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Message-ID: <CAOMbAgLaFR+Et=F5+A7HPY16X-Y8VPm6mY_vE9XOJm8C-8OfPg@mail.gmail.com> Date: Thu, 3 Jan 2013 09:19:08 -0800 From: Sanjay Ghemawat <sanjay@...gle.com> To: Minchan Kim <minchan@...nel.org> Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Michael Kerrisk <mtk.manpages@...il.com>, Arun Sharma <asharma@...com>, Paul Turner <pjt@...gle.com>, David Rientjes <rientjes@...gle.com>, John Stultz <john.stultz@...aro.org>, Christoph Lameter <cl@...ux.com>, Android Kernel Team <kernel-team@...roid.com>, Robert Love <rlove@...gle.com>, Mel Gorman <mel@....ul.ie>, Hugh Dickins <hughd@...gle.com>, Dave Hansen <dave@...ux.vnet.ibm.com>, Rik van Riel <riel@...hat.com>, Dave Chinner <david@...morbit.com>, Neil Brown <neilb@...e.de>, Mike Hommey <mh@...ndium.org>, Taras Glek <tglek@...illa.com>, KOSAKI Motohiro <kosaki.motohiro@...il.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> Subject: Re: [RFC v5 0/8] Support volatile for anonymous range On Wed, Jan 2, 2013 at 8:27 PM, Minchan Kim <minchan@...nel.org> wrote: > This is still RFC because we need more input from user-space > people, more stress test, design discussion about interface/reclaim Speaking as one of the authors of tcmalloc, I don't see any particular need for this new system call for tcmalloc. We are fine using madvise(MADV_DONTNEED) and don't notice any significant performance issues caused by it. Background: we throttle how quickly we release memory back to the system (1-10MB/s), so we do not call madvise() very much, and we don't end up reusing madvise-ed away pages at a fast rate. My guess is that we won't see large enough application-level performance improvements to cause us to change tcmalloc to use this system call. > - What's different with madvise(DONTNEED)? > > System call semantic > > DONTNEED makes sure user always can see zero-fill pages after > he calls madvise while mvolatile can see old data or encounter > SIGBUS. Do you need a new system call for this? Why not just a new flag to madvise with weaker guarantees than zero-filling? All of the implementation changes you point out below could be triggered from that flag. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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