From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx114.postini.com [74.125.245.114]) by kanga.kvack.org (Postfix) with SMTP id 216EF6B006C for ; Fri, 21 Dec 2012 16:51:48 -0500 (EST) Received: by mail-we0-f180.google.com with SMTP id t57so2399721wey.11 for ; Fri, 21 Dec 2012 13:51:46 -0800 (PST) MIME-Version: 1.0 In-Reply-To: References: <1353624594-1118-1-git-send-email-mingo@kernel.org> <1353624594-1118-19-git-send-email-mingo@kernel.org> <20121221134740.GC13367@suse.de> From: Linus Torvalds Date: Fri, 21 Dec 2012 13:51:26 -0800 Message-ID: Subject: Re: [patch] mm, mempolicy: Introduce spinlock to read shared policy tree Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Mel Gorman , David Rientjes , Ingo Molnar , Linux Kernel Mailing List , linux-mm , Peter Zijlstra , Paul Turner , Lee Schermerhorn , Christoph Lameter , Rik van Riel , Andrew Morton , Andrea Arcangeli , Thomas Gleixner , Johannes Weiner , Sasha Levin , KOSAKI Motohiro On Fri, Dec 21, 2012 at 10:21 AM, Hugh Dickins wrote: > On Fri, 21 Dec 2012, Linus Torvalds wrote: >> >> compared to the diseased abortion you just posted. > > I'm picking up a vibe that you don't entirely like Mel's approach. Good job. I was a bit nervous that I was being too subtle. > I don't understand David's and Mel's remarks about the "shared pages" > check making Sasha's warning unlikely: page_mapcount has nothing to do > with whether a page belongs to shm/shmem/tmpfs, and it's easy enough > to reproduce Sasha's warning on the current git tree. "mount -o > remount,mpol=local /tmp" or something like that is useful in testing. I think that Mel and David may talk about the mutex actually blocking (not just the debug message possibly triggering). > I wish wish wish I had time to spend on this today, but I don't. > And I've not looked to see (let alone tested) whether it's easy > to revert Mel's mutex then add in Kosaki's patch (which I didn't > look at so have no opinion on). I don't actually have Kosaki's patch either, just the description of it. We've done that kind of "preallocate before taking the lock" before, though. > Shall we go for Peter/David's mutex+spinlock for rc1 - I assume > they both tested that - with a promise to do better in rc2? Well, if the plan is to fix it for rc2, then there is no point in putting a workaround in now, since actually hitting the problem (as opposed to seeing the warning) is presumably much harder. Linus -- 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