+ mm-page_alloc-bail-out-on-fatal-signal-during-reclaim-compaction-retry-attempt.patch added to -mm tree

+ mm-page_alloc-bail-out-on-fatal-signal-during-reclaim-compaction-retry-attempt.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm/page_alloc: bail out on fatal signal during reclaim/compaction retry attempt
has been added to the -mm tree.  Its filename is
     mm-page_alloc-bail-out-on-fatal-signal-during-reclaim-compaction-retry-attempt.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-page_alloc-bail-out-on-fatal-signal-during-reclaim-compaction-retry-attempt.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-page_alloc-bail-out-on-fatal-signal-during-reclaim-compaction-retry-attempt.patch

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------------------------------------------------------
From: Aaron Tomlin <atomlin@redhat.com>
Subject: mm/page_alloc: bail out on fatal signal during reclaim/compaction retry attempt

A customer experienced a low-memory situation and decided to issue a
SIGKILL (i.e.  a fatal signal).  Instead of promptly terminating as one
would expect, the aforementioned task remained unresponsive.

Further investigation indicated that the task was "stuck" in the
reclaim/compaction retry loop.  Now, it does not make sense to retry
compaction when a fatal signal is pending.

In the context of try_to_compact_pages(), indeed COMPACT_SKIPPED can be
returned; albeit, not every zone, on the zone list, would be considered in
the case a fatal signal is found to be pending.  Yet, in
should_compact_retry(), given the last known compaction result, each zone,
on the zone list, can be considered/or checked (see
compaction_zonelist_suitable()).  For example, if a zone was found to
succeed, then reclaim/compaction would be tried again (notwithstanding the
above).

This patch ensures that compaction is not needlessly retried irrespective
of the last known compaction result e.g.  if it was skipped, in the
unlikely case a fatal signal is found pending.  So, OOM is at least
attempted.

Link: https://lkml.kernel.org/r/20210520142901.3371299-1-atomlin@redhat.com
Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page_alloc.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/mm/page_alloc.c~mm-page_alloc-bail-out-on-fatal-signal-during-reclaim-compaction-retry-attempt
+++ a/mm/page_alloc.c
@@ -4251,6 +4251,9 @@ should_compact_retry(struct alloc_contex
 	if (!order)
 		return false;
 
+	if (fatal_signal_pending(current))
+		return false;
+
 	if (compaction_made_progress(compact_result))
 		(*compaction_retries)++;
 
_

Patches currently in -mm which might be from atomlin@redhat.com are

mm-page_alloc-bail-out-on-fatal-signal-during-reclaim-compaction-retry-attempt.patch