| Message ID | 20201216182335.27227-19-willy@infradead.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Page folios | expand |
On 12/16/20 10:23 AM, Matthew Wilcox (Oracle) wrote: > Implement readahead_batch_length() to determine the number of bytes in > the current batch of readahead pages and use it in btrfs. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > --- > fs/btrfs/extent_io.c | 6 ++---- > include/linux/pagemap.h | 9 +++++++++ > 2 files changed, 11 insertions(+), 4 deletions(-) > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > index 6e3b72e63e42..42936a83a91b 100644 > --- a/fs/btrfs/extent_io.c > +++ b/fs/btrfs/extent_io.c > @@ -4436,10 +4436,8 @@ void extent_readahead(struct readahead_control *rac) > int nr; > > while ((nr = readahead_page_batch(rac, pagepool))) { > - u64 contig_start = page_offset(pagepool[0]); > - u64 contig_end = page_offset(pagepool[nr - 1]) + PAGE_SIZE - 1; > - > - ASSERT(contig_start + nr * PAGE_SIZE - 1 == contig_end); > + u64 contig_start = readahead_pos(rac); > + u64 contig_end = contig_start + readahead_batch_length(rac); Something in this tiny change is breaking btrfs: it hangs my Fedora 33 test system (which changed over to btrfs) on boot. I haven't quite figured out what's really wrong, but git bisect lands here, *and* turning the whole extent_readahead() function into a no-op (on top of the whole series) allows everything to work once again. Sorry for not actually solving the root cause, but I figured you'd be able to jump straight to the answer, with the above information, so I'm sending it out early. thanks,
On Thu, Dec 17, 2020 at 01:15:10AM -0800, John Hubbard wrote: > On 12/16/20 10:23 AM, Matthew Wilcox (Oracle) wrote: > > Implement readahead_batch_length() to determine the number of bytes in > > the current batch of readahead pages and use it in btrfs. > > > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > > --- > > fs/btrfs/extent_io.c | 6 ++---- > > include/linux/pagemap.h | 9 +++++++++ > > 2 files changed, 11 insertions(+), 4 deletions(-) > > > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > > index 6e3b72e63e42..42936a83a91b 100644 > > --- a/fs/btrfs/extent_io.c > > +++ b/fs/btrfs/extent_io.c > > @@ -4436,10 +4436,8 @@ void extent_readahead(struct readahead_control *rac) > > int nr; > > while ((nr = readahead_page_batch(rac, pagepool))) { > > - u64 contig_start = page_offset(pagepool[0]); > > - u64 contig_end = page_offset(pagepool[nr - 1]) + PAGE_SIZE - 1; > > - > > - ASSERT(contig_start + nr * PAGE_SIZE - 1 == contig_end); > > + u64 contig_start = readahead_pos(rac); > > + u64 contig_end = contig_start + readahead_batch_length(rac); > > Something in this tiny change is breaking btrfs: it hangs my Fedora 33 test > system (which changed over to btrfs) on boot. I haven't quite figured out > what's really wrong, but git bisect lands here, *and* turning the whole > extent_readahead() function into a no-op (on top of the whole series) > allows everything to work once again. > > Sorry for not actually solving the root cause, but I figured you'd be able > to jump straight to the answer, with the above information, so I'm sending > it out early. ehh ... probably an off-by-one. Does subtracting 1 from contig_end fix it? I'll spool up a test VM shortly and try it out.
On Thu, Dec 17, 2020 at 12:12:46PM +0000, Matthew Wilcox wrote: > ehh ... probably an off-by-one. Does subtracting 1 from contig_end fix it? > I'll spool up a test VM shortly and try it out. Yes, this fixed it: - u64 contig_end = contig_start + readahead_batch_length(rac); + u64 contig_end = contig_start + readahead_batch_length(rac) - 1;
On 12/17/20 5:42 AM, Matthew Wilcox wrote: > On Thu, Dec 17, 2020 at 12:12:46PM +0000, Matthew Wilcox wrote: >> ehh ... probably an off-by-one. Does subtracting 1 from contig_end fix it? >> I'll spool up a test VM shortly and try it out. > > Yes, this fixed it: > > - u64 contig_end = contig_start + readahead_batch_length(rac); > + u64 contig_end = contig_start + readahead_batch_length(rac) - 1; > Yes, confirmed on my end, too. thanks,
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 6e3b72e63e42..42936a83a91b 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -4436,10 +4436,8 @@ void extent_readahead(struct readahead_control *rac) int nr; while ((nr = readahead_page_batch(rac, pagepool))) { - u64 contig_start = page_offset(pagepool[0]); - u64 contig_end = page_offset(pagepool[nr - 1]) + PAGE_SIZE - 1; - - ASSERT(contig_start + nr * PAGE_SIZE - 1 == contig_end); + u64 contig_start = readahead_pos(rac); + u64 contig_end = contig_start + readahead_batch_length(rac); contiguous_readpages(pagepool, nr, contig_start, contig_end, &em_cached, &bio, &bio_flags, &prev_em_start); diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 630a0a589073..81ff21289722 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -1048,6 +1048,15 @@ static inline unsigned int readahead_count(struct readahead_control *rac) return rac->_nr_pages; } +/** + * readahead_batch_length - The number of bytes in the current batch. + * @rac: The readahead request. + */ +static inline loff_t readahead_batch_length(struct readahead_control *rac) +{ + return rac->_batch_count * PAGE_SIZE; +} + static inline unsigned long dir_pages(struct inode *inode) { return (unsigned long)(inode->i_size + PAGE_SIZE - 1) >>
Implement readahead_batch_length() to determine the number of bytes in the current batch of readahead pages and use it in btrfs. Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> --- fs/btrfs/extent_io.c | 6 ++---- include/linux/pagemap.h | 9 +++++++++ 2 files changed, 11 insertions(+), 4 deletions(-)