1. 02 Aug, 2012 6 commits
    • Mel Gorman's avatar
      mm: compaction: introduce sync-light migration for use by compaction · 4df9e193
      Mel Gorman authored
      commit a6bc32b8 upstream.
      
      Stable note: Not tracked in Buzilla. This was part of a series that
      	reduced interactivity stalls experienced when THP was enabled.
      	These stalls were particularly noticable when copying data
      	to a USB stick but the experiences for users varied a lot.
      
      This patch adds a lightweight sync migrate operation MIGRATE_SYNC_LIGHT
      mode that avoids writing back pages to backing storage.  Async compaction
      maps to MIGRATE_ASYNC while sync compaction maps to MIGRATE_SYNC_LIGHT.
      For other migrate_pages users such as memory hotplug, MIGRATE_SYNC is
      used.
      
      This avoids sync compaction stalling for an excessive length of time,
      particularly when copying files to a USB stick where there might be a
      large number of dirty pages backed by a filesystem that does not support
      ->writepages.
      
      [aarcange@redhat.com: This patch is heavily based on Andrea's work]
      [akpm@linux-foundation.org: fix fs/nfs/write.c build]
      [akpm@linux-foundation.org: fix fs/btrfs/disk-io.c build]
      Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
      Reviewed-by: default avatarRik van Riel <riel@redhat.com>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Minchan Kim <minchan.kim@gmail.com>
      Cc: Dave Jones <davej@redhat.com>
      Cc: Jan Kara <jack@suse.cz>
      Cc: Andy Isaacson <adi@hexapodia.org>
      Cc: Nai Xia <nai.xia@gmail.com>
      Cc: Johannes Weiner <jweiner@redhat.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
      4df9e193
    • Mel Gorman's avatar
      mm: compaction: make isolate_lru_page() filter-aware again · 34c8ed43
      Mel Gorman authored
      commit c8244935 upstream.
      
      Stable note: Not tracked in Bugzilla. A fix aimed at preserving page aging
      	information by reducing LRU list churning had the side-effect of
      	reducing THP allocation success rates. This was part of a series
      	to restore the success rates while preserving the reclaim fix.
      
      Commit 39deaf85 ("mm: compaction: make isolate_lru_page() filter-aware")
      noted that compaction does not migrate dirty or writeback pages and that
      is was meaningless to pick the page and re-add it to the LRU list.  This
      had to be partially reverted because some dirty pages can be migrated by
      compaction without blocking.
      
      This patch updates "mm: compaction: make isolate_lru_page" by skipping
      over pages that migration has no possibility of migrating to minimise LRU
      disruption.
      Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
      Reviewed-by: Rik van Riel<riel@redhat.com>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Reviewed-by: default avatarMinchan Kim <minchan@kernel.org>
      Cc: Dave Jones <davej@redhat.com>
      Cc: Jan Kara <jack@suse.cz>
      Cc: Andy Isaacson <adi@hexapodia.org>
      Cc: Nai Xia <nai.xia@gmail.com>
      Cc: Johannes Weiner <jweiner@redhat.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
      34c8ed43
    • Mel Gorman's avatar
      mm: page allocator: do not call direct reclaim for THP allocations while compaction is deferred · e9a127ba
      Mel Gorman authored
      commit 66199712 upstream.
      
      Stable note: Not tracked in Buzilla. This was part of a series that
      	reduced interactivity stalls experienced when THP was enabled.
      
      If compaction is deferred, direct reclaim is used to try to free enough
      pages for the allocation to succeed.  For small high-orders, this has a
      reasonable chance of success.  However, if the caller has specified
      __GFP_NO_KSWAPD to limit the disruption to the system, it makes more sense
      to fail the allocation rather than stall the caller in direct reclaim.
      This patch skips direct reclaim if compaction is deferred and the caller
      specifies __GFP_NO_KSWAPD.
      
      Async compaction only considers a subset of pages so it is possible for
      compaction to be deferred prematurely and not enter direct reclaim even in
      cases where it should.  To compensate for this, this patch also defers
      compaction only if sync compaction failed.
      Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
      Acked-by: default avatarMinchan Kim <minchan.kim@gmail.com>
      Reviewed-by: Rik van Riel<riel@redhat.com>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dave Jones <davej@redhat.com>
      Cc: Jan Kara <jack@suse.cz>
      Cc: Andy Isaacson <adi@hexapodia.org>
      Cc: Nai Xia <nai.xia@gmail.com>
      Cc: Johannes Weiner <jweiner@redhat.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
      e9a127ba
    • Mel Gorman's avatar
      mm: compaction: determine if dirty pages can be migrated without blocking within ->migratepage · 41927678
      Mel Gorman authored
      commit b969c4ab upstream.
      
      Stable note: Not tracked in Bugzilla. A fix aimed at preserving page
      	aging information by reducing LRU list churning had the side-effect
      	of reducing THP allocation success rates. This was part of a series
      	to restore the success rates while preserving the reclaim fix.
      
      Asynchronous compaction is used when allocating transparent hugepages to
      avoid blocking for long periods of time.  Due to reports of stalling,
      there was a debate on disabling synchronous compaction but this severely
      impacted allocation success rates.  Part of the reason was that many dirty
      pages are skipped in asynchronous compaction by the following check;
      
      	if (PageDirty(page) && !sync &&
      		mapping->a_ops->migratepage != migrate_page)
      			rc = -EBUSY;
      
      This skips over all mapping aops using buffer_migrate_page() even though
      it is possible to migrate some of these pages without blocking.  This
      patch updates the ->migratepage callback with a "sync" parameter.  It is
      the responsibility of the callback to fail gracefully if migration would
      block.
      Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
      Reviewed-by: default avatarRik van Riel <riel@redhat.com>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Minchan Kim <minchan.kim@gmail.com>
      Cc: Dave Jones <davej@redhat.com>
      Cc: Jan Kara <jack@suse.cz>
      Cc: Andy Isaacson <adi@hexapodia.org>
      Cc: Nai Xia <nai.xia@gmail.com>
      Cc: Johannes Weiner <jweiner@redhat.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
      41927678
    • Mel Gorman's avatar
      mm: compaction: allow compaction to isolate dirty pages · 46aadfff
      Mel Gorman authored
      commit a77ebd33 upstream.
      
      Stable note: Not tracked in Bugzilla. A fix aimed at preserving page aging
      	information by reducing LRU list churning had the side-effect of
      	reducing THP allocation success rates. This was part of a series
      	to restore the success rates while preserving the reclaim fix.
      
      Short summary: There are severe stalls when a USB stick using VFAT is
      used with THP enabled that are reduced by this series.  If you are
      experiencing this problem, please test and report back and considering I
      have seen complaints from openSUSE and Fedora users on this as well as a
      few private mails, I'm guessing it's a widespread issue.  This is a new
      type of USB-related stall because it is due to synchronous compaction
      writing where as in the past the big problem was dirty pages reaching
      the end of the LRU and being written by reclaim.
      
      Am cc'ing Andrew this time and this series would replace
      mm-do-not-stall-in-synchronous-compaction-for-thp-allocations.patch.
      I'm also cc'ing Dave Jones as he might have merged that patch to Fedora
      for wider testing and ideally it would be reverted and replaced by this
      series.
      
      That said, the later patches could really do with some review.  If this
      series is not the answer then a new direction needs to be discussed
      because as it is, the stalls are unacceptable as the results in this
      leader show.
      
      For testers that try backporting this to 3.1, it won't work because
      there is a non-obvious dependency on not writing back pages in direct
      reclaim so you need those patches too.
      
      Changelog since V5
      o Rebase to 3.2-rc5
      o Tidy up the changelogs a bit
      
      Changelog since V4
      o Added reviewed-bys, credited Andrea properly for sync-light
      o Allow dirty pages without mappings to be considered for migration
      o Bound the number of pages freed for compaction
      o Isolate PageReclaim pages on their own LRU list
      
      This is against 3.2-rc5 and follows on from discussions on "mm: Do
      not stall in synchronous compaction for THP allocations" and "[RFC
      PATCH 0/5] Reduce compaction-related stalls". Initially, the proposed
      patch eliminated stalls due to compaction which sometimes resulted in
      user-visible interactivity problems on browsers by simply never using
      sync compaction. The downside was that THP success allocation rates
      were lower because dirty pages were not being migrated as reported by
      Andrea. His approach at fixing this was nacked on the grounds that
      it reverted fixes from Rik merged that reduced the amount of pages
      reclaimed as it severely impacted his workloads performance.
      
      This series attempts to reconcile the requirements of maximising THP
      usage, without stalling in a user-visible fashion due to compaction
      or cheating by reclaiming an excessive number of pages.
      
      Patch 1 partially reverts commit 39deaf85 to allow migration to isolate
      	dirty pages. This is because migration can move some dirty
      	pages without blocking.
      
      Patch 2 notes that the /proc/sys/vm/compact_memory handler is not using
      	synchronous compaction when it should be. This is unrelated
      	to the reported stalls but is worth fixing.
      
      Patch 3 checks if we isolated a compound page during lumpy scan and
      	account for it properly. For the most part, this affects
      	tracing so it's unrelated to the stalls but worth fixing.
      
      Patch 4 notes that it is possible to abort reclaim early for compaction
      	and return 0 to the page allocator potentially entering the
      	"may oom" path. This has not been observed in practice but
      	the rest of the series potentially makes it easier to happen.
      
      Patch 5 adds a sync parameter to the migratepage callback and gives
      	the callback responsibility for migrating the page without
      	blocking if sync==false. For example, fallback_migrate_page
      	will not call writepage if sync==false. This increases the
      	number of pages that can be handled by asynchronous compaction
      	thereby reducing stalls.
      
      Patch 6 restores filter-awareness to isolate_lru_page for migration.
      	In practice, it means that pages under writeback and pages
      	without a ->migratepage callback will not be isolated
      	for migration.
      
      Patch 7 avoids calling direct reclaim if compaction is deferred but
      	makes sure that compaction is only deferred if sync
      	compaction was used.
      
      Patch 8 introduces a sync-light migration mechanism that sync compaction
      	uses. The objective is to allow some stalls but to not call
      	->writepage which can lead to significant user-visible stalls.
      
      Patch 9 notes that while we want to abort reclaim ASAP to allow
      	compation to go ahead that we leave a very small window of
      	opportunity for compaction to run. This patch allows more pages
      	to be freed by reclaim but bounds the number to a reasonable
      	level based on the high watermark on each zone.
      
      Patch 10 allows slabs to be shrunk even after compaction_ready() is
      	true for one zone. This is to avoid a problem whereby a single
      	small zone can abort reclaim even though no pages have been
      	reclaimed and no suitably large zone is in a usable state.
      
      Patch 11 fixes a problem with the rate of page scanning. As reclaim is
      	rarely stalling on pages under writeback it means that scan
      	rates are very high. This is particularly true for direct
      	reclaim which is not calling writepage. The vmstat figures
      	implied that much of this was busy work with PageReclaim pages
      	marked for immediate reclaim. This patch is a prototype that
      	moves these pages to their own LRU list.
      
      This has been tested and other than 2 USB keys getting trashed,
      nothing horrible fell out. That said, I am a bit unhappy with the
      rescue logic in patch 11 but did not find a better way around it. It
      does significantly reduce scan rates and System CPU time indicating
      it is the right direction to take.
      
      What is of critical importance is that stalls due to compaction
      are massively reduced even though sync compaction was still
      allowed. Testing from people complaining about stalls copying to USBs
      with THP enabled are particularly welcome.
      
      The following tests all involve THP usage and USB keys in some
      way. Each test follows this type of pattern
      
      1. Read from some fast fast storage, be it raw device or file. Each time
         the copy finishes, start again until the test ends
      2. Write a large file to a filesystem on a USB stick. Each time the copy
         finishes, start again until the test ends
      3. When memory is low, start an alloc process that creates a mapping
         the size of physical memory to stress THP allocation. This is the
         "real" part of the test and the part that is meant to trigger
         stalls when THP is enabled. Copying continues in the background.
      4. Record the CPU usage and time to execute of the alloc process
      5. Record the number of THP allocs and fallbacks as well as the number of THP
         pages in use a the end of the test just before alloc exited
      6. Run the test 5 times to get an idea of variability
      7. Between each run, sync is run and caches dropped and the test
         waits until nr_dirty is a small number to avoid interference
         or caching between iterations that would skew the figures.
      
      The individual tests were then
      
      writebackCPDeviceBasevfat
      	Disable THP, read from a raw device (sda), vfat on USB stick
      writebackCPDeviceBaseext4
      	Disable THP, read from a raw device (sda), ext4 on USB stick
      writebackCPDevicevfat
      	THP enabled, read from a raw device (sda), vfat on USB stick
      writebackCPDeviceext4
      	THP enabled, read from a raw device (sda), ext4 on USB stick
      writebackCPFilevfat
      	THP enabled, read from a file on fast storage and USB, both vfat
      writebackCPFileext4
      	THP enabled, read from a file on fast storage and USB, both ext4
      
      The kernels tested were
      
      3.1		3.1
      vanilla		3.2-rc5
      freemore	Patches 1-10
      immediate	Patches 1-11
      andrea		The 8 patches Andrea posted as a basis of comparison
      
      The results are very long unfortunately. I'll start with the case
      where we are not using THP at all
      
      writebackCPDeviceBasevfat
                         3.1.0-vanilla         rc5-vanilla       freemore-v6r1        isolate-v6r1         andrea-v2r1
      System Time         1.28 (    0.00%)   54.49 (-4143.46%)   48.63 (-3687.69%)    4.69 ( -265.11%)   51.88 (-3940.81%)
      +/-                 0.06 (    0.00%)    2.45 (-4305.55%)    4.75 (-8430.57%)    7.46 (-13282.76%)    4.76 (-8440.70%)
      User Time           0.09 (    0.00%)    0.05 (   40.91%)    0.06 (   29.55%)    0.07 (   15.91%)    0.06 (   27.27%)
      +/-                 0.02 (    0.00%)    0.01 (   45.39%)    0.02 (   25.07%)    0.00 (   77.06%)    0.01 (   52.24%)
      Elapsed Time      110.27 (    0.00%)   56.38 (   48.87%)   49.95 (   54.70%)   11.77 (   89.33%)   53.43 (   51.54%)
      +/-                 7.33 (    0.00%)    3.77 (   48.61%)    4.94 (   32.63%)    6.71 (    8.50%)    4.76 (   35.03%)
      THP Active          0.00 (    0.00%)    0.00 (    0.00%)    0.00 (    0.00%)    0.00 (    0.00%)    0.00 (    0.00%)
      +/-                 0.00 (    0.00%)    0.00 (    0.00%)    0.00 (    0.00%)    0.00 (    0.00%)    0.00 (    0.00%)
      Fault Alloc         0.00 (    0.00%)    0.00 (    0.00%)    0.00 (    0.00%)    0.00 (    0.00%)    0.00 (    0.00%)
      +/-                 0.00 (    0.00%)    0.00 (    0.00%)    0.00 (    0.00%)    0.00 (    0.00%)    0.00 (    0.00%)
      Fault Fallback      0.00 (    0.00%)    0.00 (    0.00%)    0.00 (    0.00%)    0.00 (    0.00%)    0.00 (    0.00%)
      +/-                 0.00 (    0.00%)    0.00 (    0.00%)    0.00 (    0.00%)    0.00 (    0.00%)    0.00 (    0.00%)
      
      The THP figures are obviously all 0 because THP was enabled. The
      main thing to watch is the elapsed times and how they compare to
      times when THP is enabled later. It's also important to note that
      elapsed time is improved by this series as System CPu time is much
      reduced.
      
      writebackCPDevicevfat
      
                         3.1.0-vanilla         rc5-vanilla       freemore-v6r1        isolate-v6r1         andrea-v2r1
      System Time         1.22 (    0.00%)   13.89 (-1040.72%)   46.40 (-3709.20%)    4.44 ( -264.37%)   47.37 (-3789.33%)
      +/-                 0.06 (    0.00%)   22.82 (-37635.56%)    3.84 (-6249.44%)    6.48 (-10618.92%)    6.60
      (-10818.53%)
      User Time           0.06 (    0.00%)    0.06 (   -6.90%)    0.05 (   17.24%)    0.05 (   13.79%)    0.04 (   31.03%)
      +/-                 0.01 (    0.00%)    0.01 (   33.33%)    0.01 (   33.33%)    0.01 (   39.14%)    0.01 (   25.46%)
      Elapsed Time     10445.54 (    0.00%) 2249.92 (   78.46%)   70.06 (   99.33%)   16.59 (   99.84%)  472.43 (
      95.48%)
      +/-               643.98 (    0.00%)  811.62 (  -26.03%)   10.02 (   98.44%)    7.03 (   98.91%)   59.99 (   90.68%)
      THP Active         15.60 (    0.00%)   35.20 (  225.64%)   65.00 (  416.67%)   70.80 (  453.85%)   62.20 (  398.72%)
      +/-                18.48 (    0.00%)   51.29 (  277.59%)   15.99 (   86.52%)   37.91 (  205.18%)   22.02 (  119.18%)
      Fault Alloc       121.80 (    0.00%)   76.60 (   62.89%)  155.40 (  127.59%)  181.20 (  148.77%)  286.60 (  235.30%)
      +/-                73.51 (    0.00%)   61.11 (   83.12%)   34.89 (   47.46%)   31.88 (   43.36%)   68.13 (   92.68%)
      Fault Fallback    881.20 (    0.00%)  926.60 (   -5.15%)  847.60 (    3.81%)  822.00 (    6.72%)  716.60 (   18.68%)
      +/-                73.51 (    0.00%)   61.26 (   16.67%)   34.89 (   52.54%)   31.65 (   56.94%)   67.75 (    7.84%)
      MMTests Statistics: duration
      User/Sys Time Running Test (seconds)       3540.88   1945.37    716.04     64.97   1937.03
      Total Elapsed Time (seconds)              52417.33  11425.90    501.02    230.95   2520.28
      
      The first thing to note is the "Elapsed Time" for the vanilla kernels
      of 2249 seconds versus 56 with THP disabled which might explain the
      reports of USB stalls with THP enabled. Applying the patches brings
      performance in line with THP-disabled performance while isolating
      pages for immediate reclaim from the LRU cuts down System CPU time.
      
      The "Fault Alloc" success rate figures are also improved. The vanilla
      kernel only managed to allocate 76.6 pages on average over the course
      of 5 iterations where as applying the series allocated 181.20 on
      average albeit it is well within variance. It's worth noting that
      applies the series at least descreases the amount of variance which
      implies an improvement.
      
      Andrea's series had a higher success rate for THP allocations but
      at a severe cost to elapsed time which is still better than vanilla
      but still much worse than disabling THP altogether. One can bring my
      series close to Andrea's by removing this check
      
              /*
               * If compaction is deferred for high-order allocations, it is because
               * sync compaction recently failed. In this is the case and the caller
               * has requested the system not be heavily disrupted, fail the
               * allocation now instead of entering direct reclaim
               */
              if (deferred_compaction && (gfp_mask & __GFP_NO_KSWAPD))
                      goto nopage;
      
      I didn't include a patch that removed the above check because hurting
      overall performance to improve the THP figure is not what the average
      user wants. It's something to consider though if someone really wants
      to maximise THP usage no matter what it does to the workload initially.
      
      This is summary of vmstat figures from the same test.
      
                                             3.1.0-vanilla rc5-vanilla freemore-v6r1 isolate-v6r1 andrea-v2r1
      Page Ins                                  3257266139  1111844061    17263623    10901575   161423219
      Page Outs                                   81054922    30364312     3626530     3657687     8753730
      Swap Ins                                        3294        2851        6560        4964        4592
      Swap Outs                                     390073      528094      620197      790912      698285
      Direct pages scanned                      1077581700  3024951463  1764930052   115140570  5901188831
      Kswapd pages scanned                        34826043     7112868     2131265     1686942     1893966
      Kswapd pages reclaimed                      28950067     4911036     1246044      966475     1497726
      Direct pages reclaimed                     805148398   280167837     3623473     2215044    40809360
      Kswapd efficiency                                83%         69%         58%         57%         79%
      Kswapd velocity                              664.399     622.521    4253.852    7304.360     751.490
      Direct efficiency                                74%          9%          0%          1%          0%
      Direct velocity                            20557.737  264745.137 3522673.849  498551.938 2341481.435
      Percentage direct scans                          96%         99%         99%         98%         99%
      Page writes by reclaim                        722646      529174      620319      791018      699198
      Page writes file                              332573        1080         122         106         913
      Page writes anon                              390073      528094      620197      790912      698285
      Page reclaim immediate                             0  2552514720  1635858848   111281140  5478375032
      Page rescued immediate                             0           0           0       87848           0
      Slabs scanned                                  23552       23552        9216        8192        9216
      Direct inode steals                              231           0           0           0           0
      Kswapd inode steals                                0           0           0           0           0
      Kswapd skipped wait                            28076         786           0          61           6
      THP fault alloc                                  609         383         753         906        1433
      THP collapse alloc                                12           6           0           0           6
      THP splits                                       536         211         456         593        1136
      THP fault fallback                              4406        4633        4263        4110        3583
      THP collapse fail                                120         127           0           0           4
      Compaction stalls                               1810         728         623         779        3200
      Compaction success                               196          53          60          80         123
      Compaction failures                             1614         675         563         699        3077
      Compaction pages moved                        193158       53545      243185      333457      226688
      Compaction move failure                         9952        9396       16424       23676       45070
      
      The main things to look at are
      
      1. Page In/out figures are much reduced by the series.
      
      2. Direct page scanning is incredibly high (264745.137 pages scanned
         per second on the vanilla kernel) but isolating PageReclaim pages
         on their own list reduces the number of pages scanned significantly.
      
      3. The fact that "Page rescued immediate" is a positive number implies
         that we sometimes race removing pages from the LRU_IMMEDIATE list
         that need to be put back on a normal LRU but it happens only for
         0.07% of the pages marked for immediate reclaim.
      
      writebackCPDeviceext4
                         3.1.0-vanilla         rc5-vanilla       freemore-v6r1        isolate-v6r1         andrea-v2r1
      System Time         1.51 (    0.00%)    1.77 (  -17.66%)    1.46 (    2.92%)    1.15 (   23.77%)    1.89 (  -25.63%)
      +/-                 0.27 (    0.00%)    0.67 ( -148.52%)    0.33 (  -22.76%)    0.30 (  -11.15%)    0.19 (   30.16%)
      User Time           0.03 (    0.00%)    0.04 (  -37.50%)    0.05 (  -62.50%)    0.07 ( -112.50%)    0.04 (  -18.75%)
      +/-                 0.01 (    0.00%)    0.02 ( -146.64%)    0.02 (  -97.91%)    0.02 (  -75.59%)    0.02 (  -63.30%)
      Elapsed Time      124.93 (    0.00%)  114.49 (    8.36%)   96.77 (   22.55%)   27.48 (   78.00%)  205.70 (  -64.65%)
      +/-                20.20 (    0.00%)   74.39 ( -268.34%)   59.88 ( -196.48%)    7.72 (   61.79%)   25.03 (  -23.95%)
      THP Active        161.80 (    0.00%)   83.60 (   51.67%)  141.20 (   87.27%)   84.60 (   52.29%)   82.60 (   51.05%)
      +/-                71.95 (    0.00%)   43.80 (   60.88%)   26.91 (   37.40%)   59.02 (   82.03%)   52.13 (   72.45%)
      Fault Alloc       471.40 (    0.00%)  228.60 (   48.49%)  282.20 (   59.86%)  225.20 (   47.77%)  388.40 (   82.39%)
      +/-                88.07 (    0.00%)   87.42 (   99.26%)   73.79 (   83.78%)  109.62 (  124.47%)   82.62 (   93.81%)
      Fault Fallback    531.60 (    0.00%)  774.60 (  -45.71%)  720.80 (  -35.59%)  777.80 (  -46.31%)  614.80 (  -15.65%)
      +/-                88.07 (    0.00%)   87.26 (    0.92%)   73.79 (   16.22%)  109.62 (  -24.47%)   82.29 (    6.56%)
      MMTests Statistics: duration
      User/Sys Time Running Test (seconds)         50.22     33.76     30.65     24.14    128.45
      Total Elapsed Time (seconds)               1113.73   1132.19   1029.45    759.49   1707.26
      
      Similar test but the USB stick is using ext4 instead of vfat. As
      ext4 does not use writepage for migration, the large stalls due to
      compaction when THP is enabled are not observed. Still, isolating
      PageReclaim pages on their own list helped completion time largely
      by reducing the number of pages scanned by direct reclaim although
      time spend in congestion_wait could also be a factor.
      
      Again, Andrea's series had far higher success rates for THP allocation
      at the cost of elapsed time. I didn't look too closely but a quick
      look at the vmstat figures tells me kswapd reclaimed 8 times more pages
      than the patch series and direct reclaim reclaimed roughly three times
      as many pages. It follows that if memory is aggressively reclaimed,
      there will be more available for THP.
      
      writebackCPFilevfat
                         3.1.0-vanilla         rc5-vanilla       freemore-v6r1        isolate-v6r1         andrea-v2r1
      System Time         1.76 (    0.00%)   29.10 (-1555.52%)   46.01 (-2517.18%)    4.79 ( -172.35%)   54.89 (-3022.53%)
      +/-                 0.14 (    0.00%)   25.61 (-18185.17%)    2.15 (-1434.83%)    6.60 (-4610.03%)    9.75
      (-6863.76%)
      User Time           0.05 (    0.00%)    0.07 (  -45.83%)    0.05 (   -4.17%)    0.06 (  -29.17%)    0.06 (  -16.67%)
      +/-                 0.02 (    0.00%)    0.02 (   20.11%)    0.02 (   -3.14%)    0.01 (   31.58%)    0.01 (   47.41%)
      Elapsed Time     22520.79 (    0.00%) 1082.85 (   95.19%)   73.30 (   99.67%)   32.43 (   99.86%)  291.84 (  98.70%)
      +/-              7277.23 (    0.00%)  706.29 (   90.29%)   19.05 (   99.74%)   17.05 (   99.77%)  125.55 (   98.27%)
      THP Active         83.80 (    0.00%)   12.80 (   15.27%)   15.60 (   18.62%)   13.00 (   15.51%)    0.80 (    0.95%)
      +/-                66.81 (    0.00%)   20.19 (   30.22%)    5.92 (    8.86%)   15.06 (   22.54%)    1.17 (    1.75%)
      Fault Alloc       171.00 (    0.00%)   67.80 (   39.65%)   97.40 (   56.96%)  125.60 (   73.45%)  133.00 (   77.78%)
      +/-                82.91 (    0.00%)   30.69 (   37.02%)   53.91 (   65.02%)   55.05 (   66.40%)   21.19 (   25.56%)
      Fault Fallback    832.00 (    0.00%)  935.20 (  -12.40%)  906.00 (   -8.89%)  877.40 (   -5.46%)  870.20 (   -4.59%)
      +/-                82.91 (    0.00%)   30.69 (   62.98%)   54.01 (   34.86%)   55.05 (   33.60%)   20.91 (   74.78%)
      MMTests Statistics: duration
      User/Sys Time Running Test (seconds)       7229.81    928.42    704.52     80.68   1330.76
      Total Elapsed Time (seconds)             112849.04   5618.69    571.11    360.54   1664.28
      
      In this case, the test is reading/writing only from filesystems but as
      it's vfat, it's slow due to calling writepage during compaction. Little
      to observe really - the time to complete the test goes way down
      with the series applied and THP allocation success rates go up in
      comparison to 3.2-rc5.  The success rates are lower than 3.1.0 but
      the elapsed time for that kernel is abysmal so it is not really a
      sensible comparison.
      
      As before, Andrea's series allocates more THPs at the cost of overall
      performance.
      
      writebackCPFileext4
                         3.1.0-vanilla         rc5-vanilla       freemore-v6r1        isolate-v6r1         andrea-v2r1
      System Time         1.51 (    0.00%)    1.77 (  -17.66%)    1.46 (    2.92%)    1.15 (   23.77%)    1.89 (  -25.63%)
      +/-                 0.27 (    0.00%)    0.67 ( -148.52%)    0.33 (  -22.76%)    0.30 (  -11.15%)    0.19 (   30.16%)
      User Time           0.03 (    0.00%)    0.04 (  -37.50%)    0.05 (  -62.50%)    0.07 ( -112.50%)    0.04 (  -18.75%)
      +/-                 0.01 (    0.00%)    0.02 ( -146.64%)    0.02 (  -97.91%)    0.02 (  -75.59%)    0.02 (  -63.30%)
      Elapsed Time      124.93 (    0.00%)  114.49 (    8.36%)   96.77 (   22.55%)   27.48 (   78.00%)  205.70 (  -64.65%)
      +/-                20.20 (    0.00%)   74.39 ( -268.34%)   59.88 ( -196.48%)    7.72 (   61.79%)   25.03 (  -23.95%)
      THP Active        161.80 (    0.00%)   83.60 (   51.67%)  141.20 (   87.27%)   84.60 (   52.29%)   82.60 (   51.05%)
      +/-                71.95 (    0.00%)   43.80 (   60.88%)   26.91 (   37.40%)   59.02 (   82.03%)   52.13 (   72.45%)
      Fault Alloc       471.40 (    0.00%)  228.60 (   48.49%)  282.20 (   59.86%)  225.20 (   47.77%)  388.40 (   82.39%)
      +/-                88.07 (    0.00%)   87.42 (   99.26%)   73.79 (   83.78%)  109.62 (  124.47%)   82.62 (   93.81%)
      Fault Fallback    531.60 (    0.00%)  774.60 (  -45.71%)  720.80 (  -35.59%)  777.80 (  -46.31%)  614.80 (  -15.65%)
      +/-                88.07 (    0.00%)   87.26 (    0.92%)   73.79 (   16.22%)  109.62 (  -24.47%)   82.29 (    6.56%)
      MMTests Statistics: duration
      User/Sys Time Running Test (seconds)         50.22     33.76     30.65     24.14    128.45
      Total Elapsed Time (seconds)               1113.73   1132.19   1029.45    759.49   1707.26
      
      Same type of story - elapsed times go down. In this case, allocation
      success rates are roughtly the same. As before, Andrea's has higher
      success rates but takes a lot longer.
      
      Overall the series does reduce latencies and while the tests are
      inherency racy as alloc competes with the cp processes, the variability
      was included. The THP allocation rates are not as high as they could
      be but that is because we would have to be more aggressive about
      reclaim and compaction impacting overall performance.
      
      This patch:
      
      Commit 39deaf85 ("mm: compaction: make isolate_lru_page() filter-aware")
      noted that compaction does not migrate dirty or writeback pages and that
      is was meaningless to pick the page and re-add it to the LRU list.
      
      What was missed during review is that asynchronous migration moves dirty
      pages if their ->migratepage callback is migrate_page() because these can
      be moved without blocking.  This potentially impacted hugepage allocation
      success rates by a factor depending on how many dirty pages are in the
      system.
      
      This patch partially reverts 39deaf85 to allow migration to isolate dirty
      pages again.  This increases how much compaction disrupts the LRU but that
      is addressed later in the series.
      Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
      Reviewed-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
      Reviewed-by: default avatarRik van Riel <riel@redhat.com>
      Reviewed-by: default avatarMinchan Kim <minchan.kim@gmail.com>
      Cc: Dave Jones <davej@redhat.com>
      Cc: Jan Kara <jack@suse.cz>
      Cc: Andy Isaacson <adi@hexapodia.org>
      Cc: Nai Xia <nai.xia@gmail.com>
      Cc: Johannes Weiner <jweiner@redhat.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
      46aadfff
    • Mel Gorman's avatar
      mm: reduce the amount of work done when updating min_free_kbytes · c653414d
      Mel Gorman authored
      commit 938929f1 upstream.
      
      Stable note: Fixes https://bugzilla.novell.com/show_bug.cgi?id=726210 .
              Large machines with 1TB or more of RAM take a long time to boot
              without this patch and may spew out soft lockup warnings.
      
      When min_free_kbytes is updated, some pageblocks are marked
      MIGRATE_RESERVE.  Ordinarily, this work is unnoticable as it happens early
      in boot but on large machines with 1TB of memory, this has been reported
      to delay boot times, probably due to the NUMA distances involved.
      
      The bulk of the work is due to calling calling pageblock_is_reserved() an
      unnecessary amount of times and accessing far more struct page metadata
      than is necessary.  This patch significantly reduces the amount of work
      done by setup_zone_migrate_reserve() improving boot times on 1TB machines.
      
      [akpm@linux-foundation.org: coding-style fixes]
      Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
      c653414d
  2. 25 Jul, 2012 34 commits