Re: [PATCH] ext4: remove unnecessary ext4_inode_datasync_dirty in read path

Dave Chinner
2021-11-03T00:28:49Z

On Tue, Nov 02, 2021 at 10:42:58AM +0800, Zhongwei Cai wrote:
> ext4_inode_datasync_dirty will call read_lock(&journal->j_state_lock) in
> journal mode, which is unnecessary in read path (As far as I know, the
> IOMAP_F_DIRTY flag set in the if branch is only used in write path,
> making it unnecessary in read path. Please correct me if I'm wrong).

IOMAP_F_DIRTY isn't conditional on the type of lookup being done. If
the inode is dirty in a way that O_DSYNC would require it to be
flushed to make the data stable, iomap should be told that it is
dirty, even on read lookups...

e.g. iomap_swapfile_activate() uses IOMAP_REPORT as the flags for
extent mapping iteration passed to iomap_swapfile_iter(). THis then
checks:

/* No uncommitted metadata or shared blocks. */
if (iomap->flags & IOMAP_F_DIRTY)
return iomap_swapfile_fail(isi, "is not committed");

IOWs, we expect the IOMAP_F_DIRTY flag to be set on all types of
iomap mapping calls if the inode is dirty, not just IOMAP_WRITE
calls.