Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754776AbbB0Goi (ORCPT ); Fri, 27 Feb 2015 01:44:38 -0500 Received: from mail-pa0-f50.google.com ([209.85.220.50]:37298 "EHLO mail-pa0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750875AbbB0Gog (ORCPT ); Fri, 27 Feb 2015 01:44:36 -0500 Date: Fri, 27 Feb 2015 15:44:25 +0900 From: Minchan Kim 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 Message-ID: <20150227064425.GB20805@blaptop> 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> <35FD53F367049845BC99AC72306C23D10458D6173BDE@CNBJMBX05.corpusers.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <35FD53F367049845BC99AC72306C23D10458D6173BDE@CNBJMBX05.corpusers.net> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3952 Lines: 122 On Fri, Feb 27, 2015 at 01:48:48PM +0800, Wang, Yalin wrote: > > -----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, No. Every anon page starts from !PageDirty and it has PG_dirty only when it's addeded into swap cache. If vm_swap_full turns on, a page in swap cache could have PG_dirty via try_to_free_swap again. So, Do you have concern about swapped-out pages when MADV_FREE is called? If so, please look at my patch. https://lkml.org/lkml/2015/2/25/43 It will zap the swapped out page. So, this is not a issue any more? > > 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, > This is not correct for other process which don't call MADV_FREE syscall. You mean we shouldn't inherit MADV_FREE attribute? Why? parent: ptr1 = malloc(len); -> allocator calls mmap(len); memset(ptr1, 'a', len); free(ptr1); -> allocator calss madvise_free(ptr1, len); .. .. -> VM discard hinted pages fork(); child: ptr2 = malloc(len) -> allocator reuses the chunk allocated from parent. so, child will see zero pages from ptr2 but he doesn't write anything so garbage|zero page anything is okay to him. > > Thanks > > -- Kind regards, Minchan Kim -- 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/