Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753738Ab0BPGoJ (ORCPT ); Tue, 16 Feb 2010 01:44:09 -0500 Received: from cantor2.suse.de ([195.135.220.15]:46293 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753438Ab0BPGoH (ORCPT ); Tue, 16 Feb 2010 01:44:07 -0500 Date: Tue, 16 Feb 2010 17:44:02 +1100 From: Nick Piggin To: David Rientjes Cc: KAMEZAWA Hiroyuki , Andrew Morton , Rik van Riel , Andrea Arcangeli , Balbir Singh , Lubos Lunak , KOSAKI Motohiro , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [patch -mm 8/9 v2] oom: avoid oom killer for lowmem allocations Message-ID: <20100216064402.GC5723@laptop> References: <20100216085706.c7af93e1.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3326 Lines: 68 On Mon, Feb 15, 2010 at 04:10:15PM -0800, David Rientjes wrote: > 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 > > > Reviewed-by: KOSAKI Motohiro > > > Signed-off-by: David Rientjes > > > --- > > > 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. Completely agree with this request. Actually, I think even better you should just add && !(gfp_mask & __GFP_NOFAIL). Deprecated doesn't mean it is OK to break the API (callers *will* oops or corrupt memory if __GFP_NOFAIL returns NULL). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/