From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx165.postini.com [74.125.245.165]) by kanga.kvack.org (Postfix) with SMTP id 740B26B0032 for ; Mon, 1 Jul 2013 22:19:14 -0400 (EDT) Received: by mail-pb0-f52.google.com with SMTP id xa12so5497464pbc.11 for ; Mon, 01 Jul 2013 19:19:13 -0700 (PDT) Date: Tue, 2 Jul 2013 10:37:48 +0800 From: Zheng Liu Subject: Re: [RFC][PATCH] mm: madvise: MADV_POPULATE for quick pre-faulting Message-ID: <20130702023748.GA10366@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51D1AB6E.9030905@sr71.net> Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org 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. 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