Re: [PATCH 15/17] mm/filemap: Don't relock the page after calling readpage

[Matthew Wilcox <willy@infradead.org>]

On Tue, Nov 03, 2020 at 09:00:45AM +0100, Christoph Hellwig wrote:
> On Mon, Nov 02, 2020 at 06:43:10PM +0000, Matthew Wilcox (Oracle) wrote:
> > We don't need to get the page lock again; we just need to wait for
> > the I/O to finish, so use wait_on_page_locked_killable() like the
> > other callers of ->readpage.
> 
> As that isn't entirely obvious, what about adding a comment next to
> the wait_on_page_locked_killable call to document it?

The other callers of ->readpage don't document that, so not sure why
we should here?

> > +	error = wait_on_page_locked_killable(page);
> >  	if (error)
> >  		return error;
> > +	if (PageUptodate(page))
> > +		return 0;
> > +	if (!page->mapping)	/* page truncated */
> > +		return AOP_TRUNCATED_PAGE;
> > +	shrink_readahead_size_eio(&file->f_ra);
> > +	return -EIO;
> 
> You might notice a theme here, but I hate having the fast path exit
> early without a good reason, so I'd be much happier with:
> 
> 	if (!PageUptodate(page)) {
> 		if (!page->mapping)	/* page truncated */
> 			return AOP_TRUNCATED_PAGE;
> 		shrink_readahead_size_eio(&file->f_ra);
> 		return -EIO;
> 	}
> 	return 0;

I'm just not a fan of unnecessary indentation.