From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cantor2.suse.de ([195.135.220.15]:60228 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751133AbbFKPZT (ORCPT ); Thu, 11 Jun 2015 11:25:19 -0400 Received: from relay2.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 51B23AD27 for ; Thu, 11 Jun 2015 15:25:18 +0000 (UTC) Message-ID: <5579A85C.2040301@suse.com> Date: Thu, 11 Jun 2015 11:25:16 -0400 From: Jeff Mahoney MIME-Version: 1.0 To: linux-btrfs@vger.kernel.org Subject: Re: [PATCH 1/4] btrfs: skip superblocks during discard References: <1434036062-21597-1-git-send-email-jeffm@suse.com> <1434036062-21597-2-git-send-email-jeffm@suse.com> In-Reply-To: <1434036062-21597-2-git-send-email-jeffm@suse.com> Content-Type: text/plain; charset=windows-1252 Sender: linux-btrfs-owner@vger.kernel.org List-ID: -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 6/11/15 11:20 AM, jeffm@suse.com wrote: > From: Jeff Mahoney > > Btrfs doesn't track superblocks with extent records so there is > nothing persistent on-disk to indicate that those blocks are in > use. We track the superblocks in memory to ensure they don't get > used by removing them from the free space cache when we load a > block group from disk. Prior to 47ab2a6c6a (Btrfs: remove empty > block groups automatically), that was fine since the block group > would never be reclaimed so the superblock was always safe. Once > we started removing the empty block groups, we were protected by > the fact that discards weren't being properly issued for unused > space either via FITRIM or -odiscard. The block groups were still > being released, but the blocks remained on disk. > > In order to properly discard unused block groups, we need to filter > out the superblocks from the discard range. Superblocks are > located at fixed locations on each device, so it makes sense to > filter them out in btrfs_issue_discard, which is used by both > -odiscard and FITRIM. > > Signed-off-by: Jeff Mahoney --- > fs/btrfs/extent-tree.c | 50 > ++++++++++++++++++++++++++++++++++++++++++++------ 1 file changed, > 44 insertions(+), 6 deletions(-) > > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index > 0ec3acd..75d0226 100644 --- a/fs/btrfs/extent-tree.c +++ > b/fs/btrfs/extent-tree.c @@ -1884,10 +1884,47 @@ static int > remove_extent_backref(struct btrfs_trans_handle *trans, return > ret; } > > -static int btrfs_issue_discard(struct block_device *bdev, - u64 > start, u64 len) +#define in_range(b, first, len) ((b) >= (first) && > (b) < (first) + (len)) +static int btrfs_issue_discard(struct > block_device *bdev, u64 start, u64 len, + u64 > *discarded_bytes) { - return blkdev_issue_discard(bdev, start >> 9, > len >> 9, GFP_NOFS, 0); + u64 skipped = 0; + u64 bytes_left = len; > + int ret = 0 , j; + + *discarded_bytes = 0; + + /* Skip any > superblocks on this device. */ + for (j = 0; j < > BTRFS_SUPER_MIRROR_MAX; j++) { + u64 sb_offset = > btrfs_sb_offset(j); + u64 size = sb_offset - start; + + if > (!in_range(sb_offset, start, bytes_left)) + continue; + + if > (size) { + ret = blkdev_issue_discard(bdev, start >> 9, size >> > 9, + GFP_NOFS, 0); + if (!ret) + *discarded_bytes += > size; + else if (ret != -EOPNOTSUPP) + return ret; + } + + > start = sb_offset + BTRFS_SUPER_INFO_SIZE; + if (start > len) + > start = len; + bytes_left = len - start; + skipped += > BTRFS_SUPER_INFO_SIZE; Whoops. This is an unused artifact from an earlier version. - -Jeff > + } + + if (bytes_left) { + ret = blkdev_issue_discard(bdev, start > >> 9, bytes_left >> 9, + GFP_NOFS, 0); + if (!ret) + > *discarded_bytes += bytes_left; + } + return ret; } > > int btrfs_discard_extent(struct btrfs_root *root, u64 bytenr, @@ > -1906,16 +1943,17 @@ int btrfs_discard_extent(struct btrfs_root > *root, u64 bytenr, struct btrfs_bio_stripe *stripe = > bbio->stripes; int i; > > - for (i = 0; i < bbio->num_stripes; i++, stripe++) { + u64 > bytes; + if (!stripe->dev->can_discard) continue; > > ret = btrfs_issue_discard(stripe->dev->bdev, stripe->physical, - > stripe->length); + stripe->length, &bytes); if (!ret) - > discarded_bytes += stripe->length; + discarded_bytes += bytes; > else if (ret != -EOPNOTSUPP) break; /* Logic errors or -ENOMEM, or > -EIO but I don't know how that could happen JDM */ > > - -- Jeff Mahoney SUSE Labs -----BEGIN PGP SIGNATURE----- Version: GnuPG/MacGPG2 v2.0.19 (Darwin) iQIcBAEBAgAGBQJVeahbAAoJEB57S2MheeWyA3YP/00sK18TqJi6ohu0l18otsd2 vG2lAtPUDT6f4dFM1GvO4PYLssuwm0Vy98qFYO30lvcHbdbajhsGd1qk+IzEq3Dr +Qxze9lIrX8267nRE3aqu1I8/y2Gn5Wcy5Xr6fwhN0g+m5J+fWZHy1mfTvqbNt+M U7Cg4hgvTFDcuV5adrg3JoQ3W/w6IvgIid27oNZ0MJMaK4f2jcLfmhGVCTcCnydp 7fEUsMow2firGJew7161ORYkYjTn76JW2HXB8ETOgWUcMpZon1KWduVXOTD0r9sk UrfMJ8dLw6334T265gmQrBXvb3yOBLbyRYuksUFhXFUo1/xDSQMLGMBrkEf6T/Vo mwnXVw5hnPM41vZiJ4Pc56vg1Yy4JGMXs28XEyHrj7gQWo3b1jRw0YhosZE/TR5+ BsJb4KqBTPor/upPLmDwIOYU4Ia+GZ5V2k1jYsE9qs6khHXlX9is8WHeB/fMzfCe zkZEl8YI3ek50wXcqBk+QHFj8LT89Eyq59O3iaCFceIhvjO87ldRDBtTtBR34ogf mZphx9UzVTcY31wftDYKMMi2Xs+8BZgXq7H7IXc2muugFlK9AGsMv4iXPbVkmUmE T4pS2vKqCwfkW9bGf7ufQaOpVgwzQjDkC/Ngtybl8sULroOjI3lm6p+2/jMuqyYd twV2FaYAJAI/tiQkTken =1g/b -----END PGP SIGNATURE-----