From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f41.google.com (mail-wg0-f41.google.com [74.125.82.41]) by kanga.kvack.org (Postfix) with ESMTP id B59736B0038 for ; Tue, 3 Feb 2015 06:21:30 -0500 (EST) Received: by mail-wg0-f41.google.com with SMTP id a1so43992543wgh.0 for ; Tue, 03 Feb 2015 03:21:30 -0800 (PST) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id gy6si6808867wib.19.2015.02.03.03.21.28 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 03 Feb 2015 03:21:29 -0800 (PST) Date: Tue, 3 Feb 2015 11:21:24 +0000 From: Mel Gorman Subject: Re: [RFC PATCH] mm: madvise: Ignore repeated MADV_DONTNEED hints Message-ID: <20150203112124.GS2395@suse.de> References: <20150202165525.GM2395@suse.de> <54CFF8AC.6010102@intel.com> <20150203094718.GO2395@suse.de> <20150203104756.GB14259@node.dhcp.inet.fi> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20150203104756.GB14259@node.dhcp.inet.fi> Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: Dave Hansen , linux-mm@kvack.org, Minchan Kim , Vlastimil Babka , Andrew Morton , linux-kernel@vger.kernel.org On Tue, Feb 03, 2015 at 12:47:56PM +0200, Kirill A. Shutemov wrote: > On Tue, Feb 03, 2015 at 09:47:18AM +0000, Mel Gorman wrote: > > On Mon, Feb 02, 2015 at 02:22:36PM -0800, Dave Hansen wrote: > > > On 02/02/2015 08:55 AM, Mel Gorman wrote: > > > > This patch identifies when a thread is frequently calling MADV_DONTNEED > > > > on the same region of memory and starts ignoring the hint. On an 8-core > > > > single-socket machine this was the impact on ebizzy using glibc 2.19. > > > > > > The manpage, at least, claims that we zero-fill after MADV_DONTNEED is > > > called: > > > > > > > It also claims that the kernel is free to ignore the advice. > > > > > > MADV_DONTNEED > > > > Do not expect access in the near future. (For the time being, the application is finished with the given range, so the kernel can free resources > > > > associated with it.) Subsequent accesses of pages in this range will succeed, but will result either in reloading of the memory contents from the > > > > underlying mapped file (see mmap(2)) or zero-fill-on-demand pages for mappings without an underlying file. > > > > > > So if we have anything depending on the behavior that it's _always_ > > > zero-filled after an MADV_DONTNEED, this will break it. > > > > True. I'd be surprised if any application depended on that > > IIUC, jemalloc depends on this[1]. > > [1] https://github.com/jemalloc/jemalloc/blob/dev/src/chunk_mmap.c#L117 > Hope they never back regions with hugetlb then or fall apart if the process called mlockall -- Mel Gorman SUSE Labs -- 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