patches/kernel/0019-revert-mm-compatction-fix-set-skip-in.patch

   1 From 025cbf4866306fe4823e8c316c20bdaddc6a0340 Mon Sep 17 00:00:00 2001
   2 From: Vlastimil Babka <vbabka@suse.cz>
   3 Date: Fri, 13 Jan 2023 18:33:45 +0100
   4 Subject: Revert "mm/compaction: fix set skip in fast_find_migrateblock"
   5
   6 commit 95e7a450b8190673675836bfef236262ceff084a upstream.
   7
   8 This reverts commit 7efc3b7261030da79001c00d92bc3392fd6c664c.
   9
  10 We have got openSUSE reports (Link 1) for 6.1 kernel with khugepaged
  11 stalling CPU for long periods of time.  Investigation of tracepoint data
  12 shows that compaction is stuck in repeating fast_find_migrateblock()
  13 based migrate page isolation, and then fails to migrate all isolated
  14 pages.
  15
  16 Commit 7efc3b726103 ("mm/compaction: fix set skip in fast_find_migrateblock")
  17 was suspected as it was merged in 6.1 and in theory can indeed remove a
  18 termination condition for fast_find_migrateblock() under certain
  19 conditions, as it removes a place that always marks a scanned pageblock
  20 from being re-scanned.  There are other such places, but those can be
  21 skipped under certain conditions, which seems to match the tracepoint
  22 data.
  23
  24 Testing of revert also appears to have resolved the issue, thus revert
  25 the commit until a more robust solution for the original problem is
  26 developed.
  27
  28 It's also likely this will fix qemu stalls with 6.1 kernel reported in
  29 Link 2, but that is not yet confirmed.
  30
  31 Link: https://bugzilla.suse.com/show_bug.cgi?id=1206848
  32 Link: https://lore.kernel.org/kvm/b8017e09-f336-3035-8344-c549086c2340@kernel.org/
  33 Link: https://lore.kernel.org/lkml/20230125134434.18017-1-mgorman@techsingularity.net/
  34 Fixes: 7efc3b726103 ("mm/compaction: fix set skip in fast_find_migrateblock")
  35 Cc: <stable@vger.kernel.org>
  36 Tested-by: Pedro Falcato <pedro.falcato@gmail.com>
  37 Acked-by: Mel Gorman <mgorman@techsingularity.net>
  38 Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
  39 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  40 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  41 ---
  42  mm/compaction.c | 1 +
  43  1 file changed, 1 insertion(+)
  44
  45 diff --git a/mm/compaction.c b/mm/compaction.c
  46 index ca1603524bbe0..8238e83385a79 100644
  47 --- a/mm/compaction.c
  48 +++ b/mm/compaction.c
  49 @@ -1839,6 +1839,7 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc)
  50                                         pfn = cc->zone->zone_start_pfn;
  51                                 cc->fast_search_fail = 0;
  52                                 found_block = true;
  53 +                               set_pageblock_skip(freepage);
  54                                 break;
  55                         }
  56                 }
  57 --
  58 cgit