Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753373AbbB0Fs5 (ORCPT ); Fri, 27 Feb 2015 00:48:57 -0500 Received: from cnbjrel01.sonyericsson.com ([219.141.167.165]:3463 "EHLO cnbjrel01.sonyericsson.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750727AbbB0Fsz convert rfc822-to-8bit (ORCPT ); Fri, 27 Feb 2015 00:48:55 -0500 From: "Wang, Yalin" To: "'Minchan Kim'" CC: Michal Hocko , Andrew Morton , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Rik van Riel , Johannes Weiner , Mel Gorman , Shaohua Li Date: Fri, 27 Feb 2015 13:48:48 +0800 Subject: RE: [RFC] mm: change mm_advise_free to clear page dirty Thread-Topic: [RFC] mm: change mm_advise_free to clear page dirty Thread-Index: AdBSTjU831iKFtgMQlmLZz1gi/193wAAhHgg Message-ID: <35FD53F367049845BC99AC72306C23D10458D6173BDE@CNBJMBX05.corpusers.net> References: <1424765897-27377-1-git-send-email-minchan@kernel.org> <20150224154318.GA14939@dhcp22.suse.cz> <20150225000809.GA6468@blaptop> <35FD53F367049845BC99AC72306C23D10458D6173BDC@CNBJMBX05.corpusers.net> <20150227052805.GA20805@blaptop> In-Reply-To: <20150227052805.GA20805@blaptop> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2908 Lines: 83 > -----Original Message----- > From: Minchan Kim [mailto:minchan.kim@gmail.com] On Behalf Of Minchan Kim > Sent: Friday, February 27, 2015 1:28 PM > To: Wang, Yalin > Cc: Michal Hocko; Andrew Morton; linux-kernel@vger.kernel.org; linux- > mm@kvack.org; Rik van Riel; Johannes Weiner; Mel Gorman; Shaohua Li > Subject: Re: [RFC] mm: change mm_advise_free to clear page dirty > > Hello, > > On Fri, Feb 27, 2015 at 11:37:18AM +0800, Wang, Yalin wrote: > > This patch add ClearPageDirty() to clear AnonPage dirty flag, > > the Anonpage mapcount must be 1, so that this page is only used by > > the current process, not shared by other process like fork(). > > if not clear page dirty for this anon page, the page will never be > > treated as freeable. > > In case of anonymous page, it has PG_dirty when VM adds it to > swap cache and clear it in clear_page_dirty_for_io. That's why > I added ClearPageDirty if we found it in swapcache. > What case am I missing? It would be better to understand if you > describe specific scenario. > > Thanks. > > > > > Signed-off-by: Yalin Wang > > --- > > mm/madvise.c | 15 +++++---------- > > 1 file changed, 5 insertions(+), 10 deletions(-) > > > > diff --git a/mm/madvise.c b/mm/madvise.c > > index 6d0fcb8..257925a 100644 > > --- a/mm/madvise.c > > +++ b/mm/madvise.c > > @@ -297,22 +297,17 @@ static int madvise_free_pte_range(pmd_t *pmd, > unsigned long addr, > > continue; > > > > page = vm_normal_page(vma, addr, ptent); > > - if (!page) > > + if (!page || !PageAnon(page) || !trylock_page(page)) > > continue; > > > > if (PageSwapCache(page)) { > > - if (!trylock_page(page)) > > + if (!try_to_free_swap(page)) > > continue; > > - > > - if (!try_to_free_swap(page)) { > > - unlock_page(page); > > - continue; > > - } > > - > > - ClearPageDirty(page); > > - unlock_page(page); > > } > > > > + if (page_mapcount(page) == 1) > > + ClearPageDirty(page); > > + unlock_page(page); > > /* > > * Some of architecture(ex, PPC) don't update TLB > > * with set_pte_at and tlb_remove_tlb_entry so for > > -- Yes, for page which is in SwapCache, it is correct, But for anon page which is not in SwapCache, it is always PageDirty(), so we should also clear dirty bit to make it freeable, Another problem is that if an anon page is shared by more than one process, This happened when fork(), the anon page will be copy on write, In this case, we should not clear page dirty, Otherwise, other process will get zero page if the page is freed by reclaim path, This is not correct for other process which don't call MADV_FREE syscall. Thanks -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/