pages with own isolation and migration implementation if a generic
API gets implemented) are compound or not.
When tested with stress-highalloc from mmtests on 4GB system with 1GB
hugetlbfs pages, the vmstat compact_migrate_scanned count decreased by
15%.
[kirill.shutemov@linux.intel.com: change PageTransHuge checks to PageCompound for different series was squashed here]
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Minchan Kim <minchan@kernel.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Handling the position where compaction free scanner should restart
(stored in cc->free_pfn) got more complex with commit e14c720efd ("mm,
compaction: remember position within pageblock in free pages scanner").
Currently the position is updated in each loop iteration of
isolate_freepages(), although it should be enough to update it only when
breaking from the loop. There's also an extra check outside the loop
updates the position in case we have met the migration scanner.
This can be simplified if we move the test for having isolated enough
from the for-loop header next to the test for contention, and
determining the restart position only in these cases. We can reuse the
isolate_start_pfn variable for this instead of setting cc->free_pfn
directly. Outside the loop, we can simply set cc->free_pfn to current
value of isolate_start_pfn without any extra check.
Also add a VM_BUG_ON to catch possible mistake in the future, in case we
later add a new condition that terminates isolate_freepages_block()
prematurely without also considering the condition in
isolate_freepages().
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Minchan Kim <minchan@kernel.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Assorted compaction cleanups and optimizations. The interesting patches
are 4 and 5. In 4, skipping of compound pages in single iteration is
improved for migration scanner, so it works also for !PageLRU compound
pages such as hugetlbfs, slab etc. Patch 5 introduces this kind of
skipping in the free scanner. The trick is that we can read
compound_order() without any protection, if we are careful to filter out
values larger than MAX_ORDER. The only danger is that we skip too much.
The same trick was already used for reading the freepage order in the
migrate scanner.
To demonstrate improvements of Patches 4 and 5 I've run stress-highalloc
from mmtests, set to simulate THP allocations (including __GFP_COMP) on
a 4GB system where 1GB was occupied by hugetlbfs pages. I'll include
just the relevant stats:
Patch 3 Patch 4 Patch 5
Compaction stalls 7523 7529 7515
Compaction success 323 304 322
Compaction failures 7200 7224 7192
Page migrate success 247778 264395 240737
Page migrate failure 15358 33184 21621
Compaction pages isolated 906928 980192 909983
Compaction migrate scanned 2005277 1692805 1498800
Compaction free scanned 13255284 11539986 9011276
Compaction cost 288 305 277
With 5 iterations per patch, the results are still noisy, but we can see
that Patch 4 does reduce migrate_scanned by 15% thanks to skipping the
hugetlbfs pages at once. Interestingly, free_scanned is also reduced
and I have no idea why. Patch 5 further reduces free_scanned as
expected, by 15%. Other stats are unaffected modulo noise.
[1] https://lkml.org/lkml/2015/1/19/158
This patch (of 5):
Compaction should finish when the migration and free scanner meet, i.e.
they reach the same pageblock. Currently however, the test in
compact_finished() simply just compares the exact pfns, which may yield
a false negative when the free scanner position is in the middle of a
pageblock and the migration scanner reaches the begining of the same
pageblock.
This hasn't been a problem until commit e14c720efd ("mm, compaction:
remember position within pageblock in free pages scanner") allowed the
free scanner position to be in the middle of a pageblock between
invocations. The hot-fix 1d5bfe1ffb ("mm, compaction: prevent
infinite loop in compact_zone") prevented the issue by adding a special
check in the migration scanner to satisfy the current detection of
scanners meeting.
However, the proper fix is to make the detection more robust. This
patch introduces the compact_scanners_met() function that returns true
when the free scanner position is in the same or lower pageblock than
the migration scanner. The special case in isolate_migratepages()
introduced by 1d5bfe1ffb is removed.
Suggested-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Minchan Kim <minchan@kernel.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Christoph Lameter <cl@linux.com>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
When the compaction is activated via /proc/sys/vm/compact_memory it would
better scan the whole zone. And some platforms, for instance ARM, have
the start_pfn of a zone at zero. Therefore the first try to compact via
/proc doesn't work. It needs to reset the compaction scanner position
first.
Signed-off-by: Gioh Kim <gioh.kim@lge.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Currently, pages which are marked as unevictable are protected from
compaction, but not from other types of migration. The POSIX real time
extension explicitly states that mlock() will prevent a major page
fault, but the spirit of this is that mlock() should give a process the
ability to control sources of latency, including minor page faults.
However, the mlock manpage only explicitly says that a locked page will
not be written to swap and this can cause some confusion. The
compaction code today does not give a developer who wants to avoid swap
but wants to have large contiguous areas available any method to achieve
this state. This patch introduces a sysctl for controlling compaction
behavior with respect to the unevictable lru. Users who demand no page
faults after a page is present can set compact_unevictable_allowed to 0
and users who need the large contiguous areas can enable compaction on
locked memory by leaving the default value of 1.
To illustrate this problem I wrote a quick test program that mmaps a
large number of 1MB files filled with random data. These maps are
created locked and read only. Then every other mmap is unmapped and I
attempt to allocate huge pages to the static huge page pool. When the
compact_unevictable_allowed sysctl is 0, I cannot allocate hugepages
after fragmenting memory. When the value is set to 1, allocations
succeed.
Signed-off-by: Eric B Munson <emunson@akamai.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Christoph Lameter <cl@linux.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Christoph Lameter <cl@linux.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Compaction has anti fragmentation algorithm. It is that freepage should
be more than pageblock order to finish the compaction if we don't find any
freepage in requested migratetype buddy list. This is for mitigating
fragmentation, but, there is a lack of migratetype consideration and it is
too excessive compared to page allocator's anti fragmentation algorithm.
Not considering migratetype would cause premature finish of compaction.
For example, if allocation request is for unmovable migratetype, freepage
with CMA migratetype doesn't help that allocation and compaction should
not be stopped. But, current logic regards this situation as compaction
is no longer needed, so finish the compaction.
Secondly, condition is too excessive compared to page allocator's logic.
We can steal freepage from other migratetype and change pageblock
migratetype on more relaxed conditions in page allocator. This is
designed to prevent fragmentation and we can use it here. Imposing hard
constraint only to the compaction doesn't help much in this case since
page allocator would cause fragmentation again.
To solve these problems, this patch borrows anti fragmentation logic from
page allocator. It will reduce premature compaction finish in some cases
and reduce excessive compaction work.
stress-highalloc test in mmtests with non movable order 7 allocation shows
considerable increase of compaction success rate.
Compaction success rate (Compaction success * 100 / Compaction stalls, %)
31.82 : 42.20
I tested it on non-reboot 5 runs stress-highalloc benchmark and found that
there is no more degradation on allocation success rate than before. That
roughly means that this patch doesn't result in more fragmentations.
Vlastimil suggests additional idea that we only test for fallbacks when
migration scanner has scanned a whole pageblock. It looked good for
fragmentation because chance of stealing increase due to making more free
pages in certain pageblock. So, I tested it, but, it results in decreased
compaction success rate, roughly 38.00. I guess the reason that if system
is low memory condition, watermark check could be failed due to not enough
order 0 free page and so, sometimes, we can't reach a fallback check
although migrate_pfn is aligned to pageblock_nr_pages. I can insert code
to cope with this situation but it makes code more complicated so I don't
include his idea at this patch.
[akpm@linux-foundation.org: fix CONFIG_CMA=n build]
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The vmstat interfaces are good at hiding negative counts (at least when
CONFIG_SMP); but if you peer behind the curtain, you find that
nr_isolated_anon and nr_isolated_file soon go negative, and grow ever
more negative: so they can absorb larger and larger numbers of isolated
pages, yet still appear to be zero.
I'm happy to avoid a congestion_wait() when too_many_isolated() myself;
but I guess it's there for a good reason, in which case we ought to get
too_many_isolated() working again.
The imbalance comes from isolate_migratepages()'s ISOLATE_ABORT case:
putback_movable_pages() decrements the NR_ISOLATED counts, but we forgot
to call acct_isolated() to increment them.
It is possible that the bug whcih this patch fixes could cause OOM kills
when the system still has a lot of reclaimable page cache.
Fixes: edc2ca6124 ("mm, compaction: move pageblock checks up from isolate_migratepages_range()")
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: <stable@vger.kernel.org> [3.18+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Currently, freepage isolation in one pageblock doesn't consider how many
freepages we isolate. When I traced flow of compaction, compaction
sometimes isolates more than 256 freepages to migrate just 32 pages.
In this patch, freepage isolation is stopped at the point that we
have more isolated freepage than isolated page for migration. This
results in slowing down free page scanner and make compaction success
rate higher.
stress-highalloc test in mmtests with non movable order 7 allocation shows
increase of compaction success rate.
Compaction success rate (Compaction success * 100 / Compaction stalls, %)
27.13 : 31.82
pfn where both scanners meets on compaction complete
(separate test due to enormous tracepoint buffer)
(zone_start=4096, zone_end=1048576)
586034 : 654378
In fact, I didn't fully understand why this patch results in such good
result. There was a guess that not used freepages are released to pcp list
and on next compaction trial we won't isolate them again so compaction
success rate would decrease. To prevent this effect, I tested with adding
pcp drain code on release_freepages(), but, it has no good effect.
Anyway, this patch reduces waste time to isolate unneeded freepages so
seems reasonable.
Vlastimil said:
: I briefly tried it on top of the pivot-changing series and with order-9
: allocations it reduced free page scanned counter by almost 10%. No effect
: on success rates (maybe because pivot changing already took care of the
: scanners meeting problem) but the scanning reduction is good on its own.
:
: It also explains why e14c720efd ("mm, compaction: remember position
: within pageblock in free pages scanner") had less than expected
: improvements. It would only actually stop within pageblock in case of
: async compaction detecting contention. I guess that's also why the
: infinite loop problem fixed by 1d5bfe1ffb affected so relatively few
: people.
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
What we want to check here is whether there is highorder freepage in buddy
list of other migratetype in order to steal it without fragmentation.
But, current code just checks cc->order which means allocation request
order. So, this is wrong.
Without this fix, non-movable synchronous compaction below pageblock order
would not stopped until compaction is complete, because migratetype of
most pageblocks are movable and high order freepage made by compaction is
usually on movable type buddy list.
There is some report related to this bug. See below link.
http://www.spinics.net/lists/linux-mm/msg81666.html
Although the issued system still has load spike comes from compaction,
this makes that system completely stable and responsive according to his
report.
stress-highalloc test in mmtests with non movable order 7 allocation
doesn't show any notable difference in allocation success rate, but, it
shows more compaction success rate.
Compaction success rate (Compaction success * 100 / Compaction stalls, %)
18.47 : 28.94
Fixes: 1fb3f8ca0e ("mm: compaction: capture a suitable high-order page immediately when it is made available")
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: <stable@vger.kernel.org> [3.7+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Compaction deferring logic is heavy hammer that block the way to the
compaction. It doesn't consider overall system state, so it could prevent
user from doing compaction falsely. In other words, even if system has
enough range of memory to compact, compaction would be skipped due to
compaction deferring logic. This patch add new tracepoint to understand
work of deferring logic. This will also help to check compaction success
and fail.
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
It'd be useful to know current range where compaction work for detailed
analysis. With it, we can know pageblock where we actually scan and
isolate, and, how much pages we try in that pageblock and can guess why it
doesn't become freepage with pageblock order roughly.
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
We now have tracepoint for begin event of compaction and it prints start
position of both scanners, but, tracepoint for end event of compaction
doesn't print finish position of both scanners. It'd be also useful to
know finish position of both scanners so this patch add it. It will help
to find odd behavior or problem on compaction internal logic.
And mode is added to both begin/end tracepoint output, since according to
mode, compaction behavior is quite different.
And lastly, status format is changed to string rather than status number
for readability.
[akpm@linux-foundation.org: fix sparse warning]
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Expand the usage of the struct alloc_context introduced in the previous
patch also for calling try_to_compact_pages(), to reduce the number of its
parameters. Since the function is in different compilation unit, we need
to move alloc_context definition in the shared mm/internal.h header.
With this change we get simpler code and small savings of code size and stack
usage:
add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-27 (-27)
function old new delta
__alloc_pages_direct_compact 283 256 -27
add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-13 (-13)
function old new delta
try_to_compact_pages 582 569 -13
Stack usage of __alloc_pages_direct_compact goes from 24 to none (per
scripts/checkstack.pl).
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The goal of memory compaction is to create high-order freepages through
page migration. Page migration however puts pages on the per-cpu lru_add
cache, which is later flushed to per-cpu pcplists, and only after pcplists
are drained the pages can actually merge. This can happen due to the
per-cpu caches becoming full through further freeing, or explicitly.
During direct compaction, it is useful to do the draining explicitly so
that pages merge as soon as possible and compaction can detect success
immediately and keep the latency impact at minimum. However the current
implementation is far from ideal. Draining is done only in
__alloc_pages_direct_compact(), after all zones were already compacted,
and the decisions to continue or stop compaction in individual zones was
done without the last batch of migrations being merged. It is also
missing the draining of lru_add cache before the pcplists.
This patch moves the draining for direct compaction into compact_zone().
It adds the missing lru_cache draining and uses the newly introduced
single zone pcplists draining to reduce overhead and avoid impact on
unrelated zones. Draining is only performed when it can actually lead to
merging of a page of desired order (passed by cc->order). This means it
is only done when migration occurred in the previously scanned cc->order
aligned block(s) and the migration scanner is now pointing to the next
cc->order aligned block.
The patch has been tested with stress-highalloc benchmark from mmtests.
Although overal allocation success rates of the benchmark were not
affected, the number of detected compaction successes has doubled. This
suggests that allocations were previously successful due to implicit
merging caused by background activity, making a later allocation attempt
succeed immediately, but not attributing the success to compaction. Since
stress-highalloc always tries to allocate almost the whole memory, it
cannot show the improvement in its reported success rate metric. However
after this patch, compaction should detect success and terminate earlier,
reducing the direct compaction latencies in a real scenario.
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Christoph Lameter <cl@linux.com>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Compaction caches the migration and free scanner positions between
compaction invocations, so that the whole zone gets eventually scanned and
there is no bias towards the initial scanner positions at the
beginning/end of the zone.
The cached positions are continuously updated as scanners progress and the
updating stops as soon as a page is successfully isolated. The reasoning
behind this is that a pageblock where isolation succeeded is likely to
succeed again in near future and it should be worth revisiting it.
However, the downside is that potentially many pages are rescanned without
successful isolation. At worst, there might be a page where isolation
from LRU succeeds but migration fails (potentially always). So upon
encountering this page, cached position would always stop being updated
for no good reason. It might have been useful to let such page be
rescanned with sync compaction after async one failed, but this is now
handled by caching scanner position for async and sync mode separately
since commit 35979ef339 ("mm, compaction: add per-zone migration pfn
cache for async compaction").
After this patch, cached positions are updated unconditionally. In
stress-highalloc benchmark, this has decreased the numbers of scanned
pages by few percent, without affecting allocation success rates.
To prevent free scanner from leaving free pages behind after they are
returned due to page migration failure, the cached scanner pfn is changed
to point to the pageblock of the returned free page with the highest pfn,
before leaving compact_zone().
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Christoph Lameter <cl@linux.com>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Deferred compaction is employed to avoid compacting zone where sync direct
compaction has recently failed. As such, it makes sense to only defer
when a full zone was scanned, which is when compact_zone returns with
COMPACT_COMPLETE. It's less useful to defer when compact_zone returns
with apparent success (COMPACT_PARTIAL), followed by a watermark check
failure, which can happen due to parallel allocation activity. It also
does not make much sense to defer compaction which was completely skipped
(COMPACT_SKIP) for being unsuitable in the first place.
This patch therefore makes deferred compaction trigger only when
COMPACT_COMPLETE is returned from compact_zone(). Results of
stress-highalloc becnmark show the difference is within measurement error,
so the issue is rather cosmetic.
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Christoph Lameter <cl@linux.com>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Vlastimil Babka
Yaowei Bai
Joonsoo Kim
Andrew Morton
Gioh Kim
Eric B Munson
Andrey Ryabinin
Hugh Dickins