From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f181.google.com (mail-wi0-f181.google.com [209.85.212.181]) by kanga.kvack.org (Postfix) with ESMTP id DA21A6B0038 for ; Tue, 3 Mar 2015 08:35:42 -0500 (EST) Received: by wivr20 with SMTP id r20so22721933wiv.2 for ; Tue, 03 Mar 2015 05:35:42 -0800 (PST) Received: from kirsi1.inet.fi (mta-out1.inet.fi. [62.71.2.227]) by mx.google.com with ESMTP id di6si23917710wid.52.2015.03.03.05.35.40 for ; Tue, 03 Mar 2015 05:35:41 -0800 (PST) Date: Tue, 3 Mar 2015 15:35:24 +0200 From: "Kirill A. Shutemov" Subject: Re: [PATCHv3 03/24] mm: avoid PG_locked on tail pages Message-ID: <20150303133524.GA6111@node.dhcp.inet.fi> 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> <87egp69pyw.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87egp69pyw.fsf@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Aneesh Kumar K.V" Cc: Rik van Riel , "Kirill A. Shutemov" , Andrew Morton , Andrea Arcangeli , Hugh Dickins , 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 On Tue, Mar 03, 2015 at 06:51:11PM +0530, Aneesh Kumar K.V wrote: > 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 ?. The patchset changes this. Have you read the cover letter? -- Kirill A. Shutemov -- 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