From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752497AbbKYK7X (ORCPT ); Wed, 25 Nov 2015 05:59:23 -0500 Received: from mail-pa0-f44.google.com ([209.85.220.44]:33036 "EHLO mail-pa0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752338AbbKYK7W (ORCPT ); Wed, 25 Nov 2015 05:59:22 -0500 Date: Wed, 25 Nov 2015 02:59:19 -0800 (PST) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Michal Hocko cc: Andrew Morton , Mel Gorman , Johannes Weiner , linux-mm@kvack.org, LKML , Michal Hocko Subject: Re: [PATCH 2/2] mm: warn about ALLOC_NO_WATERMARKS request failures In-Reply-To: <1448448054-804-3-git-send-email-mhocko@kernel.org> Message-ID: References: <1448448054-804-1-git-send-email-mhocko@kernel.org> <1448448054-804-3-git-send-email-mhocko@kernel.org> 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 On Wed, 25 Nov 2015, Michal Hocko wrote: > From: Michal Hocko > > ALLOC_NO_WATERMARKS requests can dive into memory reserves without any > restriction. They are used only in the case of emergency to allow > forward memory reclaim progress assuming the caller should return the > memory in a short time (e.g. {__GFP,PF}_MEMALLOC requests or OOM victim > on the way to exit or __GFP_NOFAIL requests hitting OOM). There is no > guarantee such request succeed because memory reserves might get > depleted as well. This might be either a result of a bug where memory > reserves are abused or a result of a too optimistic configuration of > memory reserves. > > This patch makes sure that the administrator gets a warning when these > requests fail with a hint that min_free_kbytes might be used to increase > the amount of memory reserves. The warning might also help us check > whether the issue is caused by a buggy user or the configuration. To > prevent from flooding the logs the warning is on off but we allow it to > trigger again after min_free_kbytes was updated. Something really bad is > clearly going on if the warning hits even after multiple updates of > min_free_kbytes. > > Signed-off-by: Michal Hocko > --- > mm/page_alloc.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 70db11c27046..6a05d771cb08 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -240,6 +240,8 @@ compound_page_dtor * const compound_page_dtors[] = { > #endif > }; > > +/* warn about depleted watermarks */ > +static bool warn_alloc_no_wmarks; > int min_free_kbytes = 1024; > int user_min_free_kbytes = -1; > > @@ -2642,6 +2644,13 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags, > if (zonelist_rescan) > goto zonelist_scan; > > + /* WARN only once unless min_free_kbytes is updated */ > + if (warn_alloc_no_wmarks && (alloc_flags & ALLOC_NO_WATERMARKS)) { > + warn_alloc_no_wmarks = 0; > + WARN(1, "Memory reserves are depleted for order:%d, mode:0x%x." > + " You might consider increasing min_free_kbytes\n", > + order, gfp_mask); > + } > return NULL; > } > Doesn't this warn for high-order allocations prior to the first call to direct compaction whereas min_free_kbytes may be irrelevant? Providing the order is good, but there's no indication when min_free_kbytes may be helpful from this warning. WARN() isn't even going to show the state of memory.