Eric Biggers
2020-Mar-20 17:37 UTC
[Ocfs2-devel] [PATCH v9 20/25] ext4: Convert from readpages to readahead
On Fri, Mar 20, 2020 at 07:22:26AM -0700, Matthew Wilcox wrote:> From: "Matthew Wilcox (Oracle)" <willy at infradead.org> > > Use the new readahead operation in ext4 > > Signed-off-by: Matthew Wilcox (Oracle) <willy at infradead.org> > Reviewed-by: William Kucharski <william.kucharski at oracle.com> > --- > 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 <ebiggers at google.com>> + 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. - Eric
Matthew Wilcox
2020-Mar-20 17:48 UTC
[Ocfs2-devel] [PATCH v9 20/25] ext4: Convert from readpages to readahead
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)" <willy at infradead.org> > > > > Use the new readahead operation in ext4 > > > > Signed-off-by: Matthew Wilcox (Oracle) <willy at infradead.org> > > Reviewed-by: William Kucharski <william.kucharski at oracle.com> > > --- > > 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 <ebiggers at google.com> > > > + 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.