This patch series makes inode cluster size a tunnable parameter in mkfs.xfs when sparse allocation is enabled, and also makes xfs use inode cluster size directly from the superblock read in rather than recalculate itself and verify. Under extreme fragmentation situations, even inode sparse allocation may fail with current default inode cluster size i.e. 8192 bytes. Such situations may come from the PUNCH_HOLE fallocation which is used by some applications, for example MySQL innodb page compression. With xfs of 4K blocksize, MySQL may write out 16K buffer with direct I/O(which immediately triggers block allocation) then try to compress the 16K buffer to <4K. If the compression succeeds, MySQL will punch out the latter 12K, leave only the first 4K allocated: after write 16k buffer: OOOO after punch latter 12K: OXXX where O means page with block allocated, X means page without. Such feature saves disk space(the 12K freed by punching can be used by others), but also makes the filesystem much more fragmented. Considering xfs has no automatic defragmentation mechanism, in the most extreme cases, there will be only 1-3 physically continuous blocks finally avaliable. For data block allocation, such fragmentation is not a problem, as physical continuation is not always required. But inode chunk allocation requires so. Even for sparse allocation, physical continuation has also to be guaranteed in a way. Currently this value is calculated from a scaled inode cluster size. In xfs, inodes are manipulated(e.g. read in, logged, written back) in cluster, and the size of that cluster is just the inode cluster size. Sparse allocation unit currently is calculated from that: (inode size / MIN_INODE_SIZE) * inode cluster size -> sparse allocation aligmnet -> sparse allocation unit For example, under default mkfs configuration(i.e. crc and sparse allocation enabled, 4K blocksize), inode size is 512 bytes(2 times of MIN_INODE_SIZE=256 bytes), then sparse allocation unit will be 2 * current inode cluster size(8192 bytes) = 16384 bytes, that is 4 blocks. As we mentioned above, under extreme fragmentation, the filesystem may be full of 1-3 physically continuous blocks but can never find one of 4, so even sparese allocation will also fail. If we know application will easily create such fragmentation, then we had better have a way to loose sparse allocation requirement manually. This patch series achieves that by making the source of sparse allocation unit, inode cluster size a tunnable parameter. When sparse allocation enabled, make that size tunnable in mkfs. As xfs itself currently recalculate and verify related value, change xfs behavior to directly using the value provided by superblock read in. Tianxiang Peng (2): xfs: calculate cluster_size_raw from sb when sparse alloc enabled mkfs: make cluster size tunnable when sparse alloc enabled fs/xfs/libxfs/xfs_ialloc.c | 35 ++++++++++++++++++++++------------- fs/xfs/xfs_mount.c | 12 ++++++------ mkfs/xfs_mkfs.c | 34 +++++++++++++++++++++++++++++----- 3 files changed, 57 insertions(+), 24 deletions(-) -- 2.43.5
