Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754907AbaBRSCb (ORCPT ); Tue, 18 Feb 2014 13:02:31 -0500 Received: from mail-ve0-f172.google.com ([209.85.128.172]:38953 "EHLO mail-ve0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754344AbaBRSC1 (ORCPT ); Tue, 18 Feb 2014 13:02:27 -0500 MIME-Version: 1.0 In-Reply-To: <100D68C7BA14664A8938383216E40DE04062DEA1@FMSMSX114.amr.corp.intel.com> References: <1392662333-25470-1-git-send-email-kirill.shutemov@linux.intel.com> <53035FE2.4080300@redhat.com> <100D68C7BA14664A8938383216E40DE04062DEA1@FMSMSX114.amr.corp.intel.com> Date: Tue, 18 Feb 2014 10:02:26 -0800 X-Google-Sender-Auth: z_v864ZoM7GgVzBFl_eF_zb50j4 Message-ID: Subject: Re: [RFC, PATCHv2 0/2] mm: map few pages around fault address if they are in page cache From: Linus Torvalds To: "Wilcox, Matthew R" Cc: Rik van Riel , "Kirill A. Shutemov" , Andrew Morton , Mel Gorman , Andi Kleen , Dave Hansen , Alexander Viro , Dave Chinner , linux-mm , linux-fsdevel , Linux Kernel Mailing List Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 18, 2014 at 6:15 AM, Wilcox, Matthew R wrote: > We don't really need to lock all the pages being returned to protect against truncate. We only need to lock the one at the highest index, and check i_size while that lock is held since truncate_inode_pages_range() will block on any page that is locked. > > We're still vulnerable to holepunches, but there's no locking currently between holepunches and truncate, so we're no worse off now. It's not "holepunches and truncate", it's "holepunches and page mapping", and I do think we currently serialize the two - the whole "check page->mapping still being non-NULL" before mapping it while having the page locked does that. Besides, that per-page locking should serialize against truncate too. No, there is no "global" serialization, but there *is* exactly that page-level serialization where both truncation and hole punching end up making sure that the page no longer exists in the page cache and isn't mapped. I'm just claiming that *because* of the way rmap works for file mappings (walking the i_mapped list and page tables), we should actually be ok. The anonymous rmap list is protected by the page lock, but the file-backed rmap is protected by the pte lock (well, and the "i_mmap_mutex" that in turn protects the i_mmap list etc). Linus -- 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/