Messages in this thread | | | Date | Tue, 13 May 2014 12:00:31 +0200 | From | Vlastimil Babka <> | Subject | Re: [patch -mm] mm, thp: avoid excessive compaction latency during fault fix |
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On 05/08/2014 07:30 AM, David Rientjes wrote: > mm-thp-avoid-excessive-compaction-latency-during-fault.patch excludes sync > compaction for all high order allocations other than thp. What we really > want to do is suppress sync compaction for thp, but only during the page > fault path. > > Orders greater than PAGE_ALLOC_COSTLY_ORDER aren't necessarily going to > loop again so this is the only way to exhaust our capabilities before > declaring that we can't allocate. > > Reported-by: Hugh Dickins <hughd@google.com> > Signed-off-by: David Rientjes <rientjes@google.com> > --- > mm/page_alloc.c | 17 +++++++---------- > 1 file changed, 7 insertions(+), 10 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -2585,16 +2585,13 @@ rebalance: > if (page) > goto got_pg; > > - if (gfp_mask & __GFP_NO_KSWAPD) { > - /* > - * Khugepaged is allowed to try MIGRATE_SYNC_LIGHT, the latency > - * of this allocation isn't critical. Everything else, however, > - * should only be allowed to do MIGRATE_ASYNC to avoid excessive > - * stalls during fault. > - */ > - if ((current->flags & (PF_KTHREAD | PF_KSWAPD)) == PF_KTHREAD) > - migration_mode = MIGRATE_SYNC_LIGHT; > - } > + /* > + * 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. > + */ > + if (!(gfp_mask & __GFP_NO_KSWAPD) || (current->flags & PF_KTHREAD)) > + migration_mode = MIGRATE_SYNC_LIGHT;
I wonder what about a process doing e.g. mmap() with MAP_POPULATE. It seems to me that it would get only MIGRATE_ASYNC here, right? Since gfp_mask would include __GFP_NO_KSWAPD and it won't have PF_KTHREAD. I think that goes against the idea that with MAP_POPULATE you say you are willing to wait to have everything in place before you actually use the memory. So I guess you are also willing to wait for hugepages in that situation?
> > /* > * If compaction is deferred for high-order allocations, it is because >
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