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Thu, 1 Nov 2018 17:00:09 -0400 Received: from mx2.suse.de ([195.135.220.15]:44150 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728085AbeKAVAI (ORCPT ); Thu, 1 Nov 2018 17:00:08 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id C536CADCE; Thu, 1 Nov 2018 11:57:28 +0000 (UTC) Subject: Re: [PATCH] btrfs: use tagged writepage to mitigate livelock of snapshot To: Ethan Lien , linux-btrfs@vger.kernel.org References: <20181101064903.11638-1-ethanlien@synology.com> From: Nikolay Borisov Openpgp: preference=signencrypt Autocrypt: addr=nborisov@suse.com; prefer-encrypt=mutual; keydata= xsFNBFiKBz4BEADNHZmqwhuN6EAzXj9SpPpH/nSSP8YgfwoOqwrP+JR4pIqRK0AWWeWCSwmZ T7g+RbfPFlmQp+EwFWOtABXlKC54zgSf+uulGwx5JAUFVUIRBmnHOYi/lUiE0yhpnb1KCA7f u/W+DkwGerXqhhe9TvQoGwgCKNfzFPZoM+gZrm+kWv03QLUCr210n4cwaCPJ0Nr9Z3c582xc bCUVbsjt7BN0CFa2BByulrx5xD9sDAYIqfLCcZetAqsTRGxM7LD0kh5WlKzOeAXj5r8DOrU2 GdZS33uKZI/kZJZVytSmZpswDsKhnGzRN1BANGP8sC+WD4eRXajOmNh2HL4P+meO1TlM3GLl EQd2shHFY0qjEo7wxKZI1RyZZ5AgJnSmehrPCyuIyVY210CbMaIKHUIsTqRgY5GaNME24w7h TyyVCy2qAM8fLJ4Vw5bycM/u5xfWm7gyTb9V1TkZ3o1MTrEsrcqFiRrBY94Rs0oQkZvunqia c+NprYSaOG1Cta14o94eMH271Kka/reEwSZkC7T+o9hZ4zi2CcLcY0DXj0qdId7vUKSJjEep c++s8ncFekh1MPhkOgNj8pk17OAESanmDwksmzh1j12lgA5lTFPrJeRNu6/isC2zyZhTwMWs k3LkcTa8ZXxh0RfWAqgx/ogKPk4ZxOXQEZetkEyTFghbRH2BIwARAQABzSJOaWtvbGF5IEJv cmlzb3YgPG5ib3Jpc292QHN1c2UuZGU+wsF4BBMBAgAiBQJYijkSAhsDBgsJCAcDAgYVCAIJ CgsEFgIDAQIeAQIXgAAKCRBxvoJG5T8oV/B6D/9a8EcRPdHg8uLEPywuJR8URwXzkofT5bZE IfGF0Z+Lt2ADe+nLOXrwKsamhweUFAvwEUxxnndovRLPOpWerTOAl47lxad08080jXnGfYFS Dc+ew7C3SFI4tFFHln8Y22Q9075saZ2yQS1ywJy+TFPADIprAZXnPbbbNbGtJLoq0LTiESnD w/SUC6sfikYwGRS94Dc9qO4nWyEvBK3Ql8NkoY0Sjky3B0vL572Gq0ytILDDGYuZVo4alUs8 LeXS5ukoZIw1QYXVstDJQnYjFxYgoQ5uGVi4t7FsFM/6ykYDzbIPNOx49Rbh9W4uKsLVhTzG BDTzdvX4ARl9La2kCQIjjWRg+XGuBM5rxT/NaTS78PXjhqWNYlGc5OhO0l8e5DIS2tXwYMDY LuHYNkkpMFksBslldvNttSNei7xr5VwjVqW4vASk2Aak5AleXZS+xIq2FADPS/XSgIaepyTV tkfnyreep1pk09cjfXY4A7qpEFwazCRZg9LLvYVc2M2eFQHDMtXsH59nOMstXx2OtNMcx5p8 0a5FHXE/HoXz3p9bD0uIUq6p04VYOHsMasHqHPbsMAq9V2OCytJQPWwe46bBjYZCOwG0+x58 fBFreP/NiJNeTQPOa6FoxLOLXMuVtpbcXIqKQDoEte9aMpoj9L24f60G4q+pL/54ql2VRscK d87BTQRYigc+ARAAyJSq9EFk28++SLfg791xOh28tLI6Yr8wwEOvM3wKeTfTZd+caVb9gBBy wxYhIopKlK1zq2YP7ZjTP1aPJGoWvcQZ8fVFdK/1nW+Z8/NTjaOx1mfrrtTGtFxVBdSCgqBB jHTnlDYV1R5plJqK+ggEP1a0mr/rpQ9dFGvgf/5jkVpRnH6BY0aYFPprRL8ZCcdv2DeeicOO YMobD5g7g/poQzHLLeT0+y1qiLIFefNABLN06Lf0GBZC5l8hCM3Rpb4ObyQ4B9PmL/KTn2FV Xq/c0scGMdXD2QeWLePC+yLMhf1fZby1vVJ59pXGq+o7XXfYA7xX0JsTUNxVPx/MgK8aLjYW hX+TRA4bCr4uYt/S3ThDRywSX6Hr1lyp4FJBwgyb8iv42it8KvoeOsHqVbuCIGRCXqGGiaeX Wa0M/oxN1vJjMSIEVzBAPi16tztL/wQtFHJtZAdCnuzFAz8ue6GzvsyBj97pzkBVacwp3/Mw qbiu7sDz7yB0d7J2tFBJYNpVt/Lce6nQhrvon0VqiWeMHxgtQ4k92Eja9u80JDaKnHDdjdwq FUikZirB28UiLPQV6PvCckgIiukmz/5ctAfKpyYRGfez+JbAGl6iCvHYt/wAZ7Oqe/3Cirs5 KhaXBcMmJR1qo8QH8eYZ+qhFE3bSPH446+5oEw8A9v5oonKV7zMAEQEAAcLBXwQYAQIACQUC WIoHPgIbDAAKCRBxvoJG5T8oV1pyD/4zdXdOL0lhkSIjJWGqz7Idvo0wjVHSSQCbOwZDWNTN JBTP0BUxHpPu/Z8gRNNP9/k6i63T4eL1xjy4umTwJaej1X15H8Hsh+zakADyWHadbjcUXCkg OJK4NsfqhMuaIYIHbToi9K5pAKnV953xTrK6oYVyd/Rmkmb+wgsbYQJ0Ur1Ficwhp6qU1CaJ mJwFjaWaVgUERoxcejL4ruds66LM9Z1Qqgoer62ZneID6ovmzpCWbi2sfbz98+kW46aA/w8r 7sulgs1KXWhBSv5aWqKU8C4twKjlV2XsztUUsyrjHFj91j31pnHRklBgXHTD/pSRsN0UvM26 lPs0g3ryVlG5wiZ9+JbI3sKMfbdfdOeLxtL25ujs443rw1s/PVghphoeadVAKMPINeRCgoJH zZV/2Z/myWPRWWl/79amy/9MfxffZqO9rfugRBORY0ywPHLDdo9Kmzoxoxp9w3uTrTLZaT9M KIuxEcV8wcVjr+Wr9zRl06waOCkgrQbTPp631hToxo+4rA1jiQF2M80HAet65ytBVR2pFGZF zGYYLqiG+mpUZ+FPjxk9kpkRYz61mTLSY7tuFljExfJWMGfgSg1OxfLV631jV1TcdUnx+h3l Sqs2vMhAVt14zT8mpIuu2VNxcontxgVr1kzYA/tQg32fVRbGr449j1gw57BV9i0vww== Message-ID: <857dc4ea-245b-623e-a734-b247d5b54149@suse.com> Date: Thu, 1 Nov 2018 13:57:26 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20181101064903.11638-1-ethanlien@synology.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 1.11.18 г. 8:49 ч., Ethan Lien wrote: > 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)) Actually this check can be simplified to: range_whole && test_and_clear_bit. filemap_flush triggers range_whole = 1 and then you care about TAGGED_FLUSH (or w/e it's going to be named) to be set. The nr_to_write && syncmode just make it a tad more difficult to reason about the code. > + 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; > >