linux.git/mm/compaction.c, branch v5.9

mm: replace hpage_nr_pages with thp_nr_pages

2020-08-15T02:56:56+00:00

The thp prefix is more frequently used than hpage and we should be
consistent between the various functions.

[akpm@linux-foundation.org: fix mm/migrate.c]

Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton 
Reviewed-by: William Kucharski 
Reviewed-by: Zi Yan 
Cc: Mike Kravetz 
Cc: David Hildenbrand 
Cc: "Kirill A. Shutemov" 
Link: http://lkml.kernel.org/r/20200629151959.15779-6-willy@infradead.org
Signed-off-by: Linus Torvalds

mm/compaction.c: delete duplicated word

2020-08-12T17:57:58+00:00

Drop the repeated word "a".

Signed-off-by: Randy Dunlap 
Signed-off-by: Andrew Morton 
Reviewed-by: Andrew Morton 
Reviewed-by: Zi Yan 
Link: http://lkml.kernel.org/r/20200801173822.14973-2-rdunlap@infradead.org
Signed-off-by: Linus Torvalds

mm/compaction: correct the comments of compact_defer_shift

2020-08-12T17:57:56+00:00

There is no compact_defer_limit. It should be compact_defer_shift in
use. and add compact_order_failed explanation.

Signed-off-by: Alex Shi 
Signed-off-by: Andrew Morton 
Reviewed-by: Alexander Duyck 
Link: http://lkml.kernel.org/r/3bd60e1b-a74e-050d-ade4-6e8f54e00b92@linux.alibaba.com
Signed-off-by: Linus Torvalds

mm: use unsigned types for fragmentation score

2020-08-12T17:57:56+00:00

Proactive compaction uses per-node/zone "fragmentation score" which is
always in range [0, 100], so use unsigned type of these scores as well as
for related constants.

Signed-off-by: Nitin Gupta 
Signed-off-by: Andrew Morton 
Reviewed-by: Baoquan He 
Cc: Luis Chamberlain 
Cc: Kees Cook 
Cc: Iurii Zaikin 
Cc: Vlastimil Babka 
Cc: Joonsoo Kim 
Link: http://lkml.kernel.org/r/20200618010319.13159-1-nigupta@nvidia.com
Signed-off-by: Linus Torvalds

mm: fix compile error due to COMPACTION_HPAGE_ORDER

2020-08-12T17:57:56+00:00

Fix compile error when COMPACTION_HPAGE_ORDER is assigned to
HUGETLB_PAGE_ORDER.  The correct way to check if this constant is defined
is to check for CONFIG_HUGETLBFS.

Reported-by: Nathan Chancellor 
Signed-off-by: Nitin Gupta 
Signed-off-by: Andrew Morton 
Tested-by: Nathan Chancellor 
Cc: Stephen Rothwell 
Link: http://lkml.kernel.org/r/20200623064544.25766-1-nigupta@nvidia.com
Signed-off-by: Linus Torvalds

mm: proactive compaction

2020-08-12T17:57:56+00:00

For some applications, we need to allocate almost all memory as hugepages.
However, on a running system, higher-order allocations can fail if the
memory is fragmented.  Linux kernel currently does on-demand compaction as
we request more hugepages, but this style of compaction incurs very high
latency.  Experiments with one-time full memory compaction (followed by
hugepage allocations) show that kernel is able to restore a highly
fragmented memory state to a fairly compacted memory state within <1 sec
for a 32G system.  Such data suggests that a more proactive compaction can
help us allocate a large fraction of memory as hugepages keeping
allocation latencies low.

For a more proactive compaction, the approach taken here is to define a
new sysctl called 'vm.compaction_proactiveness' which dictates bounds for
external fragmentation which kcompactd tries to maintain.

The tunable takes a value in range [0, 100], with a default of 20.

Note that a previous version of this patch [1] was found to introduce too
many tunables (per-order extfrag{low, high}), but this one reduces them to
just one sysctl.  Also, the new tunable is an opaque value instead of
asking for specific bounds of "external fragmentation", which would have
been difficult to estimate.  The internal interpretation of this opaque
value allows for future fine-tuning.

Currently, we use a simple translation from this tunable to [low, high]
"fragmentation score" thresholds (low=100-proactiveness, high=low+10%).
The score for a node is defined as weighted mean of per-zone external
fragmentation.  A zone's present_pages determines its weight.

To periodically check per-node score, we reuse per-node kcompactd threads,
which are woken up every 500 milliseconds to check the same.  If a node's
score exceeds its high threshold (as derived from user-provided
proactiveness value), proactive compaction is started until its score
reaches its low threshold value.  By default, proactiveness is set to 20,
which implies threshold values of low=80 and high=90.

This patch is largely based on ideas from Michal Hocko [2].  See also the
LWN article [3].

Performance data
================

System: x64_64, 1T RAM, 80 CPU threads.
Kernel: 5.6.0-rc3 + this patch

echo madvise | sudo tee /sys/kernel/mm/transparent_hugepage/enabled
echo madvise | sudo tee /sys/kernel/mm/transparent_hugepage/defrag

Before starting the driver, the system was fragmented from a userspace
program that allocates all memory and then for each 2M aligned section,
frees 3/4 of base pages using munmap.  The workload is mainly anonymous
userspace pages, which are easy to move around.  I intentionally avoided
unmovable pages in this test to see how much latency we incur when
hugepage allocations hit direct compaction.

1. Kernel hugepage allocation latencies

With the system in such a fragmented state, a kernel driver then allocates
as many hugepages as possible and measures allocation latency:

(all latency values are in microseconds)

- With vanilla 5.6.0-rc3

  percentile latency
  –––––––––– –––––––
	   5    7894
	  10    9496
	  25   12561
	  30   15295
	  40   18244
	  50   21229
	  60   27556
	  75   30147
	  80   31047
	  90   32859
	  95   33799

Total 2M hugepages allocated = 383859 (749G worth of hugepages out of 762G
total free => 98% of free memory could be allocated as hugepages)

- With 5.6.0-rc3 + this patch, with proactiveness=20

sysctl -w vm.compaction_proactiveness=20

  percentile latency
  –––––––––– –––––––
	   5       2
	  10       2
	  25       3
	  30       3
	  40       3
	  50       4
	  60       4
	  75       4
	  80       4
	  90       5
	  95     429

Total 2M hugepages allocated = 384105 (750G worth of hugepages out of 762G
total free => 98% of free memory could be allocated as hugepages)

2. JAVA heap allocation

In this test, we first fragment memory using the same method as for (1).

Then, we start a Java process with a heap size set to 700G and request the
heap to be allocated with THP hugepages.  We also set THP to madvise to
allow hugepage backing of this heap.

/usr/bin/time
 java -Xms700G -Xmx700G -XX:+UseTransparentHugePages -XX:+AlwaysPreTouch

The above command allocates 700G of Java heap using hugepages.

- With vanilla 5.6.0-rc3

17.39user 1666.48system 27:37.89elapsed

- With 5.6.0-rc3 + this patch, with proactiveness=20

8.35user 194.58system 3:19.62elapsed

Elapsed time remains around 3:15, as proactiveness is further increased.

Note that proactive compaction happens throughout the runtime of these
workloads.  The situation of one-time compaction, sufficient to supply
hugepages for following allocation stream, can probably happen for more
extreme proactiveness values, like 80 or 90.

In the above Java workload, proactiveness is set to 20.  The test starts
with a node's score of 80 or higher, depending on the delay between the
fragmentation step and starting the benchmark, which gives more-or-less
time for the initial round of compaction.  As t he benchmark consumes
hugepages, node's score quickly rises above the high threshold (90) and
proactive compaction starts again, which brings down the score to the low
threshold level (80).  Repeat.

bpftrace also confirms proactive compaction running 20+ times during the
runtime of this Java benchmark.  kcompactd threads consume 100% of one of
the CPUs while it tries to bring a node's score within thresholds.

Backoff behavior
================

Above workloads produce a memory state which is easy to compact.  However,
if memory is filled with unmovable pages, proactive compaction should
essentially back off.  To test this aspect:

- Created a kernel driver that allocates almost all memory as hugepages
  followed by freeing first 3/4 of each hugepage.
- Set proactiveness=40
- Note that proactive_compact_node() is deferred maximum number of times
  with HPAGE_FRAG_CHECK_INTERVAL_MSEC of wait between each check
  (=> ~30 seconds between retries).

[1] https://patchwork.kernel.org/patch/11098289/
[2] https://lore.kernel.org/linux-mm/20161230131412.GI13301@dhcp22.suse.cz/
[3] https://lwn.net/Articles/817905/

Signed-off-by: Nitin Gupta 
Signed-off-by: Andrew Morton 
Tested-by: Oleksandr Natalenko 
Reviewed-by: Vlastimil Babka 
Reviewed-by: Khalid Aziz 
Reviewed-by: Oleksandr Natalenko 
Cc: Vlastimil Babka 
Cc: Khalid Aziz 
Cc: Michal Hocko 
Cc: Mel Gorman 
Cc: Matthew Wilcox 
Cc: Mike Kravetz 
Cc: Joonsoo Kim 
Cc: David Rientjes 
Cc: Nitin Gupta 
Cc: Oleksandr Natalenko 
Link: http://lkml.kernel.org/r/20200616204527.19185-1-nigupta@nvidia.com
Signed-off-by: Linus Torvalds

mm, compaction: make capture control handling safe wrt interrupts

2020-06-26T07:27:36+00:00

Hugh reports:

 "While stressing compaction, one run oopsed on NULL capc->cc in
  __free_one_page()'s task_capc(zone): compact_zone_order() had been
  interrupted, and a page was being freed in the return from interrupt.

  Though you would not expect it from the source, both gccs I was using
  (4.8.1 and 7.5.0) had chosen to compile compact_zone_order() with the
  ".cc = &cc" implemented by mov %rbx,-0xb0(%rbp) immediately before
  callq compact_zone - long after the "current->capture_control =
  &capc". An interrupt in between those finds capc->cc NULL (zeroed by
  an earlier rep stos).

  This could presumably be fixed by a barrier() before setting
  current->capture_control in compact_zone_order(); but would also need
  more care on return from compact_zone(), in order not to risk leaking
  a page captured by interrupt just before capture_control is reset.

  Maybe that is the preferable fix, but I felt safer for task_capc() to
  exclude the rather surprising possibility of capture at interrupt
  time"

I have checked that gcc10 also behaves the same.

The advantage of fix in compact_zone_order() is that we don't add
another test in the page freeing hot path, and that it might prevent
future problems if we stop exposing pointers to uninitialized structures
in current task.

So this patch implements the suggestion for compact_zone_order() with
barrier() (and WRITE_ONCE() to prevent store tearing) for setting
current->capture_control, and prevents page leaking with
WRITE_ONCE/READ_ONCE in the proper order.

Link: http://lkml.kernel.org/r/20200616082649.27173-1-vbabka@suse.cz
Fixes: 5e1f0f098b46 ("mm, compaction: capture a page under direct compaction")
Signed-off-by: Vlastimil Babka 
Reported-by: Hugh Dickins 
Suggested-by: Hugh Dickins 
Acked-by: Hugh Dickins 
Cc: Alex Shi 
Cc: Li Wang 
Cc: Mel Gorman 
Cc: 	[5.1+]
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/compaction: fix a typo in comment "pessemistic"->"pessimistic"

2020-06-05T02:06:23+00:00

There is a typo in comment, fix it.

Signed-off-by: Ethon Paul 
Signed-off-by: Andrew Morton 
Reviewed-by: Ralph Campbell 
Link: http://lkml.kernel.org/r/20200411070307.16021-1-ethp@qq.com
Signed-off-by: Linus Torvalds

Merge branch 'akpm' (patches from Andrew)

2020-06-04T03:24:15+00:00

Merge more updates from Andrew Morton:
 "More mm/ work, plenty more to come

  Subsystems affected by this patch series: slub, memcg, gup, kasan,
  pagealloc, hugetlb, vmscan, tools, mempolicy, memblock, hugetlbfs,
  thp, mmap, kconfig"

* akpm: (131 commits)
  arm64: mm: use ARCH_HAS_DEBUG_WX instead of arch defined
  x86: mm: use ARCH_HAS_DEBUG_WX instead of arch defined
  riscv: support DEBUG_WX
  mm: add DEBUG_WX support
  drivers/base/memory.c: cache memory blocks in xarray to accelerate lookup
  mm/thp: rename pmd_mknotpresent() as pmd_mkinvalid()
  powerpc/mm: drop platform defined pmd_mknotpresent()
  mm: thp: don't need to drain lru cache when splitting and mlocking THP
  hugetlbfs: get unmapped area below TASK_UNMAPPED_BASE for hugetlbfs
  sparc32: register memory occupied by kernel as memblock.memory
  include/linux/memblock.h: fix minor typo and unclear comment
  mm, mempolicy: fix up gup usage in lookup_node
  tools/vm/page_owner_sort.c: filter out unneeded line
  mm: swap: memcg: fix memcg stats for huge pages
  mm: swap: fix vmstats for huge pages
  mm: vmscan: limit the range of LRU type balancing
  mm: vmscan: reclaim writepage is IO cost
  mm: vmscan: determine anon/file pressure balance at the reclaim root
  mm: balance LRU lists based on relative thrashing
  mm: only count actual rotations as LRU reclaim cost
  ...

mm: rename gfpflags_to_migratetype to gfp_migratetype for same convention

2020-06-04T03:09:45+00:00

Pageblock migrate type is encoded in GFP flags, just as zone_type and
zonelist.

Currently we use gfp_zone() and gfp_zonelist() to extract related
information, it would be proper to use the same naming convention for
migrate type.

Signed-off-by: Wei Yang 
Signed-off-by: Andrew Morton 
Reviewed-by: Pankaj Gupta 
Link: http://lkml.kernel.org/r/20200329080823.7735-1-richard.weiyang@gmail.com
Signed-off-by: Linus Torvalds