From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f42.google.com (mail-pa0-f42.google.com [209.85.220.42]) by kanga.kvack.org (Postfix) with ESMTP id D1FBB82F64 for ; Wed, 28 Oct 2015 00:04:05 -0400 (EDT) Received: by padhk11 with SMTP id hk11so243409265pad.1 for ; Tue, 27 Oct 2015 21:04:05 -0700 (PDT) Received: from mail-pa0-x233.google.com (mail-pa0-x233.google.com. [2607:f8b0:400e:c03::233]) by mx.google.com with ESMTPS id fg5si67110081pbc.5.2015.10.27.21.04.05 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 27 Oct 2015 21:04:05 -0700 (PDT) Received: by pabla5 with SMTP id la5so50128230pab.0 for ; Tue, 27 Oct 2015 21:04:04 -0700 (PDT) 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 Content-Transfer-Encoding: quoted-printable 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> Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim Cc: Hugh Dickins , Andrew Morton , "open list:MEMORY MANAGEMENT" , lkml , Rik van Riel , Mel Gorman , Michal Hocko , Johannes Weiner , "Kirill A. Shutemov" , Vlastimil Babka > On Oct 27, 2015, at 16:52, yalin wang = wrote: >=20 >=20 >> On Oct 27, 2015, at 16:10, Minchan Kim wrote: >>=20 >> On Tue, Oct 27, 2015 at 03:39:16PM +0800, yalin wang wrote: >>>=20 >>>> On Oct 27, 2015, at 15:09, Minchan Kim wrote: >>>>=20 >>>> Hello Yalin, >>>>=20 >>>> Sorry for missing you in Cc list. >>>> IIRC, mails to send your previous mail = address(Yalin.Wang@sonymobile.com) >>>> were returned. >>>>=20 >>>> You added comment bottom line so I'm not sure what PageDirty you = meant. >>>>=20 >>>>> 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 >>>>=20 >>>> 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. >>>>=20 >>>> Am I missing something from you question? >>>> If so, could you show exact scenario I am missing? >>>>=20 >>>> 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=20 >>> try_to_unmap(), i think can change a little about this patch: >>>=20 >>> @@ -1476,6 +1446,8 @@ static int try_to_unmap_one(struct page *page, = struct vm_area_struct *vma, >>> ret =3D SWAP_FAIL; >>> goto out_unmap; >>> } >>> + if (!PageDirty(page)) >>> + SetPageDirty(page); >>> if (list_empty(&mm->mmlist)) { >>> spin_lock(&mmlist_lock); >>> if (list_empty(&mm->mmlist)) >>>=20 >>> i think this 2 lines can be removed , >>> since pte_dirty have propagated to set_page_dirty() , we don=E2=80=99= 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 ? >>=20 >> Your understanding is correct. >> I will fix it in next spin. >>=20 >>>=20 >>> By the way, please change my mail address to = yalin.wang2010@gmail.com in CC list . >>> Thanks a lot. :)=20 >>=20 >> Thanks for the review! >=20 > i have a look at the old mail list , i recall the scenario that = multiple processes share a AnonPage=20 > special case : >=20 > for example Process A have a AnonPage map like this: > ! pte_dirty() && PageDirty()=3D=3D1 (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: >=20 > A ! pte_dirty() && PageDirty() =3D=3D 0 && PageSwapCache() =3D=3D 0 >=20 > B ! pte_dirty() && PageDirty() =3D=3D 0 && PageSwapCache() =3D=3D 0 >=20 > This means this page is freeable , and can be freed during page = reclaim. > This is not fair for Process B . Since B don=E2=80=99t call = syscall(MADV_FREE) , > its page should not be discard . Will cause some strange behaviour if = happened . >=20 > This is discussed by=20 > http://www.serverphorums.com/read.php?12,1220840 > but i don=E2=80=99t know why the patch is not merged . >=20 > Thanks=20 oh, i have see 0b502297d1cc26e09b98955b4efa728be1c48921 this commit merged , then this problem should be fixed by this method. ignore this mail. :) Thanks a lot . -- 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