Re: [PATCH] iomap: avoid unnecessary ifs_set_range_uptodate() with locks

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Jul 02, 2025 at 08:09:12PM +0800, Jinliang Zheng wrote:
> On Tue, 1 Jul 2025 11:47:37 -0700, djwong@kernel.org wrote:
> > On Tue, Jul 03, 2025 at 10:48:47PM +0800, alexjlzheng@gmail.com wrote:
> > > From: Jinliang Zheng <alexjlzheng@tencent.com>
> > > 
> > > In the buffer write path, iomap_set_range_uptodate() is called every
> > > time iomap_end_write() is called. But if folio_test_uptodate() holds, we
> > > know that all blocks in this folio are already in the uptodate state, so
> > > there is no need to go deep into the critical section of state_lock to
> > > execute bitmap_set().
> > > 
> > > Although state_lock may not have significant lock contention due to
> > > folio lock, this patch at least reduces the number of instructions.
> > > 
> > > Signed-off-by: Jinliang Zheng <alexjlzheng@tencent.com>
> > > ---
> > >  fs/iomap/buffered-io.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> > > index 3729391a18f3..fb4519158f3a 100644
> > > --- a/fs/iomap/buffered-io.c
> > > +++ b/fs/iomap/buffered-io.c
> > > @@ -71,6 +71,9 @@ static void iomap_set_range_uptodate(struct folio *folio, size_t off,
> > >  	unsigned long flags;
> > >  	bool uptodate = true;
> > >  
> > > +	if (folio_test_uptodate(folio))
> > > +		return;
> > 
> > Looks fine, but how exhaustively have you tested this with heavy IO
> > workloads?  I /think/ it's the case that folios always creep towards
> > ifs_is_fully_uptodate() == true state and once they've gotten there
> > never go back.  But folio state bugs are tricky to detect once they've
> > crept in.
> 
> I tested fio, ltp and xfstests combined for about 30 hours. The command
> used for fio test is:
> 
>   fio --name=4k-rw \
>     --filename=/data2/testfile \
>     --size=1G \
>     --bs=4096 \
>     --ioengine=libaio \
>     --iodepth=32 \
>     --rw=randrw \
>     --direct=0 \
>     --buffered=1 \
>     --numjobs=16 \
>     --runtime=60 \
>     --time_based \
>     --group_reporting
> 
> ltp and xfstests showed no noticeable errors caused by this patch.

<nod> I think this fine then...
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> 
> thanks,
> Jinliang Zheng. :)
> 
> > 
> > --D
> > 
> > > +
> > >  	if (ifs) {
> > >  		spin_lock_irqsave(&ifs->state_lock, flags);
> > >  		uptodate = ifs_set_range_uptodate(folio, ifs, off, len);
> > > -- 
> > > 2.49.0
> > > 
> > > 
>