On Fri 18-09-20 10:36:35, Ritesh Harjani wrote: > 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 <[email protected]> > Suggested-by: Jan Kara <[email protected]> > Signed-off-by: Ritesh Harjani <[email protected]>
The patch looks good to me. You can add: Reviewed-by: Jan Kara <[email protected]> Honza > --- > 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 10dd470876b3..6eae17758ece 100644 > --- a/fs/ext4/inode.c > +++ b/fs/ext4/inode.c > @@ -3437,14 +3437,26 @@ 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; > -- > 2.26.2 > -- Jan Kara <[email protected]> SUSE Labs, CR
