Re: [PATCH] iomap: skip unnecessary ifs_block_is_uptodate check

[Gou Hao]

On 2025/4/9 23:30, Darrick J. Wong wrote:
> On Wed, Apr 09, 2025 at 01:29:24AM +0800, Gou Hao wrote:
> > After the first 'for' loop, the first call to
> > ifs_block_is_uptodate always evaluates to 0.
> >
> > Signed-off-by: Gou Hao <gouhao@xxxxxxxxxxxxx>
> > ---
> >   fs/iomap/buffered-io.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> > index 31553372b33a..2f52e8e61240 100644
> > --- a/fs/iomap/buffered-io.c
> > +++ b/fs/iomap/buffered-io.c
> > @@ -259,7 +259,7 @@ static void iomap_adjust_read_range(struct inode *inode, struct folio *folio,
> >   		}
> >   
> >   		/* truncate len if we find any trailing uptodate block(s) */
> > -		for ( ; i <= last; i++) {
> > +		for (i++; i <= last; i++) {
> Hmmm... prior to the loop, $i is either the first !uptodate block, or
> it's past $last.  Assuming there's no overflow (there's no combination
> of huge folios and tiny blksize that I can think of) then yeah, there's
> no point in retesting that the same block $i is uptodate since we hold
> the folio lock so nobody else could have set uptodate.
>
> Reviewed-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
>
> --D

Thank you for your review. The explanation is very clear. I will revise the

commit message and send the V2 patch.

--

thanks,

Gou Hao

> >   			if (ifs_block_is_uptodate(ifs, i)) {
> >   				plen -= (last - i + 1) * block_size;
> >   				last = i - 1;
> > --
> > 2.20.1