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Message-Id: <20230519123959.77335-2-hannes@cmpxchg.org>
Date: Fri, 19 May 2023 14:39:55 +0200
From: Johannes Weiner <hannes@...xchg.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Mel Gorman <mgorman@...hsingularity.net>,
Vlastimil Babka <vbabka@...e.cz>,
Michal Hocko <mhocko@...e.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, kernel-team@...com
Subject: [PATCH 1/5] mm: compaction: remove compaction result helpers
The compaction result helpers encode quirks that are specific to the
allocator's retry logic. E.g. COMPACT_SUCCESS and COMPACT_COMPLETE
actually represent failures that should be retried upon, and so on. I
frequently found myself pulling up the helper implementation in order
to understand and work on the retry logic. They're not quite clean
abstractions; rather they split the retry logic into two locations.
Remove the helpers and inline the checks. Then comment on the result
interpretations directly where the decision making happens.
Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
include/linux/compaction.h | 92 ----------------------------------
include/trace/events/mmflags.h | 4 +-
mm/page_alloc.c | 30 ++++++-----
3 files changed, 19 insertions(+), 107 deletions(-)
diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index a6e512cfb670..1f0328a2ba48 100644
--- a/include/linux/compaction.h
+++ b/include/linux/compaction.h
@@ -95,78 +95,6 @@ extern enum compact_result compaction_suitable(struct zone *zone, int order,
extern void compaction_defer_reset(struct zone *zone, int order,
bool alloc_success);
-/* Compaction has made some progress and retrying makes sense */
-static inline bool compaction_made_progress(enum compact_result result)
-{
- /*
- * Even though this might sound confusing this in fact tells us
- * that the compaction successfully isolated and migrated some
- * pageblocks.
- */
- if (result == COMPACT_SUCCESS)
- return true;
-
- return false;
-}
-
-/* Compaction has failed and it doesn't make much sense to keep retrying. */
-static inline bool compaction_failed(enum compact_result result)
-{
- /* All zones were scanned completely and still not result. */
- if (result == COMPACT_COMPLETE)
- return true;
-
- return false;
-}
-
-/* Compaction needs reclaim to be performed first, so it can continue. */
-static inline bool compaction_needs_reclaim(enum compact_result result)
-{
- /*
- * Compaction backed off due to watermark checks for order-0
- * so the regular reclaim has to try harder and reclaim something.
- */
- if (result == COMPACT_SKIPPED)
- return true;
-
- return false;
-}
-
-/*
- * Compaction has backed off for some reason after doing some work or none
- * at all. It might be throttling or lock contention. Retrying might be still
- * worthwhile, but with a higher priority if allowed.
- */
-static inline bool compaction_withdrawn(enum compact_result result)
-{
- /*
- * If compaction is deferred for high-order allocations, it is
- * because sync compaction recently failed. If this is the case
- * and the caller requested a THP allocation, we do not want
- * to heavily disrupt the system, so we fail the allocation
- * instead of entering direct reclaim.
- */
- if (result == COMPACT_DEFERRED)
- return true;
-
- /*
- * If compaction in async mode encounters contention or blocks higher
- * priority task we back off early rather than cause stalls.
- */
- if (result == COMPACT_CONTENDED)
- return true;
-
- /*
- * Page scanners have met but we haven't scanned full zones so this
- * is a back off in fact.
- */
- if (result == COMPACT_PARTIAL_SKIPPED)
- return true;
-
- return false;
-}
-
-
bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
int alloc_flags);
@@ -185,26 +113,6 @@ static inline enum compact_result compaction_suitable(struct zone *zone, int ord
return COMPACT_SKIPPED;
}
-static inline bool compaction_made_progress(enum compact_result result)
-{
- return false;
-}
-
-static inline bool compaction_failed(enum compact_result result)
-{
- return false;
-}
-
-static inline bool compaction_needs_reclaim(enum compact_result result)
-{
- return false;
-}
-
-static inline bool compaction_withdrawn(enum compact_result result)
-{
- return true;
-}
-
static inline void kcompactd_run(int nid)
{
}
diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
index b63e7c0fbbe5..1478b9dd05fa 100644
--- a/include/trace/events/mmflags.h
+++ b/include/trace/events/mmflags.h
@@ -223,8 +223,8 @@ IF_HAVE_VM_SOFTDIRTY(VM_SOFTDIRTY, "softdirty" ) \
#define compact_result_to_feedback(result) \
({ \
enum compact_result __result = result; \
- (compaction_failed(__result)) ? COMPACTION_FAILED : \
- (compaction_withdrawn(__result)) ? COMPACTION_WITHDRAWN : COMPACTION_PROGRESS; \
+ (__result == COMPACT_COMPLETE) ? COMPACTION_FAILED : \
+ (__result == COMPACT_SUCCESS) ? COMPACTION_PROGRESS : COMPACTION_WITHDRAWN; \
})
#define COMPACTION_FEEDBACK \
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 47421bedc12b..5a84a0bebc37 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3768,35 +3768,39 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
if (fatal_signal_pending(current))
return false;
- if (compaction_made_progress(compact_result))
+ /*
+ * 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)++;
/*
- * compaction considers all the zone as desperately out of memory
- * so it doesn't really make much sense to retry except when the
+ * 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 (compaction_failed(compact_result))
+ if (compact_result == COMPACT_COMPLETE)
goto check_priority;
/*
- * compaction was skipped because there are not enough order-0 pages
- * to work with, so we retry only if it looks like reclaim can help.
+ * Compaction was skipped due to a lack of free order-0
+ * migration targets. Continue if reclaim can help.
*/
- if (compaction_needs_reclaim(compact_result)) {
+ if (compact_result == COMPACT_SKIPPED) {
ret = compaction_zonelist_suitable(ac, order, alloc_flags);
goto out;
}
/*
- * make sure the compaction wasn't deferred or didn't bail out early
- * due to locks contention before we declare that we should give up.
- * But the next retry should use a higher priority if allowed, so
- * we don't just keep bailing out endlessly.
+ * If compaction backed due to being deferred, due to
+ * contended locks in async mode, or due to scanners meeting
+ * after a partial scan, retry with increased priority.
*/
- if (compaction_withdrawn(compact_result)) {
+ if (compact_result == COMPACT_DEFERRED ||
+ compact_result == COMPACT_CONTENDED ||
+ compact_result == COMPACT_PARTIAL_SKIPPED)
goto check_priority;
- }
/*
* !costly requests are much more important than __GFP_RETRY_MAYFAIL
--
2.40.0
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