On Tue, 7 Oct 2014 17:33:36 +0200 Vlastimil Babka <vbabka@xxxxxxx> wrote:
> Since commit ("mm, compaction: defer each zone individually instead of
> preferred zone"), compaction is deferred for each zone where sync direct
> compaction fails, and reset where it succeeds. However, it was observed
> that for DMA zone compaction often appeared to succeed while subsequent
> allocation attempt would not, due to different outcome of watermark check.
> In order to properly defer compaction in this zone, the candidate zone has
> to be passed back to __alloc_pages_direct_compact() and compaction deferred
> in the zone after the allocation attempt fails.
>
> The large source of mismatch between watermark check in compaction and
> allocation was the lack of alloc_flags and classzone_idx values in compaction,
> which has been fixed in the previous patch. So with this problem fixed, we
> can simplify the code by removing the candidate_zone parameter and deferring
> in __alloc_pages_direct_compact().
>
> After this patch, the compaction activity during stress-highalloc benchmark is
> still somewhat increased, but it's negligible compared to the increase that
> occurred without the better watermark checking. This suggests that it is still
> possible to apparently succeed in compaction but fail to allocate, possibly
> due to parallel allocation activity.
>
> ...
>
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -33,8 +33,7 @@ extern int fragmentation_index(struct zone *zone, unsigned int order);
> extern unsigned long try_to_compact_pages(struct zonelist *zonelist,
> int order, gfp_t gfp_mask, nodemask_t *mask,
> enum migrate_mode mode, int *contended,
> - int alloc_flags, int classzone_idx,
> - struct zone **candidate_zone);
> + int alloc_flags, int classzone_idx);
> extern void compact_pgdat(pg_data_t *pgdat, int order);
> extern void reset_isolation_suitable(pg_data_t *pgdat);
> extern unsigned long compaction_suitable(struct zone *zone, int order,
> @@ -105,8 +104,7 @@ static inline bool compaction_restarting(struct zone *zone, int order)
> static inline unsigned long try_to_compact_pages(struct zonelist *zonelist,
> int order, gfp_t gfp_mask, nodemask_t *nodemask,
> enum migrate_mode mode, int *contended,
> - int alloc_flags, int classzone_idx,
> - struct zone **candidate_zone)
> + int alloc_flags, int classzone_idx);
> {
> return COMPACT_CONTINUE;
> }
--- a/include/linux/compaction.h~mm-compaction-simplify-deferred-compaction-fix
+++ a/include/linux/compaction.h
@@ -104,7 +104,7 @@ static inline bool compaction_restarting
static inline unsigned long try_to_compact_pages(struct zonelist *zonelist,
int order, gfp_t gfp_mask, nodemask_t *nodemask,
enum migrate_mode mode, int *contended,
- int alloc_flags, int classzone_idx);
+ int alloc_flags, int classzone_idx)
{
return COMPACT_CONTINUE;
}
It clearly wasn't tested with this config. Please do so and let us
know the result?
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