On Tue 08-03-16 10:24:56, Vlastimil Babka wrote:
[...]
> > @@ -2819,28 +2819,22 @@ 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)
> > + unsigned long *compact_result)
> > {
> > - unsigned long compact_result;
> > struct page *page;
> >
> > - if (!order)
> > + if (!order) {
> > + *compact_result = COMPACT_NONE;
> > return NULL;
> > + }
> >
> > current->flags |= PF_MEMALLOC;
> > - compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac,
> > + *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_SKIPPED)
>
> COMPACT_NONE is -1 and compact_result is unsigned long, so this won't
> work as expected.
Well, COMPACT_NONE is documented as /* compaction disabled */ so we
should never get it from try_to_compact_pages.
[...]
> > @@ -3294,6 +3289,18 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> > did_some_progress > 0, no_progress_loops))
> > goto retry;
> >
> > + /*
> > + * !costly allocations are really important and we have to make sure
> > + * the compaction wasn't deferred or didn't bail out early due to locks
> > + * contention before we go OOM.
> > + */
> > + if (order && order <= PAGE_ALLOC_COSTLY_ORDER) {
> > + if (compact_result <= COMPACT_CONTINUE)
>
> Same here.
> I was going to say that this didn't have effect on Sergey's test, but
> turns out it did :)
This should work as expected because compact_result is unsigned long
and so this is the unsigned arithmetic. I can make
#define COMPACT_NONE -1UL
to make the intention more obvious if you prefer, though.
Thanks for the review.
--
Michal Hocko
SUSE Labs
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