From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753378Ab0DADFR (ORCPT ); Wed, 31 Mar 2010 23:05:17 -0400 Received: from fgwmail7.fujitsu.co.jp ([192.51.44.37]:50882 "EHLO fgwmail7.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751591Ab0DADFO (ORCPT ); Wed, 31 Mar 2010 23:05:14 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Date: Thu, 1 Apr 2010 12:01:23 +0900 From: KAMEZAWA Hiroyuki To: Minchan Kim 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 Subject: Re: [PATCH 14/14] mm,migration: Allow the migration of PageSwapCache pages Message-Id: <20100401120123.f9f9e872.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: 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> Organization: FUJITSU Co. LTD. X-Mailer: Sylpheed 3.0.1 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 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 Thu, 1 Apr 2010 11:43:18 +0900 Minchan Kim wrote: > On Wed, Mar 31, 2010 at 2:26 PM, KAMEZAWA Hiroyuki       /* > >> 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? > I may miss something. unmap_and_move() 1. try_to_unmap(TTU_MIGRATION) 2. move_to_newpage 3. remove_migration_ptes -> rmap_walk() Then, to map a page back we unmapped we call rmap_walk(). Assume a SwapCache which is mapped, then, PageAnon(page) == true. At 1. try_to_unmap() will rewrite pte with swp_entry of SwapCache. mapcount goes to 0. At 2. SwapCache is copied to a new page. At 3. The new page is mapped back to the place. Now, newpage's mapcount is 0. Before patch, the new page is mapped back to all ptes. After patch, the new page is not mapped back because its mapcount is 0. I don't think shared SwapCache of anon is not an usual behavior, so, the logic before patch is more attractive. If SwapCache is not mapped before "1", we skip "1" and rmap_walk will do nothing because page->mapping is NULL. Thanks, -Kame From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with SMTP id 149346B01EE for ; Wed, 31 Mar 2010 23:05:16 -0400 (EDT) Received: from m2.gw.fujitsu.co.jp ([10.0.50.72]) by fgwmail7.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o3135DYw020420 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Thu, 1 Apr 2010 12:05:13 +0900 Received: from smail (m2 [127.0.0.1]) by outgoing.m2.gw.fujitsu.co.jp (Postfix) with ESMTP id E19FF45DE4F for ; Thu, 1 Apr 2010 12:13:43 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (s2.gw.fujitsu.co.jp [10.0.50.92]) by m2.gw.fujitsu.co.jp (Postfix) with ESMTP id E19FF45DE62 for ; Thu, 1 Apr 2010 12:13:43 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id B7AD1E3800F for ; Thu, 1 Apr 2010 12:05:12 +0900 (JST) Received: from ml13.s.css.fujitsu.com (ml13.s.css.fujitsu.com [10.249.87.103]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id 96576E38009 for ; Thu, 1 Apr 2010 12:05:11 +0900 (JST) Date: Thu, 1 Apr 2010 12:01:23 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH 14/14] mm,migration: Allow the migration of PageSwapCache pages Message-Id: <20100401120123.f9f9e872.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: 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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org To: Minchan Kim 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 List-ID: On Thu, 1 Apr 2010 11:43:18 +0900 Minchan Kim wrote: > On Wed, Mar 31, 2010 at 2:26 PM, KAMEZAWA Hiroyuki A A A /* > >> 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 *, > >> > >> A A A if (unlikely(PageKsm(page))) > >> A A A A A A A return rmap_walk_ksm(page, rmap_one, arg); > >> - A A else if (PageAnon(page)) > >> + A A else if (PageAnon(page)) { > >> + A A A A A A if (PageSwapCache(page)) > >> + A A A A A A A A A A return SWAP_AGAIN; > >> A A A A A A A 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()... > > A A A swap_free(entry); > > A A A A if (vm_swap_full() || (vma->vm_flags & VM_LOCKED) || PageMlocked(page)) > > A A A A A A A A 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? > I may miss something. unmap_and_move() 1. try_to_unmap(TTU_MIGRATION) 2. move_to_newpage 3. remove_migration_ptes -> rmap_walk() Then, to map a page back we unmapped we call rmap_walk(). Assume a SwapCache which is mapped, then, PageAnon(page) == true. At 1. try_to_unmap() will rewrite pte with swp_entry of SwapCache. mapcount goes to 0. At 2. SwapCache is copied to a new page. At 3. The new page is mapped back to the place. Now, newpage's mapcount is 0. Before patch, the new page is mapped back to all ptes. After patch, the new page is not mapped back because its mapcount is 0. I don't think shared SwapCache of anon is not an usual behavior, so, the logic before patch is more attractive. If SwapCache is not mapped before "1", we skip "1" and rmap_walk will do nothing because page->mapping is NULL. Thanks, -Kame -- 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