On 07/20/2016 12:50 AM, David Rientjes wrote:
> On Mon, 18 Jul 2016, Vlastimil Babka wrote:
>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 30443804f156..a04a67745927 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -3510,7 +3510,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int
>> order,
>> struct page *page = NULL;
>> unsigned int alloc_flags;
>> unsigned long did_some_progress;
>> - enum migrate_mode migration_mode = MIGRATE_ASYNC;
>> + enum migrate_mode migration_mode = MIGRATE_SYNC_LIGHT;
>> enum compact_result compact_result;
>> int compaction_retries = 0;
>> int no_progress_loops = 0;
>> @@ -3552,6 +3552,49 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int
>> order,
>> if (page)
>> goto got_pg;
>>
>> + /*
>> + * For costly allocations, try direct compaction first, as it's likely
>> + * that we have enough base pages and don't need to reclaim.
>> + */
>> + if (can_direct_reclaim && order > PAGE_ALLOC_COSTLY_ORDER) {
>> + page = __alloc_pages_direct_compact(gfp_mask, order,
>> + alloc_flags, ac,
>> + MIGRATE_ASYNC,
>> + &compact_result);
>> + if (page)
>> + goto got_pg;
>> +
>> + /* Checks for THP-specific high-order allocations */
>> + if (is_thp_gfp_mask(gfp_mask)) {
>> + /*
>> + * 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 (compact_result == COMPACT_DEFERRED)
>> + goto nopage;
>> +
>> + /*
>> + * Compaction is contended so rather back off than cause
>> + * excessive stalls.
>> + */
>> + if (compact_result == COMPACT_CONTENDED)
>> + goto nopage;
>> +
>> + /*
>> + * It can become very expensive to allocate transparent
>> + * hugepages at fault, so use asynchronous memory
>> + * compaction for THP unless it is khugepaged trying to
>> + * collapse. All other requests should tolerate at
>> + * least light sync migration.
>> + */
>> + if (!(current->flags & PF_KTHREAD))
>> + migration_mode = MIGRATE_ASYNC;
>> + }
>> + }
>>
>
> If gfp_pfmemalloc_allowed() == true, does this try to do compaction when
> get_page_from_freelist() would have succeeded with no watermarks?
Yes, but the compaction will return immediately with COMPACT_SKIPPED, if
we are below min watermarks. So I don't think it's worth complicating
the code to avoid this?
