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Yu Zhao 30d77b7eef mm/mglru: fix ineffective protection calculation
mem_cgroup_calculate_protection() is not stateless and should only be used
as part of a top-down tree traversal.  shrink_one() traverses the per-node
memcg LRU instead of the root_mem_cgroup tree, and therefore it should not
call mem_cgroup_calculate_protection().

The existing misuse in shrink_one() can cause ineffective protection of
sub-trees that are grandchildren of root_mem_cgroup.  Fix it by reusing
lru_gen_age_node(), which already traverses the root_mem_cgroup tree, to
calculate the protection.

Previously lru_gen_age_node() opportunistically skips the first pass,
i.e., when scan_control->priority is DEF_PRIORITY.  On the second pass,
lruvec_is_sizable() uses appropriate scan_control->priority, set by
set_initial_priority() from lru_gen_shrink_node(), to decide whether a
memcg is too small to reclaim from.

Now lru_gen_age_node() unconditionally traverses the root_mem_cgroup tree.
So it should call set_initial_priority() upfront, to make sure
lruvec_is_sizable() uses appropriate scan_control->priority on the first
pass.  Otherwise, lruvec_is_reclaimable() can return false negatives and
result in premature OOM kills when min_ttl_ms is used.

Link: https://lkml.kernel.org/r/20240712232956.1427127-1-yuzhao@google.com
Fixes: e4dde56cd2 ("mm: multi-gen LRU: per-node lru_gen_folio lists")
Signed-off-by: Yu Zhao <yuzhao@google.com>
Reported-by: T.J. Mercier <tjmercier@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
History 2024-07-17 21:08:55 -07:00
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Linux kernel
============

There are several guides for kernel developers and users. These guides can
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In order to build the documentation, use ``make htmldocs`` or
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There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
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the problems which may result by upgrading your kernel.