From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Piggin Subject: Re: [PATCH] mm: avoid dirtying shared mappings on mlock Date: Fri, 12 Oct 2007 04:14:10 +1000 References: <11854939641916-git-send-email-ssouhlal@FreeBSD.org> <200710120257.05960.nickpiggin@yahoo.com.au> <1192185439.27435.19.camel@twins> In-Reply-To: <1192185439.27435.19.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200710120414.11026.nickpiggin@yahoo.com.au> Sender: owner-linux-mm@kvack.org Return-Path: To: Peter Zijlstra Cc: Suleiman Souhlal , Andrew Morton , linux-kernel@vger.kernel.org, Suleiman Souhlal , linux-mm , hugh List-ID: On Friday 12 October 2007 20:37, Peter Zijlstra wrote: > On Fri, 2007-10-12 at 02:57 +1000, Nick Piggin wrote: > > On Friday 12 October 2007 19:03, Peter Zijlstra wrote: > > > Subject: mm: avoid dirtying shared mappings on mlock > > > > > > Suleiman noticed that shared mappings get dirtied when mlocked. > > > Avoid this by teaching make_pages_present about this case. > > > > > > Signed-off-by: Peter Zijlstra > > > Acked-by: Suleiman Souhlal > > > > Umm, I don't see the other piece of this thread, so I don't > > know what the actual problem was. > > > > But I would really rather not do this. If you do this, then you > > now can get random SIGBUSes when you write into the memory if it > > can't allocate blocks or ... (some other filesystem specific > > condition). > > I'm not getting this, make_pages_present() only has to ensure all the > pages are read from disk and in memory. How is this different from a > read-scan? I guess because we've mlocked a region that has PROT_WRITE access... but actually, I suppose mlock doesn't technically require that we can write to the memory, only that the page isn't swapped out. Still, it is nice to be able to have a reasonable guarantee of writability. > The pages will still be read-only due to dirty tracking, so the first > write will still do page_mkwrite(). Which can SIGBUS, no? -- 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