From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx109.postini.com [74.125.245.109]) by kanga.kvack.org (Postfix) with SMTP id B13236B006C for ; Sun, 14 Jul 2013 20:03:36 -0400 (EDT) Received: by mail-pa0-f50.google.com with SMTP id fb1so10683963pad.9 for ; Sun, 14 Jul 2013 17:03:36 -0700 (PDT) Date: Mon, 15 Jul 2013 08:22:16 +0800 From: Zheng Liu Subject: Re: [RFC][PATCH] mm: madvise: MADV_POPULATE for quick pre-faulting Message-ID: <20130715002216.GA6403@gmail.com> 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> <51E2173A.8080003@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51E2173A.8080003@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Sam Ben Cc: Dave Hansen , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Sun, Jul 14, 2013 at 11:12:58AM +0800, Sam Ben wrote: > 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? Yes, in our product system most applications do like this. Regards, - Zheng -- 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