From: Michal Hocko <mhocko@xxxxxxxx>
__alloc_pages_direct_compact communicates potential back off by two
variables:
- deferred_compaction tells that the compaction returned
COMPACT_DEFERRED
- contended_compaction is set when there is a contention on
zone->lock resp. zone->lru_lock locks
__alloc_pages_slowpath then backs of for THP allocation requests to
prevent from long stalls. This is rather messy and it would be much
cleaner to return a single compact result value and hide all the nasty
details into __alloc_pages_direct_compact.
This patch shouldn't introduce any functional changes.
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
mm/page_alloc.c | 67 ++++++++++++++++++++++++++-------------------------------
1 file changed, 31 insertions(+), 36 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 42e935c83de1..c37e6d1ad643 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2944,29 +2944,21 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
static struct page *
__alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
int alloc_flags, const struct alloc_context *ac,
- enum migrate_mode mode, int *contended_compaction,
- bool *deferred_compaction)
+ enum migrate_mode mode, enum compact_result *compact_result)
{
- enum compact_result compact_result;
struct page *page;
+ int contended_compaction;
if (!order)
return NULL;
current->flags |= PF_MEMALLOC;
- compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac,
- mode, contended_compaction);
+ *compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac,
+ mode, &contended_compaction);
current->flags &= ~PF_MEMALLOC;
- switch (compact_result) {
- case COMPACT_DEFERRED:
- *deferred_compaction = true;
- /* fall-through */
- case COMPACT_SKIPPED:
+ if (*compact_result <= COMPACT_INACTIVE)
return NULL;
- default:
- break;
- }
/*
* At least in one zone compaction wasn't deferred or skipped, so let's
@@ -2992,6 +2984,24 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
*/
count_vm_event(COMPACTFAIL);
+ /*
+ * In all zones where compaction was attempted (and not
+ * deferred or skipped), lock contention has been detected.
+ * For THP allocation we do not want to disrupt the others
+ * so we fallback to base pages instead.
+ */
+ if (contended_compaction == COMPACT_CONTENDED_LOCK)
+ *compact_result = COMPACT_CONTENDED;
+
+ /*
+ * If compaction was aborted due to need_resched(), we do not
+ * want to further increase allocation latency, unless it is
+ * khugepaged trying to collapse.
+ */
+ if (contended_compaction == COMPACT_CONTENDED_SCHED
+ && !(current->flags & PF_KTHREAD))
+ *compact_result = COMPACT_CONTENDED;
+
cond_resched();
return NULL;
@@ -3000,8 +3010,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
static inline struct page *
__alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
int alloc_flags, const struct alloc_context *ac,
- enum migrate_mode mode, int *contended_compaction,
- bool *deferred_compaction)
+ enum migrate_mode mode, enum compact_result *compact_result)
{
return NULL;
}
@@ -3250,8 +3259,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
unsigned long pages_reclaimed = 0;
unsigned long did_some_progress;
enum migrate_mode migration_mode = MIGRATE_ASYNC;
- bool deferred_compaction = false;
- int contended_compaction = COMPACT_CONTENDED_NONE;
+ enum compact_result compact_result;
int no_progress_loops = 0;
/*
@@ -3350,8 +3358,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
*/
page = __alloc_pages_direct_compact(gfp_mask, order, alloc_flags, ac,
migration_mode,
- &contended_compaction,
- &deferred_compaction);
+ &compact_result);
if (page)
goto got_pg;
@@ -3364,25 +3371,14 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
* to heavily disrupt the system, so we fail the allocation
* instead of entering direct reclaim.
*/
- if (deferred_compaction)
- goto nopage;
-
- /*
- * In all zones where compaction was attempted (and not
- * deferred or skipped), lock contention has been detected.
- * For THP allocation we do not want to disrupt the others
- * so we fallback to base pages instead.
- */
- if (contended_compaction == COMPACT_CONTENDED_LOCK)
+ if (compact_result == COMPACT_DEFERRED)
goto nopage;
/*
- * If compaction was aborted due to need_resched(), we do not
- * want to further increase allocation latency, unless it is
- * khugepaged trying to collapse.
+ * Compaction is contended so rather back off than cause
+ * excessive stalls.
*/
- if (contended_compaction == COMPACT_CONTENDED_SCHED
- && !(current->flags & PF_KTHREAD))
+ if(compact_result == COMPACT_CONTENDED)
goto nopage;
}
@@ -3442,8 +3438,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
*/
page = __alloc_pages_direct_compact(gfp_mask, order, alloc_flags,
ac, migration_mode,
- &contended_compaction,
- &deferred_compaction);
+ &compact_result);
if (page)
goto got_pg;
nopage:
--
2.8.0.rc3
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