From patchwork Fri Nov 2 09:06:07 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: ethanlien X-Patchwork-Id: 10665159 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 0337915E9 for ; Fri, 2 Nov 2018 09:06:23 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id DF6F22B664 for ; Fri, 2 Nov 2018 09:06:22 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id D01022B907; Fri, 2 Nov 2018 09:06:22 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 1F2FA2B664 for ; Fri, 2 Nov 2018 09:06:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726370AbeKBSMt (ORCPT ); Fri, 2 Nov 2018 14:12:49 -0400 Received: from synology.com ([59.124.61.242]:56087 "EHLO synology.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726049AbeKBSMs (ORCPT ); Fri, 2 Nov 2018 14:12:48 -0400 Received: from localhost.localdomain (unknown [10.13.23.103]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-SHA256 (128/128 bits)) (No client certificate requested) by synology.com (Postfix) with ESMTPSA id A4C1122C02DB; Fri, 2 Nov 2018 17:06:18 +0800 (CST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=synology.com; s=123; t=1541149578; bh=jY2tSFrwYJ3bhrtQJ0xlzwBu30ZEEBFBe2FJQlF+hZU=; h=From:To:Cc:Subject:Date; b=ol00oGQGNp2WVMUdkzPFsuORcr4lpqRTiq96VZuZc/R6NqmANyXQuNcQADWcC4GG0 GT215W43DuGbvj03QJ2IEVJoscyDoChSF5rnn6WG2ckVLIGOocVuvB39JG5SsV6JKF oqhEJ29w5rEi1r6Rn2k5D/yDWDufxiPV637Eb3Eg= From: Ethan Lien To: linux-btrfs@vger.kernel.org Cc: Ethan Lien Subject: [PATCH v2] btrfs: use tagged writepage to mitigate livelock of snapshot Date: Fri, 2 Nov 2018 17:06:07 +0800 Message-Id: <20181102090607.19804-1-ethanlien@synology.com> X-Mailer: git-send-email 2.19.1 MIME-Version: 1.0 X-Synology-MCP-Status: no X-Synology-Spam-Flag: no X-Synology-Spam-Status: score=0, required 6, WHITELIST_FROM_ADDRESS 0 X-Synology-Virus-Status: no Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Snapshot is expected to be fast. But if there are writers steadily create dirty pages in our subvolume, the snapshot may take a very long time to complete. To fix the problem, we use tagged writepage for snapshot flusher as we do in generic write_cache_pages(): we quickly tag all dirty pages with a TOWRITE tag, then do the hard work of writepage only on those pages with TOWRITE tag, so we ommit pages dirtied after the snapshot command. We do a simple snapshot speed test on a Intel D-1531 box: fio --ioengine=libaio --iodepth=32 --bs=4k --rw=write --size=64G --direct=0 --thread=1 --numjobs=1 --time_based --runtime=120 --filename=/mnt/sub/testfile --name=job1 --group_reporting & sleep 5; time btrfs sub snap -r /mnt/sub /mnt/snap; killall fio original: 1m58sec patched: 6.54sec This is the best case for this patch since for a sequential write case, we omit nearly all pages dirtied after the snapshot command. For a multi writers, random write test: fio --ioengine=libaio --iodepth=32 --bs=4k --rw=randwrite --size=64G --direct=0 --thread=1 --numjobs=4 --time_based --runtime=120 --filename=/mnt/sub/testfile --name=job1 --group_reporting & sleep 5; time btrfs sub snap -r /mnt/sub /mnt/snap; killall fio original: 15.83sec patched: 10.35sec The improvement is less compared with the sequential write case, since we omit only half of the pages dirtied after snapshot command. Signed-off-by: Ethan Lien Reviewed-by: Nikolay Borisov --- V2: Add more details in commit message. rename BTRFS_INODE_TAGGED_FLUSH to BTRFS_INODE_SNAPSHOT_FLUSH. remove unnecessary sync_mode check. start_delalloc_inodes use boolean argument. fs/btrfs/btrfs_inode.h | 1 + fs/btrfs/ctree.h | 2 +- fs/btrfs/extent_io.c | 14 ++++++++++++-- fs/btrfs/inode.c | 10 ++++++---- fs/btrfs/ioctl.c | 2 +- 5 files changed, 21 insertions(+), 8 deletions(-) diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h index 1343ac57b438..ffc9a1c77375 100644 --- a/fs/btrfs/btrfs_inode.h +++ b/fs/btrfs/btrfs_inode.h @@ -29,6 +29,7 @@ enum { BTRFS_INODE_IN_DELALLOC_LIST, BTRFS_INODE_READDIO_NEED_LOCK, BTRFS_INODE_HAS_PROPS, + BTRFS_INODE_SNAPSHOT_FLUSH, }; /* in memory btrfs inode */ diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h index 2cddfe7806a4..82682da5a40d 100644 --- a/fs/btrfs/ctree.h +++ b/fs/btrfs/ctree.h @@ -3155,7 +3155,7 @@ int btrfs_truncate_inode_items(struct btrfs_trans_handle *trans, struct inode *inode, u64 new_size, u32 min_type); -int btrfs_start_delalloc_inodes(struct btrfs_root *root); +int btrfs_start_delalloc_snapshot(struct btrfs_root *root); int btrfs_start_delalloc_roots(struct btrfs_fs_info *fs_info, int nr); int btrfs_set_extent_delalloc(struct inode *inode, u64 start, u64 end, unsigned int extra_bits, diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 4dd6faab02bb..93f2e413535d 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -3928,12 +3928,22 @@ static int extent_write_cache_pages(struct address_space *mapping, range_whole = 1; scanned = 1; } - if (wbc->sync_mode == WB_SYNC_ALL) + + /* + * We do the tagged writepage as long as the snapshot flush bit is set + * and we are the first one who do the filemap_flush() on this inode. + */ + if (range_whole && wbc->nr_to_write == LONG_MAX && + test_and_clear_bit(BTRFS_INODE_SNAPSHOT_FLUSH, + &BTRFS_I(inode)->runtime_flags)) + wbc->tagged_writepages = 1; + + if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) tag = PAGECACHE_TAG_TOWRITE; else tag = PAGECACHE_TAG_DIRTY; retry: - if (wbc->sync_mode == WB_SYNC_ALL) + if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) tag_pages_for_writeback(mapping, index, end); done_index = index; while (!done && !nr_to_write_done && (index <= end) && diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 3ea5339603cf..593445d122ed 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -9975,7 +9975,7 @@ static struct btrfs_delalloc_work *btrfs_alloc_delalloc_work(struct inode *inode * some fairly slow code that needs optimization. This walks the list * of all the inodes with pending delalloc and forces them to disk. */ -static int start_delalloc_inodes(struct btrfs_root *root, int nr) +static int start_delalloc_inodes(struct btrfs_root *root, int nr, bool snapshot) { struct btrfs_inode *binode; struct inode *inode; @@ -10003,6 +10003,8 @@ static int start_delalloc_inodes(struct btrfs_root *root, int nr) } spin_unlock(&root->delalloc_lock); + if (snapshot) + set_bit(BTRFS_INODE_SNAPSHOT_FLUSH, &binode->runtime_flags); work = btrfs_alloc_delalloc_work(inode); if (!work) { iput(inode); @@ -10036,7 +10038,7 @@ static int start_delalloc_inodes(struct btrfs_root *root, int nr) return ret; } -int btrfs_start_delalloc_inodes(struct btrfs_root *root) +int btrfs_start_delalloc_snapshot(struct btrfs_root *root) { struct btrfs_fs_info *fs_info = root->fs_info; int ret; @@ -10044,7 +10046,7 @@ int btrfs_start_delalloc_inodes(struct btrfs_root *root) if (test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state)) return -EROFS; - ret = start_delalloc_inodes(root, -1); + ret = start_delalloc_inodes(root, -1, true); if (ret > 0) ret = 0; return ret; @@ -10073,7 +10075,7 @@ int btrfs_start_delalloc_roots(struct btrfs_fs_info *fs_info, int nr) &fs_info->delalloc_roots); spin_unlock(&fs_info->delalloc_root_lock); - ret = start_delalloc_inodes(root, nr); + ret = start_delalloc_inodes(root, nr, false); btrfs_put_fs_root(root); if (ret < 0) goto out; diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index d60b6caf09e8..d1293b6c31f6 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -775,7 +775,7 @@ static int create_snapshot(struct btrfs_root *root, struct inode *dir, wait_event(root->subv_writers->wait, percpu_counter_sum(&root->subv_writers->counter) == 0); - ret = btrfs_start_delalloc_inodes(root); + ret = btrfs_start_delalloc_snapshot(root); if (ret) goto dec_and_free;