Messages in this thread | | | Subject | Re: [PATCH] mm: limit direct reclaim for higher order allocations | From | Rik van Riel <> | Date | Wed, 24 Feb 2016 17:17:56 -0500 |
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On Wed, 2016-02-24 at 14:15 -0800, David Rientjes wrote: > On Wed, 24 Feb 2016, Rik van Riel wrote: > > > For multi page allocations smaller than PAGE_ALLOC_COSTLY_ORDER, > > the kernel will do direct reclaim if compaction failed for any > > reason. This worked fine when Linux systems had 128MB RAM, but > > on my 24GB system I frequently see higher order allocations > > free up over 3GB of memory, pushing all kinds of things into > > swap, and slowing down applications. > > > > Just curious, are these higher order allocations typically done by > the > slub allocator or where are they coming from?
These are slab allocator ones, indeed.
The allocations seem to be order 2 and 3, mostly on behalf of the inode cache and alloc_skb.
> > It would be much better to limit the amount of reclaim done, > > rather than cause excessive pageout activity. > > > > When enough memory is free to do compaction for the highest order > > allocation possible, bail out of the direct page reclaim code. > > > > On smaller systems, this may be enough to obtain contiguous > > free memory areas to satisfy small allocations, continuing our > > strategy of relying on luck occasionally. On larger systems, > > relying on luck like that has not been working for years. > > > > Signed-off-by: Rik van Riel <riel@redhat.com> > > --- > > mm/vmscan.c | 19 ++++++++----------- > > 1 file changed, 8 insertions(+), 11 deletions(-) > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index fc62546096f9..8dd15d514761 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -2584,20 +2584,17 @@ static bool shrink_zones(struct zonelist > *zonelist, struct scan_control *sc) > > continue; /* Let kswapd poll it > */ > > > > /* > > - * If we already have plenty of memory free > for > > - * compaction in this zone, don't free any > more. > > - * Even though compaction is invoked for any > > - * non-zero order, only frequent costly order > > - * reclamation is disruptive enough to become > a > > - * noticeable problem, like transparent huge > > - * page allocations. > > + * For higher order allocations, free enough > memory > > + * to be able to do compaction for the > largest possible > > + * allocation. On smaller systems, this may > be enough > > + * that smaller allocations can skip > compaction, if > > + * enough adjacent pages get freed. > > */ > > - if (IS_ENABLED(CONFIG_COMPACTION) && > > - sc->order > PAGE_ALLOC_COSTLY_ORDER && > > + if (IS_ENABLED(CONFIG_COMPACTION) && sc- > >order && > > zonelist_zone_idx(z) <= requested_highidx > && > > - compaction_ready(zone, sc->order)) { > > + compaction_ready(zone, MAX_ORDER)) { > > sc->compaction_ready = true; > > - continue; > > + return true; > > } > > > > /* > > -- All Rights Reversed.
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