Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752306Ab3GNDNH (ORCPT ); Sat, 13 Jul 2013 23:13:07 -0400 Received: from mail-ie0-f182.google.com ([209.85.223.182]:33771 "EHLO mail-ie0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752208Ab3GNDNF (ORCPT ); Sat, 13 Jul 2013 23:13:05 -0400 Message-ID: <51E2173A.8080003@gmail.com> Date: Sun, 14 Jul 2013 11:12:58 +0800 From: Sam Ben User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130329 Thunderbird/17.0.5 MIME-Version: 1.0 To: Dave Hansen , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC][PATCH] mm: madvise: MADV_POPULATE for quick pre-faulting References: <20130627231605.8F9F12E6@viggo.jf.intel.com> <20130628054757.GA10429@gmail.com> <51CDB056.5090308@sr71.net> <51CE4451.4060708@gmail.com> <51D1AB6E.9030905@sr71.net> <20130702023748.GA10366@gmail.com> In-Reply-To: <20130702023748.GA10366@gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2238 Lines: 49 On 07/02/2013 10:37 AM, Zheng Liu wrote: > On Mon, Jul 01, 2013 at 09:16:46AM -0700, Dave Hansen wrote: >> On 06/28/2013 07:20 PM, Zheng Liu wrote: >>>>> IOW, a process needing to do a bunch of MAP_POPULATEs isn't >>>>> parallelizable, but one using this mechanism would be. >>> I look at the code, and it seems that we will handle MAP_POPULATE flag >>> after we release mmap_sem locking in vm_mmap_pgoff(): >>> >>> down_write(&mm->mmap_sem); >>> ret = do_mmap_pgoff(file, addr, len, prot, flag, pgoff, >>> &populate); >>> up_write(&mm->mmap_sem); >>> if (populate) >>> mm_populate(ret, populate); >>> >>> Am I missing something? >> I went and did my same test using mmap(MAP_POPULATE)/munmap() pair >> versus using MADV_POPULATE in 160 threads in parallel. >> >> MADV_POPULATE was about 10x faster in the threaded configuration. >> >> With MADV_POPULATE, the biggest cost is shipping the mmap_sem cacheline >> around so that we can write the reader count update in to it. With >> mmap(), there is a lot of _contention_ on that lock which is much, much >> more expensive than simply bouncing a cacheline around. > Thanks for your explanation. > > FWIW, it would be great if we can let MAP_POPULATE flag support shared > mappings because in our product system there has a lot of applications > that uses mmap(2) and then pre-faults this mapping. Currently these > applications need to pre-fault the mapping manually. How do you pre-fault the mapping manually in your product system? By walking through the file touching each page? > > Regards, > - Zheng > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/