From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422985AbbEONl0 (ORCPT ); Fri, 15 May 2015 09:41:26 -0400 Received: from mta-out1.inet.fi ([62.71.2.227]:42151 "EHLO jenni2.inet.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1422800AbbEONlY (ORCPT ); Fri, 15 May 2015 09:41:24 -0400 Date: Fri, 15 May 2015 16:41:03 +0300 From: "Kirill A. Shutemov" 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 Subject: Re: [PATCHv5 07/28] thp, mlock: do not allow huge pages in mlocked area Message-ID: <20150515134103.GC6625@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5555ED0A.5010702@suse.cz> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? -- Kirill A. Shutemov From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f170.google.com (mail-wi0-f170.google.com [209.85.212.170]) by kanga.kvack.org (Postfix) with ESMTP id 894FA6B0032 for ; Fri, 15 May 2015 09:41:14 -0400 (EDT) Received: by wizk4 with SMTP id k4so287569904wiz.1 for ; Fri, 15 May 2015 06:41:14 -0700 (PDT) Received: from jenni2.inet.fi (mta-out1.inet.fi. [62.71.2.227]) by mx.google.com with ESMTP id hu2si3810410wib.17.2015.05.15.06.41.12 for ; Fri, 15 May 2015 06:41:13 -0700 (PDT) Date: Fri, 15 May 2015 16:41:03 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCHv5 07/28] thp, mlock: do not allow huge pages in mlocked area Message-ID: <20150515134103.GC6625@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5555ED0A.5010702@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 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? -- 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