From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f45.google.com (mail-pa0-f45.google.com [209.85.220.45]) by kanga.kvack.org (Postfix) with ESMTP id 9358B6B0038 for ; Tue, 3 Mar 2015 08:31:40 -0500 (EST) Received: by padfa1 with SMTP id fa1so24020684pad.9 for ; Tue, 03 Mar 2015 05:31:40 -0800 (PST) Received: from e28smtp09.in.ibm.com (e28smtp09.in.ibm.com. [122.248.162.9]) by mx.google.com with ESMTPS id i2si963804pdc.145.2015.03.03.05.31.38 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 03 Mar 2015 05:31:39 -0800 (PST) Received: from /spool/local by e28smtp09.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 3 Mar 2015 19:01:36 +0530 Received: from d28relay02.in.ibm.com (d28relay02.in.ibm.com [9.184.220.59]) by d28dlp01.in.ibm.com (Postfix) with ESMTP id 35BB7E0044 for ; Tue, 3 Mar 2015 19:03:27 +0530 (IST) Received: from d28av04.in.ibm.com (d28av04.in.ibm.com [9.184.220.66]) by d28relay02.in.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id t23DR6CL40239208 for ; Tue, 3 Mar 2015 19:01:34 +0530 Received: from d28av04.in.ibm.com (localhost [127.0.0.1]) by d28av04.in.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id t23DLjdj009710 for ; Tue, 3 Mar 2015 18:51:45 +0530 From: "Aneesh Kumar K.V" Subject: Re: [PATCHv3 03/24] mm: avoid PG_locked on tail pages In-Reply-To: <54DD08BC.2020008@redhat.com> References: <1423757918-197669-1-git-send-email-kirill.shutemov@linux.intel.com> <1423757918-197669-4-git-send-email-kirill.shutemov@linux.intel.com> <54DD054E.7000605@redhat.com> <54DD08BC.2020008@redhat.com> Date: Tue, 03 Mar 2015 18:51:11 +0530 Message-ID: <87egp69pyw.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: To: Rik van Riel , "Kirill A. Shutemov" , Andrew Morton , Andrea Arcangeli , Hugh Dickins Cc: Dave Hansen , Mel Gorman , Vlastimil Babka , Christoph Lameter , Naoya Horiguchi , Steve Capper , Johannes Weiner , Michal Hocko , Jerome Marchand , linux-kernel@vger.kernel.org, linux-mm@kvack.org Rik van Riel writes: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > On 02/12/2015 02:55 PM, Rik van Riel wrote: >> On 02/12/2015 11:18 AM, Kirill A. Shutemov wrote: > >>> @@ -490,6 +493,7 @@ extern int >>> wait_on_page_bit_killable_timeout(struct page *page, >> >>> static inline int wait_on_page_locked_killable(struct page *page) >>> { + page = compound_head(page); if (PageLocked(page)) return >>> wait_on_page_bit_killable(page, PG_locked); return 0; @@ -510,6 >>> +514,7 @@ static inline void wake_up_page(struct page *page, int >>> bit) */ static inline void wait_on_page_locked(struct page *page) >>> { + page = compound_head(page); if (PageLocked(page)) >>> wait_on_page_bit(page, PG_locked); } >> >> These are all atomic operations. >> >> This may be a stupid question with the answer lurking somewhere in >> the other patches, but how do you ensure you operate on the right >> page lock during a THP collapse or split? > > Kirill answered that question on IRC. > > The VM takes a refcount on a page before attempting to take a page > lock, which prevents the THP code from doing anything with the > page. In other words, while we have a refcount on the page, we > will dereference the same page lock. Can we explain this more ? Don't we allow a thp split to happen even if we have page refcount ?. -aneesh -- 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