Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757959AbZIPAIX (ORCPT ); Tue, 15 Sep 2009 20:08:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753099AbZIPAIS (ORCPT ); Tue, 15 Sep 2009 20:08:18 -0400 Received: from fgwmail7.fujitsu.co.jp ([192.51.44.37]:52252 "EHLO fgwmail7.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753141AbZIPAIR (ORCPT ); Tue, 15 Sep 2009 20:08:17 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 From: KOSAKI Motohiro To: Hugh Dickins Subject: Re: [PATCH 1/4] mm: m(un)lock avoid ZERO_PAGE Cc: kosaki.motohiro@jp.fujitsu.com, Andrew Morton , KAMEZAWA Hiroyuki , Linus Torvalds , Nick Piggin , Rik van Riel , Mel Gorman , Minchan Kim , linux-kernel@vger.kernel.org, linux-mm@kvack.org In-Reply-To: References: Message-Id: <20090916090348.DB89.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.50.07 [ja] Date: Wed, 16 Sep 2009 09:08:15 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2594 Lines: 69 > I'm still reluctant to clutter __get_user_pages() with another flag, > just to avoid touching ZERO_PAGE count in mlock(); though we can add > that later if it shows up as an issue in practice. > > But when mlocking, we can test page->mapping slightly earlier, to avoid > the potentially bouncy rescheduling of lock_page on ZERO_PAGE - mlock > didn't lock_page in olden ZERO_PAGE days, so we might have regressed. > > And when munlocking, it turns out that FOLL_DUMP coincidentally does > what's needed to avoid all updates to ZERO_PAGE, so use that here also. > Plus add comment suggested by KAMEZAWA Hiroyuki. > > Signed-off-by: Hugh Dickins > --- > > mm/mlock.c | 49 ++++++++++++++++++++++++++++++++++++------------- > 1 file changed, 36 insertions(+), 13 deletions(-) > > --- mm0/mm/mlock.c 2009-09-14 16:34:37.000000000 +0100 > +++ mm1/mm/mlock.c 2009-09-15 17:32:03.000000000 +0100 > @@ -198,17 +198,26 @@ static long __mlock_vma_pages_range(stru > for (i = 0; i < ret; i++) { > struct page *page = pages[i]; > > - lock_page(page); > - /* > - * Because we lock page here and migration is blocked > - * by the elevated reference, we need only check for > - * file-cache page truncation. This page->mapping > - * check also neatly skips over the ZERO_PAGE(), > - * though if that's common we'd prefer not to lock it. > - */ > - if (page->mapping) > - mlock_vma_page(page); > - unlock_page(page); > + if (page->mapping) { > + /* > + * That preliminary check is mainly to avoid > + * the pointless overhead of lock_page on the > + * ZERO_PAGE: which might bounce very badly if > + * there is contention. However, we're still > + * dirtying its cacheline with get/put_page: > + * we'll add another __get_user_pages flag to > + * avoid it if that case turns out to matter. > + */ > + lock_page(page); > + /* > + * Because we lock page here and migration is > + * blocked by the elevated reference, we need > + * only check for file-cache page truncation. > + */ > + if (page->mapping) > + mlock_vma_page(page); > + unlock_page(page); > + } > put_page(page); /* ref from get_user_pages() */ > } Yes, I have similar patch :-) Reviewed-by: KOSAKI Motohiro -- 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/