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whatawurst / android_kernel_sony_msm8998

LineageOS Kernel Tree for Sony Xperia XZ Premium, XZ1 and XZ1 Compact
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zsmalloc: account the number of compacted pages correctly #70

Closed Amy07i closed 2 years ago

Amy07i commented 2 years ago

commit 2395928158059b8f9858365fce7713ce7fef62e4 upstream.

There exists multiple path may do zram compaction concurrently.

  1. auto-compaction triggered during memory reclaim
  2. userspace utils write zram/compaction node

So, multiple threads may call zs_shrinker_scan/zs_compact concurrently. But pages_compacted is a per zsmalloc pool variable and modification of the variable is not serialized(through under class->lock). There are two issues here:

  1. the pages_compacted may not equal to total number of pages freed(due to concurrently add).
  2. zs_shrinker_scan may not return the correct number of pages freed(issued by current shrinker).

The fix is simple:

  1. account the number of pages freed in zs_compact locally.
  2. use actomic variable pages_compacted to accumulate total number.

Link: https://lkml.kernel.org/r/20210202122235.26885-1-wu-yan@tcl.com Fixes: 860c707dca155a56 ("zsmalloc: account the number of compacted pages") Signed-off-by: Rokudo Yan wu-yan@tcl.com Cc: Minchan Kim minchan@kernel.org Cc: Sergey Senozhatsky sergey.senozhatsky@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

Amy07i commented 2 years ago

Not merged in v4.4.260 because of commit c1a8b1eba761cc52443cf0d4a28e26745206fc80.

derfelot commented 2 years ago

Thanks, I must have forgotten to check when I reverted that change for the z3fold implementation. I suppose you checked if there was anything else missing?