Re: [PATCH 2/3] mm/filemap: initiate readahead even if IOCB_NOWAIT is set for the I/O

[Michal Hocko]

On Thu 31-01-19 11:15:28, Jiri Kosina wrote:
> On Thu, 31 Jan 2019, Michal Hocko wrote:
> 
> > > diff --git a/mm/filemap.c b/mm/filemap.c
> > > index 9f5e323e883e..7bcdd36e629d 100644
> > > --- a/mm/filemap.c
> > > +++ b/mm/filemap.c
> > > @@ -2075,8 +2075,6 @@ static ssize_t generic_file_buffered_read(struct kiocb *iocb,
> > >  
> > >  		page = find_get_page(mapping, index);
> > >  		if (!page) {
> > > -			if (iocb->ki_flags & IOCB_NOWAIT)
> > > -				goto would_block;
> > >  			page_cache_sync_readahead(mapping,
> > >  					ra, filp,
> > >  					index, last_index - index);
> > 
> > Maybe a stupid question but I am not really familiar with this path but
> > what exactly does prevent a sync read down page_cache_sync_readahead
> > path?
> 
> page_cache_sync_readahead() only submits the read ahead request(s), it 
> doesn't wait for it to finish.

OK, I guess my question was not precise. What does prevent taking fs
locks down the path?
-- 
Michal Hocko
SUSE Labs