Messages in this thread | | | Date | Thu, 30 Jan 2020 00:09:39 -0800 | From | Matthew Wilcox <> | Subject | Re: [PATCH 06/12] btrfs: Convert from readpages to readahead |
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On Wed, Jan 29, 2020 at 11:46:09AM +1100, Dave Chinner wrote: > On Fri, Jan 24, 2020 at 05:35:47PM -0800, Matthew Wilcox wrote: > > From: "Matthew Wilcox (Oracle)" <willy@infradead.org> > > > > Use the new readahead operation in btrfs > > > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > > Cc: linux-btrfs@vger.kernel.org > > --- > > fs/btrfs/extent_io.c | 15 ++++----------- > > fs/btrfs/extent_io.h | 2 +- > > fs/btrfs/inode.c | 18 +++++++++--------- > > 3 files changed, 14 insertions(+), 21 deletions(-) > > > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > > index 2f4802f405a2..b1e2acbec165 100644 > > --- a/fs/btrfs/extent_io.c > > +++ b/fs/btrfs/extent_io.c > > @@ -4283,7 +4283,7 @@ int extent_writepages(struct address_space *mapping, > > return ret; > > } > > > > -int extent_readpages(struct address_space *mapping, struct list_head *pages, > > +unsigned extent_readahead(struct address_space *mapping, pgoff_t start, > > unsigned nr_pages) > > { > > struct bio *bio = NULL; > > @@ -4294,20 +4294,13 @@ int extent_readpages(struct address_space *mapping, struct list_head *pages, > > int nr = 0; > > u64 prev_em_start = (u64)-1; > > > > - while (!list_empty(pages)) { > > + while (nr_pages) { > > u64 contig_end = 0; > > > > - for (nr = 0; nr < ARRAY_SIZE(pagepool) && !list_empty(pages);) { > > - struct page *page = lru_to_page(pages); > > + for (nr = 0; nr < ARRAY_SIZE(pagepool) && nr_pages--;) { > > What is stopping nr_pages from going negative here, and then looping > forever on the outer nr_pages loop? Perhaps "while(nr_pages > 0) {" > would be better there?
Ugh, nr_pages is unsigned, so that's no good. Maybe make this a more conventional loop ...
while (nr_pages) { u64 contig_end = 0;
for (nr = 0; nr < ARRAY_SIZE(pagepool); nr++) { struct page *page = readahead_page(mapping, start++);
prefetchw(&page->flags); pagepool[nr] = page; contig_end = page_offset(page) + PAGE_SIZE - 1; if (--nr_pages == 0) break; }
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