From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751018AbbJ1EEH (ORCPT ); Wed, 28 Oct 2015 00:04:07 -0400 Received: from mail-pa0-f49.google.com ([209.85.220.49]:35350 "EHLO mail-pa0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750737AbbJ1EEG convert rfc822-to-8bit (ORCPT ); Wed, 28 Oct 2015 00:04:06 -0400 Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 9.0 \(3094\)) Subject: Re: [PATCH 4/5] mm: simplify reclaim path for MADV_FREE From: yalin wang In-Reply-To: Date: Wed, 28 Oct 2015 12:03:57 +0800 Cc: Hugh Dickins , Andrew Morton , "open list:MEMORY MANAGEMENT" , lkml , Rik van Riel , Mel Gorman , Michal Hocko , Johannes Weiner , "Kirill A. Shutemov" , Vlastimil Babka Content-Transfer-Encoding: 8BIT Message-Id: <9482C2F5-0215-44C0-9247-EDDFC7403BD9@gmail.com> References: <1445236307-895-1-git-send-email-minchan@kernel.org> <1445236307-895-5-git-send-email-minchan@kernel.org> <20151027070903.GD26803@bbox> <32537EDE-3EE6-4C44-B820-5BCAF7A5D535@gmail.com> <20151027081059.GE26803@bbox> To: Minchan Kim X-Mailer: Apple Mail (2.3094) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Oct 27, 2015, at 16:52, yalin wang wrote: > > >> On Oct 27, 2015, at 16:10, Minchan Kim wrote: >> >> On Tue, Oct 27, 2015 at 03:39:16PM +0800, yalin wang wrote: >>> >>>> On Oct 27, 2015, at 15:09, Minchan Kim wrote: >>>> >>>> Hello Yalin, >>>> >>>> Sorry for missing you in Cc list. >>>> IIRC, mails to send your previous mail address(Yalin.Wang@sonymobile.com) >>>> were returned. >>>> >>>> You added comment bottom line so I'm not sure what PageDirty you meant. >>>> >>>>> it is wrong here if you only check PageDirty() to decide if the page is freezable or not . >>>>> The Anon page are shared by multiple process, _mapcount > 1 , >>>>> so you must check all pt_dirty bit during page_referenced() function, >>>>> see this mail thread: >>>>> http://ns1.ske-art.com/lists/kernel/msg1934021.html >>>> >>>> If one of pte among process sharing the page was dirty, the dirtiness should >>>> be propagated from pte to PG_dirty by try_to_unmap_one. >>>> IOW, if the page doesn't have PG_dirty flag, it means all of process did >>>> MADV_FREE. >>>> >>>> Am I missing something from you question? >>>> If so, could you show exact scenario I am missing? >>>> >>>> Thanks for the interest. >>> oh, yeah , that is right , i miss that , pte_dirty will propagate to PG_dirty , >>> so that is correct . >>> Generic to say this patch move set_page_dirty() from add_to_swap() to >>> try_to_unmap(), i think can change a little about this patch: >>> >>> @@ -1476,6 +1446,8 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, >>> ret = SWAP_FAIL; >>> goto out_unmap; >>> } >>> + if (!PageDirty(page)) >>> + SetPageDirty(page); >>> if (list_empty(&mm->mmlist)) { >>> spin_lock(&mmlist_lock); >>> if (list_empty(&mm->mmlist)) >>> >>> i think this 2 lines can be removed , >>> since pte_dirty have propagated to set_page_dirty() , we don’t need this line here , >>> otherwise you will always dirty a AnonPage, even it is clean, >>> then we will page out this clean page to swap partition one more , this is not needed. >>> am i understanding correctly ? >> >> Your understanding is correct. >> I will fix it in next spin. >> >>> >>> By the way, please change my mail address to yalin.wang2010@gmail.com in CC list . >>> Thanks a lot. :) >> >> Thanks for the review! > > i have a look at the old mail list , i recall the scenario that multiple processes share a AnonPage > special case : > > for example Process A have a AnonPage map like this: > ! pte_dirty() && PageDirty()==1 (this is possible after read fault happened on swap entry, and try_to_free_swap() succeed.) > Process A do a fork() , New process is called B . > Then A syscall(MADV_FREE) on the page . > At this time, page table like this: > > A ! pte_dirty() && PageDirty() == 0 && PageSwapCache() == 0 > > B ! pte_dirty() && PageDirty() == 0 && PageSwapCache() == 0 > > This means this page is freeable , and can be freed during page reclaim. > This is not fair for Process B . Since B don’t call syscall(MADV_FREE) , > its page should not be discard . Will cause some strange behaviour if happened . > > This is discussed by > http://www.serverphorums.com/read.php?12,1220840 > but i don’t know why the patch is not merged . > > Thanks oh, i have see 0b502297d1cc26e09b98955b4efa728be1c48921 this commit merged , then this problem should be fixed by this method. ignore this mail. :) Thanks a lot .