From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f181.google.com (mail-wi0-f181.google.com [209.85.212.181]) by kanga.kvack.org (Postfix) with ESMTP id 898D76B0036 for ; Tue, 3 Jun 2014 10:57:48 -0400 (EDT) Received: by mail-wi0-f181.google.com with SMTP id n15so6788088wiw.2 for ; Tue, 03 Jun 2014 07:57:48 -0700 (PDT) Received: from zene.cmpxchg.org (zene.cmpxchg.org. [2a01:238:4224:fa00:ca1f:9ef3:caee:a2bd]) by mx.google.com with ESMTPS id wf5si25504736wjb.92.2014.06.03.07.57.46 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Tue, 03 Jun 2014 07:57:47 -0700 (PDT) Date: Tue, 3 Jun 2014 10:57:10 -0400 From: Johannes Weiner Subject: Re: [PATCH 0/4] Volatile Ranges (v14 - madvise reborn edition!) Message-ID: <20140603145710.GQ2878@cmpxchg.org> References: <1398806483-19122-1-git-send-email-john.stultz@linaro.org> <536BBB08.3000503@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <536BBB08.3000503@linaro.org> Sender: owner-linux-mm@kvack.org List-ID: To: John Stultz Cc: LKML , Andrew Morton , Android Kernel Team , Robert Love , Mel Gorman , Hugh Dickins , Dave Hansen , Rik van Riel , Dmitry Adamushko , Neil Brown , Andrea Arcangeli , Mike Hommey , Taras Glek , Jan Kara , KOSAKI Motohiro , Michel Lespinasse , Minchan Kim , Keith Packard , "linux-mm@kvack.org" On Thu, May 08, 2014 at 10:12:40AM -0700, John Stultz wrote: > On 04/29/2014 02:21 PM, John Stultz wrote: > > Another few weeks and another volatile ranges patchset... > > > > After getting the sense that the a major objection to the earlier > > patches was the introduction of a new syscall (and its somewhat > > strange dual length/purged-bit return values), I spent some time > > trying to rework the vma manipulations so we can be we won't fail > > mid-way through changing volatility (basically making it atomic). > > I think I have it working, and thus, there is no longer the > > need for a new syscall, and we can go back to using madvise() > > to set and unset pages as volatile. > > Johannes: To get some feedback, maybe I'll needle you directly here a > bit. :) > > Does moving this interface to madvise help reduce your objections? I > feel like your cleaning-the-dirty-bit idea didn't work out, but I was > hoping that by reworking the vma manipulations to be atomic, we could > move to madvise and still avoid the new syscall that you seemed bothered > by. But I've not really heard much from you recently so I worry your > concerns on this were actually elsewhere, and I'm just churning the > patch needlessly. My objection was not the syscall. >>From a reclaim perspective, using the dirty state to denote whether a swap-backed page needs writeback before reclaim is quite natural and I much prefer Minchan's changes to the reclaim code over yours. >>From an interface point of view, I would prefer the simplicity of cleaning dirty bits to invalidate pages, and a default of zero-filling invalidated pages instead of sending SIGBUS. This also is quite natural when you think of anon/shmem mappings as cache pages on top of /dev/zero (see mmap_zero() and shmem_zero_setup()). And it translates well to tmpfs. At the same time, I acknowledge that there are usecases that want SIGBUS delivery for more than just convenience in order to implement userspace fault handling, and this is the only place where I see a real divergence in actual functionality from Minchan's code. That, however, truly is a separate virtual memory feature. Would it be possible for you to take MADV_FREE and MADV_REVIVE as a base and implement an madvise op that switches the no-page behavior of a VMA from zero-filling to SIGBUS delivery? -- 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