From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5958BC0044C for ; Thu, 1 Nov 2018 06:49:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B4C9B2064C for ; Thu, 1 Nov 2018 06:49:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=synology.com header.i=@synology.com header.b="kLVj3R+4" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B4C9B2064C Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=synology.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-btrfs-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727742AbeKAPvY (ORCPT ); Thu, 1 Nov 2018 11:51:24 -0400 Received: from synology.com ([59.124.61.242]:41202 "EHLO synology.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727573AbeKAPvY (ORCPT ); Thu, 1 Nov 2018 11:51:24 -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 BA20D24D56A5; Thu, 1 Nov 2018 14:49:42 +0800 (CST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=synology.com; s=123; t=1541054982; bh=NNgEjOj5JcswsR3O3uOLIzUTTn2S9GUdlZv7v6KvTuU=; h=From:To:Cc:Subject:Date; b=kLVj3R+4M454FkKQsnMM0s4JrreXHsFXd3MzA9Ug/tNur/HXpsijzjDtpvrtBONMN q9IlUYX3Jt1MfWMRoVct135QopMJiPNPL3SKL3j7UeGgkW3zrximZZvBEaREHY0mpo wzwJdZglp+1m4dZRGyBgyAuIT1V3Tx8UpNy2PN2A= From: Ethan Lien To: linux-btrfs@vger.kernel.org Cc: Ethan Lien Subject: [PATCH] btrfs: use tagged writepage to mitigate livelock of snapshot Date: Thu, 1 Nov 2018 14:49:03 +0800 Message-Id: <20181101064903.11638-1-ethanlien@synology.com> X-Mailer: git-send-email 2.19.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 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 the generic write_cache_pages(), so we can 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 --- fs/btrfs/btrfs_inode.h | 1 + fs/btrfs/ctree.h | 2 +- fs/btrfs/extent_io.c | 16 ++++++++++++++-- fs/btrfs/inode.c | 10 ++++++---- fs/btrfs/ioctl.c | 2 +- 5 files changed, 23 insertions(+), 8 deletions(-) diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h index 1343ac57b438..4182bfbb56be 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_TAGGED_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..c21d8a0e010a 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -3928,12 +3928,24 @@ static int extent_write_cache_pages(struct address_space *mapping, range_whole = 1; scanned = 1; } - if (wbc->sync_mode == WB_SYNC_ALL) + + /* + * We don't care if we are the one who set BTRFS_INODE_TAGGED_FLUSH in + * start_delalloc_inodes(). We do the tagged writepage as long as we are + * the first one who do the filemap_flush() on this inode. + */ + if (range_whole && wbc->nr_to_write == LONG_MAX && + wbc->sync_mode == WB_SYNC_NONE && + test_and_clear_bit(BTRFS_INODE_TAGGED_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..3df3cbbe91c5 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, int 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_TAGGED_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, 1); 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, 0); 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; -- 2.19.1