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mm: compaction: simplify should_compact_retry()

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The different branches for retry are unnecessarily complicated.  There are
really only three outcomes: progress (retry n times), skipped (retry if
reclaim can help), failed (retry with higher priority).

Rearrange the branches and the retry counter to make it simpler.

[hannes@cmpxchg.org: restore behavior when hitting max_retries]
  Link: https://lkml.kernel.org/r/20230602144705.GB161817@cmpxchg.org
Link: https://lkml.kernel.org/r/20230519123959.77335-3-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Johannes Weiner 2023-05-19 14:39:56 +02:00 committed by Andrew Morton
parent ecd8b2928f
commit 511a69b27f
1 changed files with 19 additions and 38 deletions
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57
mm/page_alloc.c
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@ -3469,21 +3469,6 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
if (fatal_signal_pending(current)) if (fatal_signal_pending(current))
return false; return false;
/*
* Compaction managed to coalesce some page blocks, but the
* allocation failed presumably due to a race. Retry some.
*/
if (compact_result == COMPACT_SUCCESS)
(*compaction_retries)++;
/*
* All zones were scanned completely and still no result. It
* doesn't really make much sense to retry except when the
* failure could be caused by insufficient priority
*/
if (compact_result == COMPACT_COMPLETE)
goto check_priority;
/* /*
* Compaction was skipped due to a lack of free order-0 * Compaction was skipped due to a lack of free order-0
* migration targets. Continue if reclaim can help. * migration targets. Continue if reclaim can help.
@ -3494,35 +3479,31 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
} }
/* /*
* If compaction backed due to being deferred, due to * Compaction managed to coalesce some page blocks, but the
* contended locks in async mode, or due to scanners meeting * allocation failed presumably due to a race. Retry some.
* after a partial scan, retry with increased priority.
*/ */
if (compact_result == COMPACT_DEFERRED || if (compact_result == COMPACT_SUCCESS) {
compact_result == COMPACT_CONTENDED || /*
compact_result == COMPACT_PARTIAL_SKIPPED) * !costly requests are much more important than
goto check_priority; * __GFP_RETRY_MAYFAIL costly ones because they are de
* facto nofail and invoke OOM killer to move on while
* costly can fail and users are ready to cope with
* that. 1/4 retries is rather arbitrary but we would
* need much more detailed feedback from compaction to
* make a better decision.
*/
if (order > PAGE_ALLOC_COSTLY_ORDER)
max_retries /= 4;
/* if (++(*compaction_retries) <= max_retries) {
* !costly requests are much more important than __GFP_RETRY_MAYFAIL ret = true;
* costly ones because they are de facto nofail and invoke OOM goto out;
* killer to move on while costly can fail and users are ready }
* to cope with that. 1/4 retries is rather arbitrary but we
* would need much more detailed feedback from compaction to
* make a better decision.
*/
if (order > PAGE_ALLOC_COSTLY_ORDER)
max_retries /= 4;
if (*compaction_retries <= max_retries) {
ret = true;
goto out;
} }
/* /*
* Make sure there are attempts at the highest priority if we exhausted * Compaction failed. Retry with increasing priority.
* all retries or failed at the lower priorities.
*/ */
check_priority:
min_priority = (order > PAGE_ALLOC_COSTLY_ORDER) ? min_priority = (order > PAGE_ALLOC_COSTLY_ORDER) ?
MIN_COMPACT_COSTLY_PRIORITY : MIN_COMPACT_PRIORITY; MIN_COMPACT_COSTLY_PRIORITY : MIN_COMPACT_PRIORITY;