Return-Path: linux-nfs-owner@vger.kernel.org Received: from mail-pa0-f45.google.com ([209.85.220.45]:54902 "EHLO mail-pa0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755399AbaKUKPK (ORCPT ); Fri, 21 Nov 2014 05:15:10 -0500 Received: by mail-pa0-f45.google.com with SMTP id lj1so4590893pab.32 for ; Fri, 21 Nov 2014 02:15:10 -0800 (PST) From: Omar Sandoval To: Alexander Viro , Andrew Morton , Chris Mason , Josef Bacik , linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-nfs@vger.kernel.org, Trond Myklebust , Mel Gorman Cc: Omar Sandoval Subject: [PATCH v2 0/5] btrfs: implement swap file support Date: Fri, 21 Nov 2014 02:08:26 -0800 Message-Id: Sender: linux-nfs-owner@vger.kernel.org List-ID: This patch series, based on 3.18-rc5, implements support for swap files on BTRFS. The standard swap file implementation uses the filesystem's implementation of bmap() to get a list of physical blocks on disk, which the swap file code then does I/O on directly without going through the filesystem. This doesn't work for BTRFS, which is copy-on-write and therefore moves disk blocks around (COW isn't the only thing that can shuffle around disk blocks: consider defragmentation, balancing, etc.). Swap-over-NFS introduced an interface through which a filesystem can arbitrate swap I/O through address space operations: - swap_activate() is called by swapon() and informs the address space that the given file is going to be used for swap, so it should take adequate measures like reserving space on disk and pinning block lookup information in memory - swap_deactivate() is used to clean up on swapoff() - readpage() is used to page in (read a page from disk) - direct_IO() is used to page out (write a page out to disk) Version 2 modifies this interface in the first part of the patch series to use direct_IO for both reads and writes, which makes things much cleaner. The second part of the patch series implements support for the interface on BTRFS, which just means implementing swap_{,de}activate and adding some chattr checks, which raises the following considerations: - We can't do direct I/O on compressed or inline extents, so we can't use files with either for swap. - Supporting COW swapfiles might also come with some weird edge cases? This functionality is tenuously tested in a virtual machine with some artificial workloads. Comment away. Omar Sandoval (5): direct-io: don't dirty ITER_BVEC pages on read nfs: don't dirty ITER_BVEC pages read through direct I/O swap: use direct I/O for SWP_FILE swap_readpage btrfs: don't allow -C or +c chattrs on a swap file btrfs: enable swap file support v2: use direct_IO for swap_readpage fs/btrfs/inode.c | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ fs/btrfs/ioctl.c | 50 ++++++++++++++++++++++++--------------- fs/direct-io.c | 8 ++++--- fs/nfs/direct.c | 5 +++- mm/page_io.c | 32 +++++++++++++++++++++---- 5 files changed, 139 insertions(+), 27 deletions(-) -- 2.1.3