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Date: Mon, 15 Feb 2010 16:10:15 -0800 (PST) From: David Rientjes <rientjes@...gle.com> To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> cc: Andrew Morton <akpm@...ux-foundation.org>, Rik van Riel <riel@...hat.com>, Nick Piggin <npiggin@...e.de>, Andrea Arcangeli <aarcange@...hat.com>, Balbir Singh <balbir@...ux.vnet.ibm.com>, Lubos Lunak <l.lunak@...e.cz>, KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org Subject: Re: [patch -mm 8/9 v2] oom: avoid oom killer for lowmem allocations On Tue, 16 Feb 2010, KAMEZAWA Hiroyuki wrote: > > If memory has been depleted in lowmem zones even with the protection > > afforded to it by /proc/sys/vm/lowmem_reserve_ratio, it is unlikely that > > killing current users will help. The memory is either reclaimable (or > > migratable) already, in which case we should not invoke the oom killer at > > all, or it is pinned by an application for I/O. Killing such an > > application may leave the hardware in an unspecified state and there is > > no guarantee that it will be able to make a timely exit. > > > > Lowmem allocations are now failed in oom conditions so that the task can > > perhaps recover or try again later. Killing current is an unnecessary > > result for simply making a GFP_DMA or GFP_DMA32 page allocation and no > > lowmem allocations use the now-deprecated __GFP_NOFAIL bit so retrying is > > unnecessary. > > > > Previously, the heuristic provided some protection for those tasks with > > CAP_SYS_RAWIO, but this is no longer necessary since we will not be > > killing tasks for the purposes of ISA allocations. > > > > high_zoneidx is gfp_zone(gfp_flags), meaning that ZONE_NORMAL will be the > > default for all allocations that are not __GFP_DMA, __GFP_DMA32, > > __GFP_HIGHMEM, and __GFP_MOVABLE on kernels configured to support those > > flags. Testing for high_zoneidx being less than ZONE_NORMAL will only > > return true for allocations that have either __GFP_DMA or __GFP_DMA32. > > > > Acked-by: Rik van Riel <riel@...hat.com> > > Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> > > Signed-off-by: David Rientjes <rientjes@...gle.com> > > --- > > mm/page_alloc.c | 3 +++ > > 1 files changed, 3 insertions(+), 0 deletions(-) > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -1914,6 +1914,9 @@ rebalance: > > * running out of options and have to consider going OOM > > */ > > if (!did_some_progress) { > > + /* The oom killer won't necessarily free lowmem */ > > + if (high_zoneidx < ZONE_NORMAL) > > + goto nopage; > > if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY)) { > > if (oom_killer_disabled) > > goto nopage; > > WARN_ON((high_zoneidx < ZONE_NORMAL) && (gfp_mask & __GFP_NOFAIL)) > plz. > As I already explained when you first brought this up, the possibility of not invoking the oom killer is not unique to GFP_DMA, it is also possible for GFP_NOFS. Since __GFP_NOFAIL is deprecated and there are no current users of GFP_DMA | __GFP_NOFAIL, that warning is completely unnecessary. We're not adding any additional __GFP_NOFAIL allocations. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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