mm: compaction: remove compaction result helpers

Patch series "mm: compaction: cleanups & simplifications".

These compaction cleanups are split out from the huge page allocator
series[1], as requested by reviewer feedback.

[1] https://lore.kernel.org/linux-mm/20230418191313.268131-1-hannes@cmpxchg.org/

This patch (of 5):

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.

Link: https://lkml.kernel.org/r/20230519123959.77335-1-hannes@cmpxchg.org
Link: https://lkml.kernel.org/r/20230519123959.77335-2-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>

diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index a6e512cfb670698d702b64cd424f535dba6d4573..1f0328a2ba485cd1cc7a381fd24d9e5ec9810070 100644 (file)
--- 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 b63e7c0fbbe5c11b63636f589af752c3a6d2b85c..1478b9dd05fae42e2c41eeee83e05d583a966b87 100644 (file)
--- 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 b9a9ba2db9e9ed006700f48b3aa5ed5830f67998..e3a3ebc2dfcece3096a8d7529c13b3225238c7e8 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3469,35 +3469,39 @@ 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