From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-la0-f41.google.com (mail-la0-f41.google.com [209.85.215.41]) by kanga.kvack.org (Postfix) with ESMTP id 6FA796B006E for ; Fri, 30 Jan 2015 08:30:54 -0500 (EST) Received: by mail-la0-f41.google.com with SMTP id gm9so23745712lab.0 for ; Fri, 30 Jan 2015 05:30:53 -0800 (PST) Received: from forward-corp1g.mail.yandex.net (forward-corp1g.mail.yandex.net. [2a02:6b8:0:1402::10]) by mx.google.com with ESMTPS id wn10si10099718lac.76.2015.01.30.05.30.52 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 30 Jan 2015 05:30:52 -0800 (PST) Message-ID: <54CB8789.9040206@yandex-team.ru> Date: Fri, 30 Jan 2015 16:30:49 +0300 From: Konstantin Khlebnikov MIME-Version: 1.0 Subject: Re: [PATCH] mm: don't account shared file pages in user_reserve_pages References: <1422532287-23601-1-git-send-email-klamm@yandex-team.ru> <20150129201147.GB9331@scruffy> In-Reply-To: <20150129201147.GB9331@scruffy> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Shewmaker , Roman Gushchin Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Rik van Riel On 29.01.2015 23:11, Andrew Shewmaker wrote: > On Thu, Jan 29, 2015 at 02:51:27PM +0300, Roman Gushchin wrote: >> Shared file pages are never accounted in memory overcommit code, >> so it isn't reasonable to count them in a code that limits the >> maximal size of a process in OVERCOMMIT_NONE mode. >> >> If a process has few large file mappings, the consequent attempts >> to allocate anonymous memory may unexpectedly fail with -ENOMEM, >> while there is free memory and overcommit limit if significantly >> larger than the committed amount (as displayed in /proc/meminfo). >> >> The problem is significantly smoothed by commit c9b1d0981fcc >> ("mm: limit growth of 3% hardcoded other user reserve"), >> which limits the impact of this check with 128Mb (tunable via sysctl), >> but it can still be a problem on small machines. >> >> Signed-off-by: Roman Gushchin >> Cc: Andrew Morton >> Cc: Andrew Shewmaker >> Cc: Rik van Riel >> Cc: Konstantin Khlebnikov >> --- >> mm/mmap.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/mmap.c b/mm/mmap.c >> index 7f684d5..151fadf 100644 >> --- a/mm/mmap.c >> +++ b/mm/mmap.c >> @@ -220,7 +220,7 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin) >> */ >> if (mm) { >> reserve = sysctl_user_reserve_kbytes >> (PAGE_SHIFT - 10); >> - allowed -= min(mm->total_vm / 32, reserve); >> + allowed -= min((mm->total_vm - mm->shared_vm) / 32, reserve); >> } >> >> if (percpu_counter_read_positive(&vm_committed_as) < allowed) >> -- >> 2.1.0 > > You're two patches conflict, don't they? Maybe you should resend > them as a patch series such that they can both be applied? I think arithmetic overflow is more important. Upper bound 128M for user reserve makes mis-accounting of shared memory mostly invisible. > > Does mm->shared_vm include memory that's mapped MAP_ANONYMOUS in > conjunction with MAP_SHARED? If so, then subtracting it could > overcommit the system OVERCOMMIT_NEVER mode. Yep. Moreover shared_vm also includes file mappings with MAP_PRIVATE. It works more likely as "maybe shared", upper bound for "file-rss" (MM_FILEPAGES). I think we need here total size of vmas where VM_ACCOUNT is set -- writable private mappings mapped without MAP_NORESERVE or something like that. But total_vm after limiting with 128Mb gives almost always the same or similar value. So, let's keep it as is. -- Konstantin > > -Andrew > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org