Re: [PATCH] readahead: fix return value of page_cache_next_miss() when no hole is found

[Chi Zhiling]

On 2025/6/6 18:54, Jan Kara wrote:
> On Thu 05-06-25 14:51:52, Andrew Morton wrote:
> > On Thu, 5 Jun 2025 10:22:23 +0200 Jan Kara <jack@xxxxxxx> wrote:
> >
> > > On Thu 05-06-25 13:49:35, Chi Zhiling wrote:
> > > > From: Chi Zhiling <chizhiling@xxxxxxxxxx>
> > > >
> > > > max_scan in page_cache_next_miss always decreases to zero when no hole
> > > > is found, causing the return value to be index + 0.
> > > >
> > > > Fix this by preserving the max_scan value throughout the loop.
> > > >
> > > > Fixes: 901a269ff3d5 ("filemap: fix page_cache_next_miss() when no hole found")
> > > > Signed-off-by: Chi Zhiling <chizhiling@xxxxxxxxxx>
> > >
> > > Indeed. Thanks for catching this. Don't know how I missed that. Feel free
> > > to add:
> > >
> > > Reviewed-by: Jan Kara <jack@xxxxxxx>

Thanks

> > >
> >
> > Thanks.  It's a simple patch - do we expect it to have significant
> > runtime effects?
>
> I'm not sure if Chi Zhiling observed some practical effects. From what I
> know and have seen in the past, wrong responses from page_cache_next_miss()
> can lead to readahead window reduction and thus reduced read speeds.
>
> 								Honza

TBH, in my simple sequential reading test, I did not see any significant 
speed improvement.