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Fri, 7 Feb 2020 05:08:04 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 69D0EB120; Fri, 7 Feb 2020 10:08:01 +0000 (UTC) Subject: Re: [PATCH v5 2/7] btrfs: use the page-cache for super block reading To: Johannes Thumshirn , David Sterba Cc: Josef Bacik , "linux-btrfs @ vger . kernel . org" References: <20200207072005.22867-1-johannes.thumshirn@wdc.com> <20200207072005.22867-3-johannes.thumshirn@wdc.com> From: Nikolay Borisov 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: <1905a50e-a008-0b67-ff56-080e07eaa2da@suse.com> Date: Fri, 7 Feb 2020 12:08:00 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200207072005.22867-3-johannes.thumshirn@wdc.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 7.02.20 г. 9:20 ч., Johannes Thumshirn wrote: > Super-block reading in BTRFS is done using buffer_heads. Buffer_heads have > some drawbacks, like not being able to propagate errors from the lower > layers. > > Directly use the page cache for reading the super-blocks from disk or > invalidating an on-disk super-block. We have to use the page-cache so to > avoid races between mkfs and udev. See also 6f60cbd3ae44 ("btrfs: access > superblock via pagecache in scan_one_device"). > > Signed-off-by: Johannes Thumshirn > > --- > Changes to v4: > - Remove mapping_gfp_constraint() and GFP_NOFAIL (hch) > > Changes to v3: > - Use read_cache_pages() and write_one_page() for IO (hch) > - Changed subject (David) > - Dropped Josef's R-b due to change > > Changes to v2: > - open-code kunmap() + put_page() (David) > - fix double kunmap() (David) > - don't use bi_set_op_attrs() (David) > > Changes to v1: > - move 'super_page' into for-loop in btrfs_scratch_superblocks() (Nikolay) > - switch to using pagecahce instead of alloc_pages() (Nikolay, David) > --- > fs/btrfs/disk-io.c | 76 +++++++++++++++++++++++++--------------------- > fs/btrfs/disk-io.h | 4 +-- > fs/btrfs/volumes.c | 57 ++++++++++++++++++---------------- > fs/btrfs/volumes.h | 2 -- > 4 files changed, 74 insertions(+), 65 deletions(-) > > > @@ -3355,40 +3363,38 @@ static void btrfs_end_buffer_write_sync(struct buffer_head *bh, int uptodate) > } > > int btrfs_read_dev_one_super(struct block_device *bdev, int copy_num, > - struct buffer_head **bh_ret) > + struct page **super_page) > { > - struct buffer_head *bh; > struct btrfs_super_block *super; > + struct page *page; > u64 bytenr; > + struct address_space *mapping = bdev->bd_inode->i_mapping; > > bytenr = btrfs_sb_offset(copy_num); > if (bytenr + BTRFS_SUPER_INFO_SIZE >= i_size_read(bdev->bd_inode)) > return -EINVAL; You don't use page_offset(bytenr) here but you do it in btrfs_scratch_superblocks. I'm aware that this could be omitted entirely since the sb is always aligned on a 4k. But in this case either you omit it everywhere or you use it everywhere for the sake of consistency. > > - bh = __bread(bdev, bytenr / BTRFS_BDEV_BLOCKSIZE, BTRFS_SUPER_INFO_SIZE); > - /* > - * If we fail to read from the underlying devices, as of now > - * the best option we have is to mark it EIO. > - */ > - if (!bh) > - return -EIO; > + page = read_cache_page_gfp(mapping, bytenr >> PAGE_SHIFT, GFP_NOFS); > + if (IS_ERR_OR_NULL(page)) > + return -ENOMEM; read_cache_page can return an error from ->readpage as well. Also looking at do_read_cache_page it doesn't seem like it can return a NULL pointer. > > - super = (struct btrfs_super_block *)bh->b_data; > + super = kmap(page); > if (btrfs_super_bytenr(super) != bytenr || > btrfs_super_magic(super) != BTRFS_MAGIC) { > - brelse(bh); > + kunmap(page); > + put_page(page); > return -EINVAL; > } > + kunmap(page); > > - *bh_ret = bh; > + *super_page = page; > return 0; > } > > > -struct buffer_head *btrfs_read_dev_super(struct block_device *bdev) > +int btrfs_read_dev_super(struct block_device *bdev, struct page **page) > { > - struct buffer_head *bh; > - struct buffer_head *latest = NULL; > + struct page *latest = NULL; > struct btrfs_super_block *super; > int i; > u64 transid = 0;