From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Biggers Date: Fri, 20 Mar 2020 11:40:41 -0700 Subject: [Cluster-devel] [PATCH v9 20/25] ext4: Convert from readpages to readahead In-Reply-To: <20200320174848.GC4971@bombadil.infradead.org> References: <20200320142231.2402-1-willy@infradead.org> <20200320142231.2402-21-willy@infradead.org> <20200320173734.GD851@sol.localdomain> <20200320174848.GC4971@bombadil.infradead.org> Message-ID: <20200320184041.GG851@sol.localdomain> List-Id: To: cluster-devel.redhat.com MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Fri, Mar 20, 2020 at 10:48:48AM -0700, Matthew Wilcox wrote: > On Fri, Mar 20, 2020 at 10:37:34AM -0700, Eric Biggers wrote: > > On Fri, Mar 20, 2020 at 07:22:26AM -0700, Matthew Wilcox wrote: > > > From: "Matthew Wilcox (Oracle)" > > > > > > Use the new readahead operation in ext4 > > > > > > Signed-off-by: Matthew Wilcox (Oracle) > > > Reviewed-by: William Kucharski > > > --- > > > fs/ext4/ext4.h | 3 +-- > > > fs/ext4/inode.c | 21 +++++++++------------ > > > fs/ext4/readpage.c | 22 ++++++++-------------- > > > 3 files changed, 18 insertions(+), 28 deletions(-) > > > > > > > Reviewed-by: Eric Biggers > > > > > + if (rac) { > > > + page = readahead_page(rac); > > > prefetchw(&page->flags); > > > - list_del(&page->lru); > > > - if (add_to_page_cache_lru(page, mapping, page->index, > > > - readahead_gfp_mask(mapping))) > > > - goto next_page; > > > } > > > > Maybe the prefetchw(&page->flags) should be included in readahead_page()? > > Most of the callers do it. > > I did notice that a lot of callers do that. I wonder whether it (still) > helps or whether it's just cargo-cult programming. It can't possibly > have helped before because we did list_del(&page->lru) as the very next > instruction after prefetchw(), and they're in the same cacheline. It'd > be interesting to take it out and see what happens to performance. Yeah, it does look like the list_del() made the prefetchw() useless, so it should just be removed. The prefetchw() dates all the way back to mpage_readpages() being added in 2002, but even then the list_del() was immediately afterwards, and 'flags' and 'lru' were in the same cache line in 'struct page' even then (assuming at least a 32-byte cache line size), so... - Eric