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mm: page_alloc: close migratetype race between freeing and stealing

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There are three freeing paths that read the page's migratetype
optimistically before grabbing the zone lock.  When this races with block
stealing, those pages go on the wrong freelist.

The paths in question are:
- when freeing >costly orders that aren't THP
- when freeing pages to the buddy upon pcp lock contention
- when freeing pages that are isolated
- when freeing pages initially during boot
- when freeing the remainder in alloc_pages_exact()
- when "accepting" unaccepted VM host memory before first use
- when freeing pages during unpoisoning

None of these are so hot that they would need this optimization at the
cost of hampering defrag efforts.  Especially when contrasted with the
fact that the most common buddy freeing path - free_pcppages_bulk - is
checking the migratetype under the zone->lock just fine.

In addition, isolated pages need to look up the migratetype under the lock
anyway, which adds branches to the locked section, and results in a double
lookup when the pages are in fact isolated.

Move the lookups into the lock.

Link: https://lkml.kernel.org/r/20240320180429.678181-8-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reported-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Johannes Weiner 2024-03-20 14:02:12 -04:00 • committed by Andrew Morton
commit 55612e80e7
1 changed files with 19 additions and 33 deletions
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