Re: [PATCH 1/2] mm/readahead: stop readahead loop if memcg charge fails

From: Matthew Wilcox <willy@infradead.org>
To: Jan Kara <jack@suse.cz>
Cc: Liu Shixin <liushixin2@huawei.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Christian Brauner <brauner@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: [PATCH 1/2] mm/readahead: stop readahead loop if memcg charge fails
Date: Thu, 1 Feb 2024 13:53:54 +0000	[thread overview]
Message-ID: <ZbuickwNyxExIVzC@casper.infradead.org> (raw)
In-Reply-To: <20240201135231.tgnn7cnlmtqh5n4f@quack3>

On Thu, Feb 01, 2024 at 02:52:31PM +0100, Jan Kara wrote:
> On Thu 01-02-24 13:47:03, Matthew Wilcox wrote:
> > On Thu, Feb 01, 2024 at 06:08:34PM +0800, Liu Shixin wrote:
> > > @@ -247,9 +248,12 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
> > >  		folio = filemap_alloc_folio(gfp_mask, 0);
> > >  		if (!folio)
> > >  			break;
> > > -		if (filemap_add_folio(mapping, folio, index + i,
> > > -					gfp_mask) < 0) {
> > > +
> > > +		ret = filemap_add_folio(mapping, folio, index + i, gfp_mask);
> > > +		if (ret < 0) {
> > >  			folio_put(folio);
> > > +			if (ret == -ENOMEM)
> > > +				break;
> > 
> > No, that's too early.  You've still got a batch of pages which were
> > successfully added; you have to read them.  You were only off by one
> > line though ;-)
> 
> There's a read_pages() call just outside of the loop so this break is
> actually fine AFAICT.

Oh, good point!  I withdraw my criticism.