From mboxrd@z Thu Jan 1 00:00:00 1970 From: Minchan Kim Subject: Re: [PATCH v3 01/17] mm: support madvise(MADV_FREE) Date: Fri, 13 Nov 2015 15:38:02 +0900 Message-ID: <20151113063802.GF5235@bbox> References: <1447302793-5376-1-git-send-email-minchan@kernel.org> <1447302793-5376-2-git-send-email-minchan@kernel.org> <564421DA.9060809@gmail.com> <20151113061511.GB5235@bbox> <56458056.8020105@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Return-path: In-Reply-To: <56458056.8020105-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Content-Disposition: inline Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Daniel Micay Cc: Andy Lutomirski , Andrew Morton , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org" , Michael Kerrisk , Linux API , Hugh Dickins , Johannes Weiner , Rik van Riel , Mel Gorman , KOSAKI Motohiro , Jason Evans , "Kirill A. Shutemov" , Shaohua Li , Michal Hocko , yalin wang List-Id: linux-api@vger.kernel.org On Fri, Nov 13, 2015 at 01:16:54AM -0500, Daniel Micay wrote: > On 13/11/15 01:15 AM, Minchan Kim wrote: > > On Thu, Nov 12, 2015 at 12:21:30AM -0500, Daniel Micay wrote: > >>> I also think that the kernel should commit to either zeroing the page > >>> or leaving it unchanged in response to MADV_FREE (even if the decision > >>> of which to do is made later on). I think that your patch series does > >>> this, but only after a few of the patches are applied (the swap entry > >>> freeing), and I think that it should be a real guaranteed part of the > >>> semantics and maybe have a test case. > >> > >> This would be a good thing to test because it would be required to add > >> MADV_FREE_UNDO down the road. It would mean the same semantics as the > >> MEM_RESET and MEM_RESET_UNDO features on Windows, and there's probably > >> value in that for the sake of migrating existing software too. > > > > So, do you mean that we could implement MADV_FREE_UNDO with "read" > > opearation("just access bit marking) easily in future? > > > > If so, it would be good reason to change MADV_FREE from dirty bit to > > access bit. Okay, I will look at that. > > I just meant testing that the data is either zero or the old data if > it's read before it's written to. Not having it stay around once there > is a read. Not sure if that's what Andy meant. Either zero of old data is gauranteed. Now: MADV_FREE(range) A = read from the range ... ... B = read from the range A and B could have different value. But value should be old or zero. But Andy want more strict ABI so he suggested access bit instead of dirty bit. MADV_FREE(range) A = read from the range ... ... B = read from the range A and B cannot have different value. And now I am thinking if we use access bit, we could implment MADV_FREE_UNDO easily when we need it. Maybe, that's what you want. Right?