From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id EC85E8D0041 for ; Tue, 1 Feb 2011 11:10:01 -0500 (EST) Date: Tue, 1 Feb 2011 17:09:32 +0100 From: Andrea Arcangeli Subject: Re: [RFC][PATCH 5/6] teach smaps_pte_range() about THP pmds Message-ID: <20110201160932.GY16981@random.random> References: <20110201003357.D6F0BE0D@kernel> <20110201003403.736A24DF@kernel> <20110201101111.GK19534@cmpxchg.org> <1296572550.27022.2862.camel@nimitz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1296572550.27022.2862.camel@nimitz> Sender: owner-linux-mm@kvack.org To: Dave Hansen Cc: Johannes Weiner , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Michael J Wolf List-ID: On Tue, Feb 01, 2011 at 07:02:30AM -0800, Dave Hansen wrote: > On Tue, 2011-02-01 at 11:11 +0100, Johannes Weiner wrote: > > On Mon, Jan 31, 2011 at 04:34:03PM -0800, Dave Hansen wrote: > > > + if (pmd_trans_huge(*pmd)) { > > > + if (pmd_trans_splitting(*pmd)) { > > > + spin_unlock(&walk->mm->page_table_lock); > > > + wait_split_huge_page(vma->anon_vma, pmd); > > > + spin_lock(&walk->mm->page_table_lock); > > > + goto normal_ptes; > > > + } > > > + smaps_pte_entry(*(pte_t *)pmd, addr, HPAGE_SIZE, walk); > > > + return 0; > > > + } > > > +normal_ptes: > > > split_huge_page_pmd(walk->mm, pmd); > > > > This line can go away now...? > > I did this because I was unsure what keeps khugepaged away from the > newly-split ptes between the wait_split_huge_page() and the > reacquisition of the mm->page_table_lock. mmap_sem, perhaps? Any of mmap_sem read mode, PG_lock and anon_vma_lock keeps khugepaged away. > Looking at follow_page() and some of the other wait_split_huge_page(), > it looks like this is unnecessary. When wait_split_huge_page returns after the pmd was splitting, the pmd can't return huge under you as long as you hold any of the above. -- 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/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org