From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758583Ab0DACnU (ORCPT ); Wed, 31 Mar 2010 22:43:20 -0400 Received: from mail-pv0-f174.google.com ([74.125.83.174]:41112 "EHLO mail-pv0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752882Ab0DACnT convert rfc822-to-8bit (ORCPT ); Wed, 31 Mar 2010 22:43:19 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=xBv45LLgEumTfzGuuUYznK8s2NVPfuKHqnTFlb4xd+zJ06hOepL0nzHYYUhwUldGRx h2PDmx4krJ+teMxCuEsFxD+VT2zmzCC8ElfcDQm3zovjaxtLoqyCFLXFHGIg4dBb06QE T8EknOmaruIeXRn1c8fODy9SpqBSaBGRbEZVU= MIME-Version: 1.0 In-Reply-To: <20100331142623.62ac9175.kamezawa.hiroyu@jp.fujitsu.com> References: <1269940489-5776-1-git-send-email-mel@csn.ul.ie> <1269940489-5776-15-git-send-email-mel@csn.ul.ie> <20100331142623.62ac9175.kamezawa.hiroyu@jp.fujitsu.com> Date: Thu, 1 Apr 2010 11:43:18 +0900 Message-ID: Subject: Re: [PATCH 14/14] mm,migration: Allow the migration of PageSwapCache pages From: Minchan Kim To: KAMEZAWA Hiroyuki Cc: Mel Gorman , Andrew Morton , Andrea Arcangeli , Christoph Lameter , Adam Litke , Avi Kivity , David Rientjes , KOSAKI Motohiro , Rik van Riel , linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 31, 2010 at 2:26 PM, KAMEZAWA Hiroyuki wrote: > On Tue, 30 Mar 2010 10:14:49 +0100 > Mel Gorman wrote: > >> PageAnon pages that are unmapped may or may not have an anon_vma so >> are not currently migrated. However, a swap cache page can be migrated >> and fits this description. This patch identifies page swap caches and >> allows them to be migrated. >> > > Some comments. > >> Signed-off-by: Mel Gorman >> --- >>  mm/migrate.c |   15 ++++++++++----- >>  mm/rmap.c    |    6 ++++-- >>  2 files changed, 14 insertions(+), 7 deletions(-) >> >> diff --git a/mm/migrate.c b/mm/migrate.c >> index 35aad2a..f9bf37e 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -203,6 +203,9 @@ static int migrate_page_move_mapping(struct address_space *mapping, >>       void **pslot; >> >>       if (!mapping) { >> +             if (PageSwapCache(page)) >> +                     SetPageSwapCache(newpage); >> + > > Migration of SwapCache requires radix-tree replacement, IOW, >  mapping == NULL && PageSwapCache is BUG. > > So, this never happens. > > >>               /* Anonymous page without mapping */ >>               if (page_count(page) != 1) >>                       return -EAGAIN; >> @@ -607,11 +610,13 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private, >>                * the page was isolated and when we reached here while >>                * the RCU lock was not held >>                */ >> -             if (!page_mapped(page)) >> -                     goto rcu_unlock; >> - >> -             anon_vma = page_anon_vma(page); >> -             atomic_inc(&anon_vma->external_refcount); >> +             if (!page_mapped(page)) { >> +                     if (!PageSwapCache(page)) >> +                             goto rcu_unlock; >> +             } else { >> +                     anon_vma = page_anon_vma(page); >> +                     atomic_inc(&anon_vma->external_refcount); >> +             } >>       } >> >>       /* >> diff --git a/mm/rmap.c b/mm/rmap.c >> index af35b75..d5ea1f2 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -1394,9 +1394,11 @@ int rmap_walk(struct page *page, int (*rmap_one)(struct page *, >> >>       if (unlikely(PageKsm(page))) >>               return rmap_walk_ksm(page, rmap_one, arg); >> -     else if (PageAnon(page)) >> +     else if (PageAnon(page)) { >> +             if (PageSwapCache(page)) >> +                     return SWAP_AGAIN; >>               return rmap_walk_anon(page, rmap_one, arg); > > SwapCache has a condition as (PageSwapCache(page) && page_mapped(page) == true. > In case of tmpfs, page has swapcache but not mapped. > Please see do_swap_page(), PageSwapCache bit is cleared only when > > do_swap_page()... >       swap_free(entry); >        if (vm_swap_full() || (vma->vm_flags & VM_LOCKED) || PageMlocked(page)) >                try_to_free_swap(page); > > Then, PageSwapCache is cleared only when swap is freeable even if mapped. > > rmap_walk_anon() should be called and the check is not necessary. Frankly speaking, I don't understand what is Mel's problem, why he added Swapcache check in rmap_walk, and why do you said we don't need it. Could you explain more detail if you don't mind? > > Thanks, > -Kame > > -- Kind regards, Minchan Kim