From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f177.google.com (mail-wi0-f177.google.com [209.85.212.177]) by kanga.kvack.org (Postfix) with ESMTP id F40316B0106 for ; Wed, 20 May 2015 08:11:03 -0400 (EDT) Received: by wizk4 with SMTP id k4so152745836wiz.1 for ; Wed, 20 May 2015 05:11:03 -0700 (PDT) Received: from jenni1.inet.fi (mta-out1.inet.fi. [62.71.2.203]) by mx.google.com with ESMTP id g4si19350677wjs.66.2015.05.20.05.11.01 for ; Wed, 20 May 2015 05:11:02 -0700 (PDT) Date: Wed, 20 May 2015 15:10:48 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCHv5 07/28] thp, mlock: do not allow huge pages in mlocked area Message-ID: <20150520121048.GA13921@node.dhcp.inet.fi> References: <1429823043-157133-1-git-send-email-kirill.shutemov@linux.intel.com> <1429823043-157133-8-git-send-email-kirill.shutemov@linux.intel.com> <5555ED0A.5010702@suse.cz> <20150515134103.GC6625@node.dhcp.inet.fi> <555B4AA5.7000504@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <555B4AA5.7000504@suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka Cc: "Kirill A. Shutemov" , Andrew Morton , Andrea Arcangeli , Hugh Dickins , Dave Hansen , Mel Gorman , Rik van Riel , Christoph Lameter , Naoya Horiguchi , Steve Capper , "Aneesh Kumar K.V" , Johannes Weiner , Michal Hocko , Jerome Marchand , Sasha Levin , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Tue, May 19, 2015 at 04:37:25PM +0200, Vlastimil Babka wrote: > On 05/15/2015 03:41 PM, Kirill A. Shutemov wrote: > >On Fri, May 15, 2015 at 02:56:42PM +0200, Vlastimil Babka wrote: > >>On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote: > >>>With new refcounting THP can belong to several VMAs. This makes tricky > >>>to track THP pages, when they partially mlocked. It can lead to leaking > >>>mlocked pages to non-VM_LOCKED vmas and other problems. > >>>With this patch we will split all pages on mlock and avoid > >>>fault-in/collapse new THP in VM_LOCKED vmas. > >>> > >>>I've tried alternative approach: do not mark THP pages mlocked and keep > >>>them on normal LRUs. This way vmscan could try to split huge pages on > >>>memory pressure and free up subpages which doesn't belong to VM_LOCKED > >>>vmas. But this is user-visible change: we screw up Mlocked accouting > >>>reported in meminfo, so I had to leave this approach aside. > >>> > >>>We can bring something better later, but this should be good enough for > >>>now. > >> > >>I can imagine people won't be happy about losing benefits of THP's when they > >>mlock(). > >>How difficult would it be to support mlocked THP pages without splitting > >>until something actually tries to do a partial (un)mapping, and only then do > >>the split? That will support the most common case, no? > > > >Yes, it will. > > > >But what will we do if we fail to split huge page on munmap()? Fail > >munmap() with -EBUSY? > > We could just unmlock the whole THP page and if we could make the deferred > split done ASAP, and not waiting for memory pressure, the window with > NR_MLOCK being undercounted would be minimized. Since the RLIMIT_MEMLOCK is > tracked independently from NR_MLOCK, there should be no danger wrt breaching > the limit due to undercounting here? I'm not sure what "ASAP" should mean here and how to implement it. I would really prefer to address mlock separately. The patchset is already huge enough. :-/ -- Kirill A. Shutemov -- 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