From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-la0-f53.google.com (mail-la0-f53.google.com [209.85.215.53]) by kanga.kvack.org (Postfix) with ESMTP id CECE96B0038 for ; Tue, 3 Feb 2015 05:48:07 -0500 (EST) Received: by mail-la0-f53.google.com with SMTP id gq15so50211354lab.12 for ; Tue, 03 Feb 2015 02:48:07 -0800 (PST) Received: from jenni2.inet.fi (mta-out1.inet.fi. [62.71.2.227]) by mx.google.com with ESMTP id w8si6934201lbb.25.2015.02.03.02.48.05 for ; Tue, 03 Feb 2015 02:48:05 -0800 (PST) Date: Tue, 3 Feb 2015 12:47:56 +0200 From: "Kirill A. Shutemov" Subject: Re: [RFC PATCH] mm: madvise: Ignore repeated MADV_DONTNEED hints Message-ID: <20150203104756.GB14259@node.dhcp.inet.fi> References: <20150202165525.GM2395@suse.de> <54CFF8AC.6010102@intel.com> <20150203094718.GO2395@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150203094718.GO2395@suse.de> Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Dave Hansen , linux-mm@kvack.org, Minchan Kim , Vlastimil Babka , Andrew Morton , linux-kernel@vger.kernel.org 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 -- 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