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

[Jan Kara <jack@suse.cz>]

On Thu 05-06-25 14:51:52, Andrew Morton wrote:
> On Thu, 5 Jun 2025 10:22:23 +0200 Jan Kara <jack@suse.cz> wrote:
> 
> > On Thu 05-06-25 13:49:35, Chi Zhiling wrote:
> > > From: Chi Zhiling <chizhiling@kylinos.cn>
> > > 
> > > 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@kylinos.cn>
> > 
> > Indeed. Thanks for catching this. Don't know how I missed that. Feel free
> > to add:
> > 
> > Reviewed-by: Jan Kara <jack@suse.cz>
> > 
> 
> 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
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR