From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f46.google.com (mail-pa0-f46.google.com [209.85.220.46]) by kanga.kvack.org (Postfix) with ESMTP id 81D3F6B0038 for ; Tue, 27 Oct 2015 04:52:14 -0400 (EDT) Received: by pabla5 with SMTP id la5so23371763pab.0 for ; Tue, 27 Oct 2015 01:52:14 -0700 (PDT) Received: from mail-pa0-x234.google.com (mail-pa0-x234.google.com. [2607:f8b0:400e:c03::234]) by mx.google.com with ESMTPS id ku5si60282041pbc.25.2015.10.27.01.52.13 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 27 Oct 2015 01:52:13 -0700 (PDT) Received: by pasz6 with SMTP id z6so216223943pas.2 for ; Tue, 27 Oct 2015 01:52:13 -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: <20151027081059.GE26803@bbox> Date: Tue, 27 Oct 2015 16:52:07 +0800 Content-Transfer-Encoding: quoted-printable Message-Id: 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 16:10, 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=99t= 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! i have a look at the old mail list , i recall the scenario that multiple = processes share a AnonPage=20 special case : 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: A ! pte_dirty() && PageDirty() =3D=3D 0 && PageSwapCache() =3D=3D 0 B ! pte_dirty() && PageDirty() =3D=3D 0 && PageSwapCache() =3D=3D 0 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 . 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 . Thanks=20 -- 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