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=-9.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 22BC4C169C4 for ; Mon, 11 Feb 2019 14:29:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DA2312082F for ; Mon, 11 Feb 2019 14:29:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1549895395; bh=YZk3DUqhNyrqr1pCct0f2tpY2qIIUI0UWxN8z05KQro=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=q31+0mgIi+zepuzGYFe+V9HdnUlSIPY3YfdUwpKhEFCCqttF07tSf8Un/xzMQ8nAG YQbd20DMx7UmnknVOT5W7Knl8FqAzjeeyx0nJDs46FsonBnzLzJ3AS+Se3oomO09qU NBHO6/js3nZi1XsK8ykTbJeNyBlvVIhayT0hZwgw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729126AbfBKO3x (ORCPT ); Mon, 11 Feb 2019 09:29:53 -0500 Received: from mail.kernel.org ([198.145.29.99]:35922 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730034AbfBKO3t (ORCPT ); Mon, 11 Feb 2019 09:29:49 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7220F20675; Mon, 11 Feb 2019 14:29:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1549895387; bh=YZk3DUqhNyrqr1pCct0f2tpY2qIIUI0UWxN8z05KQro=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DtRQDhjY85i30NKrNyy0HxkRbn+Qg1J3P2us643UfB5vibXZyJQPp80WOQH+me75r KUap5Loz087csa9GY5yhfQyyYWgslLlvf/PhauAgBgdf2/nAm8JN9VoBwIrgqkdvXZ bMDVv5Z+HPw43kgedwAGF4V0bG+f4U2tGwhxFCdI= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Nikolay Borisov , Ethan Lien , David Sterba , Sasha Levin Subject: [PATCH 4.20 189/352] btrfs: use tagged writepage to mitigate livelock of snapshot Date: Mon, 11 Feb 2019 15:16:56 +0100 Message-Id: <20190211141859.144055189@linuxfoundation.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190211141846.543045703@linuxfoundation.org> References: <20190211141846.543045703@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 4.20-stable review patch. If anyone has any objections, please let me know. ------------------ [ Upstream commit 3cd24c698004d2f7668e0eb9fc1f096f533c791b ] Snapshot is expected to be fast. But if there are writers steadily creating 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 omit pages dirtied after the snapshot command. This does not change the semantics regarding which data get to the snapshot, if there are pages being dirtied during the snapshotting operation. There's a sync called before snapshot is taken in old/new case, any IO in flight just after that may be in the snapshot but this depends on other system effects that might still sync the IO. 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 smaller compared to the sequential write case, since we omit only half of the pages dirtied after snapshot command. Reviewed-by: Nikolay Borisov Signed-off-by: Ethan Lien Reviewed-by: David Sterba Signed-off-by: David Sterba Signed-off-by: Sasha Levin --- fs/btrfs/btrfs_inode.h | 1 + fs/btrfs/ctree.h | 2 +- fs/btrfs/extent_io.c | 17 +++++++++++++++-- fs/btrfs/inode.c | 11 +++++++---- fs/btrfs/ioctl.c | 2 +- 5 files changed, 25 insertions(+), 8 deletions(-) diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h index a0e230b31a88..20288b49718f 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 68f322f600a0..131e90aad941 100644 --- a/fs/btrfs/ctree.h +++ b/fs/btrfs/ctree.h @@ -3141,7 +3141,7 @@ 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 d228f706ff3e..c8e886caacd7 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -3934,12 +3934,25 @@ 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. + * + * The nr_to_write == LONG_MAX is needed to make sure other flushers do + * not race in and drop the bit. + */ + 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 561bffcb56a0..965a64bde6fd 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -9988,7 +9988,7 @@ 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; @@ -10016,6 +10016,9 @@ 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); @@ -10049,7 +10052,7 @@ out: 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; @@ -10057,7 +10060,7 @@ 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; @@ -10086,7 +10089,7 @@ 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 802a628e9f7d..87f4f0f65dbb 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -777,7 +777,7 @@ 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