From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756385AbbHZSKw (ORCPT ); Wed, 26 Aug 2015 14:10:52 -0400 Received: from outbound-smtp02.blacknight.com ([81.17.249.8]:50271 "EHLO outbound-smtp02.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751797AbbHZSKv (ORCPT ); Wed, 26 Aug 2015 14:10:51 -0400 Date: Wed, 26 Aug 2015 19:10:41 +0100 From: Mel Gorman To: Vlastimil Babka Cc: Andrew Morton , Johannes Weiner , Rik van Riel , David Rientjes , Joonsoo Kim , Michal Hocko , Linux-MM , LKML Subject: Re: [PATCH 07/12] mm, page_alloc: Distinguish between being unable to sleep, unwilling to sleep and avoiding waking kswapd Message-ID: <20150826181041.GR12432@techsingularity.net> References: <1440418191-10894-1-git-send-email-mgorman@techsingularity.net> <1440418191-10894-8-git-send-email-mgorman@techsingularity.net> <55DC8BD7.602@suse.cz> <20150826144533.GO12432@techsingularity.net> <55DDE842.8000103@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <55DDE842.8000103@suse.cz> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 26, 2015 at 06:24:34PM +0200, Vlastimil Babka wrote: > On 08/26/2015 04:45 PM, Mel Gorman wrote: > >On Tue, Aug 25, 2015 at 05:37:59PM +0200, Vlastimil Babka wrote: > >>>@@ -2158,7 +2158,7 @@ static bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order) > >>> return false; > >>> if (fail_page_alloc.ignore_gfp_highmem && (gfp_mask & __GFP_HIGHMEM)) > >>> return false; > >>>- if (fail_page_alloc.ignore_gfp_wait && (gfp_mask & __GFP_WAIT)) > >>>+ if (fail_page_alloc.ignore_gfp_wait && (gfp_mask & (__GFP_ATOMIC|__GFP_DIRECT_RECLAIM))) > >>> return false; > >>> > >>> return should_fail(&fail_page_alloc.attr, 1 << order); > >> > >>IIUC ignore_gfp_wait tells it to assume that reclaimers will eventually > >>succeed (for some reason?), so they shouldn't fail. Probably to focus the > >>testing on atomic allocations. But your change makes atomic allocation never > >>fail, so that goes against the knob IMHO? > >> > > > >Fair point, I'll remove the __GFP_ATOMIC check. I felt this was a sensible > >but then again deliberately failing allocations makes my brain twitch a > >bit. In retrospect, someone who cared should add a ignore_gfp_atomic knob. > > Thanks. > > >>>@@ -2660,7 +2660,7 @@ void warn_alloc_failed(gfp_t gfp_mask, int order, const char *fmt, ...) > >>> if (test_thread_flag(TIF_MEMDIE) || > >>> (current->flags & (PF_MEMALLOC | PF_EXITING))) > >>> filter &= ~SHOW_MEM_FILTER_NODES; > >>>- if (in_interrupt() || !(gfp_mask & __GFP_WAIT)) > >>>+ if (in_interrupt() || !(gfp_mask & __GFP_WAIT) || (gfp_mask & __GFP_ATOMIC)) > >>> filter &= ~SHOW_MEM_FILTER_NODES; > >>> > >>> if (fmt) { > >> > >>This caught me previously and I convinced myself that it's OK, but now I'm > >>not anymore. IIUC this is to not filter nodes by mems_allowed during > >>printing, if the allocation itself wasn't limited? In that case it should > >>probably only look at __GFP_ATOMIC after this patch? As that's the only > >>thing that determines ALLOC_CPUSET. > >>I don't know where in_interrupt() comes from, but it was probably considered > >>in the past, as can be seen in zlc_setup()? > >> > > > >I assumed the in_interrupt() thing was simply because cpusets were the > >primary means of limiting allocations of interest to the author at the > >time. > > IIUC this hunk is unrelated to the previous one - not about limiting > allocations, but printing allocation warnings. Which includes the state of > nodes where the allocation was allowed to try. And ~SHOW_MEM_FILTER_NODES > means it was allowed everywhere, so the printing won't filter by > mems_allowed. > > >I guess now that I think about it more that a more sensible check would > >be against __GFP_DIRECT_RECLAIM because that covers the interesting > >cases. > > I think the most robust check would be to rely on what was already prepared > by gfp_to_alloc_flags(), instead of repeating it here. So add alloc_flags > parameter to warn_alloc_failed(), and drop the filter when > - ALLOC_CPUSET is not set, as that disables the cpuset checks > - ALLOC_NO_WATERMARKS is set, as that allows calling > __alloc_pages_high_priority() attempt which ignores cpusets > warn_alloc_failed is used outside of page_alloc.c in a context that does not have alloc_flags. It could be extended to take an extra parameter that is ALLOC_CPUSET for the other callers or else split it into __warn_alloc_failed (takes alloc_flags parameter) and warn_alloc_failed (calls __warn_alloc_failed with ALLOC_CPUSET) but is it really worth it? -- Mel Gorman SUSE Labs