Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1946038AbbEON3k (ORCPT ); Fri, 15 May 2015 09:29:40 -0400 Received: from mta-out1.inet.fi ([62.71.2.227]:33711 "EHLO kirsi1.inet.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1422869AbbEON3j (ORCPT ); Fri, 15 May 2015 09:29:39 -0400 Date: Fri, 15 May 2015 16:29:11 +0300 From: "Kirill A. Shutemov" To: Vlastimil Babka Cc: "Kirill A. Shutemov" , Andrew Morton , Andrea Arcangeli , Hugh Dickins , Dave Hansen , Mel Gorman , Rik van Riel , Christoph Lameter , Naoya Horiguchi , Steve Capper , "Aneesh Kumar K.V" , Johannes Weiner , Michal Hocko , Jerome Marchand , Sasha Levin , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCHv5 04/28] mm, thp: adjust conditions when we can reuse the page on WP fault Message-ID: <20150515132911.GA6625@node.dhcp.inet.fi> References: <1429823043-157133-1-git-send-email-kirill.shutemov@linux.intel.com> <1429823043-157133-5-git-send-email-kirill.shutemov@linux.intel.com> <5555B914.8050800@suse.cz> <20150515112113.GD6250@node.dhcp.inet.fi> <5555DA15.10903@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5555DA15.10903@suse.cz> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2765 Lines: 70 On Fri, May 15, 2015 at 01:35:49PM +0200, Vlastimil Babka wrote: > On 05/15/2015 01:21 PM, Kirill A. Shutemov wrote: > >On Fri, May 15, 2015 at 11:15:00AM +0200, Vlastimil Babka wrote: > >>On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote: > >>>With new refcounting we will be able map the same compound page with > >>>PTEs and PMDs. It requires adjustment to conditions when we can reuse > >>>the page on write-protection fault. > >>> > >>>For PTE fault we can't reuse the page if it's part of huge page. > >>> > >>>For PMD we can only reuse the page if nobody else maps the huge page or > >>>it's part. We can do it by checking page_mapcount() on each sub-page, > >>>but it's expensive. > >>> > >>>The cheaper way is to check page_count() to be equal 1: every mapcount > >>>takes page reference, so this way we can guarantee, that the PMD is the > >>>only mapping. > >>> > >>>This approach can give false negative if somebody pinned the page, but > >>>that doesn't affect correctness. > >>> > >>>Signed-off-by: Kirill A. Shutemov > >>>Tested-by: Sasha Levin > >> > >>Acked-by: Vlastimil Babka > >> > >>So couldn't the same trick be used in Patch 1 to avoid counting individual > >>oder-0 pages? > > > >Hm. You're right, we could. But is smaps that performance sensitive to > >bother? > > Well, I was nudged to optimize it when doing the shmem swap accounting > changes there :) User may not care about the latency of obtaining the smaps > file contents, but since it has mmap_sem locked for that, the process might > care... Somewthing like this? diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index e04399e53965..5bc3d2b1176e 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -462,6 +462,19 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page, if (young || PageReferenced(page)) mss->referenced += size; + /* + * page_count(page) == 1 guarantees the page is mapped exactly once. + * If any subpage of the compound page mapped with PTE it would elevate + * page_count(). + */ + if (page_count(page) == 1) { + if (dirty || PageDirty(page)) + mss->private_dirty += size; + else + mss->private_clean += size; + return; + } + for (i = 0; i < nr; i++, page++) { int mapcount = page_mapcount(page); -- Kirill A. Shutemov -- 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/