From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx181.postini.com [74.125.245.181]) by kanga.kvack.org (Postfix) with SMTP id DDA626B0005 for ; Sun, 20 Jan 2013 20:52:24 -0500 (EST) Date: Mon, 21 Jan 2013 10:52:22 +0900 From: Minchan Kim Subject: Re: [PATCH 1/2] mm: prevent to add a page to swap if may_writepage is unset Message-ID: <20130121015222.GA3666@blaptop> References: <1357712474-27595-1-git-send-email-minchan@kernel.org> <1357712474-27595-2-git-send-email-minchan@kernel.org> <20130116134155.18092f1a.akpm@linux-foundation.org> <20130117005314.GB18669@blaptop> <20130117142238.e32c46d5.akpm@linux-foundation.org> <20130117233641.GA31368@blaptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130117233641.GA31368@blaptop> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dan Magenheimer , Sonny Rao , Bryan Freed , Hugh Dickins , Rik van Riel , Johannes Weiner Hi, On Fri, Jan 18, 2013 at 08:36:42AM +0900, Minchan Kim wrote: > On Thu, Jan 17, 2013 at 02:22:38PM -0800, Andrew Morton wrote: > > On Thu, 17 Jan 2013 09:53:14 +0900 > > Minchan Kim wrote: > > > > > Recently, Luigi reported there are lots of free swap space when > > > OOM happens. It's easily reproduced on zram-over-swap, where > > > many instance of memory hogs are running and laptop_mode is enabled. > > > He said there was no problem when he disabled laptop_mode. > > > > > > The problem when I investigate problem is following as. > > > > > > Assumption for easy explanation: There are no page cache page in system > > > because they all are already reclaimed. > > > > > > 1. try_to_free_pages disable may_writepage when laptop_mode is enabled. > > > 2. shrink_inactive_list isolates victim pages from inactive anon lru list. > > > 3. shrink_page_list adds them to swapcache via add_to_swap but it doesn't > > > pageout because sc->may_writepage is 0 so the page is rotated back into > > > inactive anon lru list. The add_to_swap made the page Dirty by SetPageDirty > > > 4. 3 couldn't reclaim any pages so do_try_to_free_pages increase priority and > > > retry reclaim with higher priority. > > > 5. shrink_inactlive_list try to isolate victim pages from inactive anon lru list > > > but got failed because it try to isolate pages with ISOLATE_CLEAN mode but > > > inactive anon lru list is full of dirty pages by 3 so it just returns > > > without any reclaim progress. > > > 6. do_try_to_free_pages doesn't set may_write due to zero total_scanned. > > > > s/may_write/may_writepage/ > > Thanks! > > > > > > Because sc->nr_scanned is increased by shrink_page_list but we don't call > > > shrink_page_list in 5 due to short of isolated pages. > > > > This is the bug, is it not? > > > > In laptop mode, we still need to write out dirty swapcache at some > > point. An appropriate time to do this is when the scanning priority is > > Yes and when to some point is really important. Now, the point for that is > depends on on the number of scanned pages by shrink_page_list. It means we > must isolate victim pages from inactive LRU list and call shrink_page_list > to increase sc->nr_scanned but unfortunately, we have various filters to > decrease CPU consumption and LRU churning when VM try to isolate victim pages > so it could prevent isolating victim pages from LRU list. > > > getting high. But it seems that this ISOLATE_CLEAN->total_scanned > > Yes. I absolutely agree on that some point should depend on priority, NOT > the number of scanned pages. And I already said to you about that. > https://lkml.org/lkml/2013/1/10/643 > > We used to use such heuristic in several places in VM, ie DEF_PRIORITY - 2 > But why I hesitate with the patch is that I think this patch should go to > stable tree so the patch should be really small and have no side effect so > I don't wanted to change laptop_mode behavior heavily caused by changing > condition for may_writepage trigger point. > > > interaction is preventing that. > > > > (An enhancement to laptop mode would be to opportunistically write out > > dirty swapcache in or around laptop_mode_timer_fn()). > > It could but it should be another patch and VM shouldn't rely on ONLY > laptop_mode_timer_fn, IMHO. VM should have own rule to reclaim pages > regardless of laptop_mode's help to prevent OOM kill. > > > > > > Above loop is continued until OOM happens. > > > The problem didn't happen before [1] was merged because old logic's isolatation > > > in shrink_inactive_list was successful and tried to call shrink_page_list > > > to pageout them but it still ends up failed to page out by may_writepage. > > > But important point is that sc->nr_scanned was increased althoug we couldn't > > > swap out them so do_try_to_free_pages could set may_writepages. > > > So this patch need to go stable tree althoug it's a band-aid. > > > Then, for latest linus tree, we should fix laptop_mode's fundamental > > > problem. > > > > Well. Perhaps we can do that now. > > Okay. If you don't object my suggestion, I will send patches next week. > Thanks for the review, Andrew! Andrew, If nobody objects, I would like to drop [1] and add ths patch instead of [1]. Luigi, below patch passed my test. If anybody doesn't object, could you test this patch? Thanks! [1] mm: prevent addition of pages to swap if may_writepage is unset -------------- &< --------------------