From 9faac62d40131521973192e46a82d5066bb42c09 Mon Sep 17 00:00:00 2001 From: Ritesh Harjani Date: Fri, 18 Sep 2020 10:36:35 +0530 Subject: [PATCH] ext4: optimize file overwrites In case if the file already has underlying blocks/extents allocated then we don't need to start a journal txn and can directly return the underlying mapping. Currently ext4_iomap_begin() is used by both DAX & DIO path. We can check if the write request is an overwrite & then directly return the mapping information. This could give a significant perf boost for multi-threaded writes specially random overwrites. On PPC64 VM with simulated pmem(DAX) device, ~10x perf improvement could be seen in random writes (overwrite). Also bcoz this optimizes away the spinlock contention during jbd2 slab cache allocation (jbd2_journal_handle). On x86 VM, ~2x perf improvement was observed. Reported-by: Dan Williams Reviewed-by: Jan Kara Signed-off-by: Ritesh Harjani Link: https://lore.kernel.org/r/88e795d8a4d5cd22165c7ebe857ba91d68d8813e.1600401668.git.riteshh@linux.ibm.com Signed-off-by: Theodore Ts'o --- fs/ext4/inode.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index f1ee0229ac12..f81f45f5db73 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -3436,14 +3436,26 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length, map.m_len = min_t(loff_t, (offset + length - 1) >> blkbits, EXT4_MAX_LOGICAL_BLOCK) - map.m_lblk + 1; - if (flags & IOMAP_WRITE) + if (flags & IOMAP_WRITE) { + /* + * We check here if the blocks are already allocated, then we + * don't need to start a journal txn and we can directly return + * the mapping information. This could boost performance + * especially in multi-threaded overwrite requests. + */ + if (offset + length <= i_size_read(inode)) { + ret = ext4_map_blocks(NULL, inode, &map, 0); + if (ret > 0 && (map.m_flags & EXT4_MAP_MAPPED)) + goto out; + } ret = ext4_iomap_alloc(inode, &map, flags); - else + } else { ret = ext4_map_blocks(NULL, inode, &map, 0); + } if (ret < 0) return ret; - +out: ext4_set_iomap(inode, iomap, &map, offset, length); return 0;