Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753600AbbKWV0x (ORCPT ); Mon, 23 Nov 2015 16:26:53 -0500 Received: from mail-pa0-f44.google.com ([209.85.220.44]:36557 "EHLO mail-pa0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751270AbbKWV0w (ORCPT ); Mon, 23 Nov 2015 16:26:52 -0500 Date: Mon, 23 Nov 2015 13:26:49 -0800 (PST) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Michal Hocko cc: Vlastimil Babka , Andrew Morton , Johannes Weiner , Andrea Arcangeli , Mel Gorman , linux-mm@kvack.org, LKML Subject: Re: [PATCH] mm, oom: Give __GFP_NOFAIL allocations access to memory reserves In-Reply-To: <20151123101345.GF21050@dhcp22.suse.cz> Message-ID: References: <1447249697-13380-1-git-send-email-mhocko@kernel.org> <5651BB43.8030102@suse.cz> <20151123092925.GB21050@dhcp22.suse.cz> <5652DFCE.3010201@suse.cz> <20151123101345.GF21050@dhcp22.suse.cz> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2566 Lines: 55 On Mon, 23 Nov 2015, Michal Hocko wrote: > > >>>diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > >>>index 8034909faad2..d30bce9d7ac8 100644 > > >>>--- a/mm/page_alloc.c > > >>>+++ b/mm/page_alloc.c > > >>>@@ -2766,8 +2766,16 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order, > > >>> goto out; > > >>> } > > >>> /* Exhausted what can be done so it's blamo time */ > > >>>- if (out_of_memory(&oc) || WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL)) > > >>>+ if (out_of_memory(&oc) || WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL)) { > > >>> *did_some_progress = 1; > > >>>+ > > >>>+ if (gfp_mask & __GFP_NOFAIL) { > > >>>+ page = get_page_from_freelist(gfp_mask, order, > > >>>+ ALLOC_NO_WATERMARKS|ALLOC_CPUSET, ac); > > >>>+ WARN_ONCE(!page, "Unable to fullfil gfp_nofail allocation." > > >>>+ " Consider increasing min_free_kbytes.\n"); > > >> > > >>It seems redundant to me to keep the WARN_ON_ONCE also above in the if () part? > > > > > >They are warning about two different things. The first one catches a > > >buggy code which uses __GFP_NOFAIL from oom disabled context while the > > > > Ah, I see, I misinterpreted what the return values of out_of_memory() mean. > > But now that I look at its code, it seems to only return false when > > oom_killer_disabled is set to true. Which is a global thing and nothing to > > do with the context of the __GFP_NOFAIL allocation? > > I am not sure I follow you here. The point of the warning is to warn > when the oom killer is disbaled (out_of_memory returns false) _and_ the > request is __GFP_NOFAIL because we simply cannot guarantee any forward > progress and just a use of the allocation flag is not supproted. > I don't think the WARN_ONCE() above is helpful for a few reasons: - it suggests that min_free_kbytes is the best way to work around such issues and gives kernel developers a free pass to just say "raise min_free_kbytes" rather than reducing their reliance on __GFP_NOFAIL, - raising min_free_kbytes is not immediately actionable without memory freeing to fix any oom issue, and - it relies on the earlier warning to dump the state of memory and doesn't add any significant information to help understand how seperate occurrences are similar or different. I think the WARN_ONCE() should just be removed. -- 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/