Re: [PATCH 18/25] btrfs: Use readahead_batch_length
On 12/17/20 5:42 AM, Matthew Wilcox wrote: On Thu, Dec 17, 2020 at 12:12:46PM +, 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, -- John Hubbard NVIDIA
Re: [PATCH 18/25] btrfs: Use readahead_batch_length
On Thu, Dec 17, 2020 at 12:12:46PM +, 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;
Re: [PATCH 18/25] btrfs: Use readahead_batch_length
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)
> > ---
> > 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.
Re: [PATCH 18/25] btrfs: Use readahead_batch_length
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)
---
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,
--
John Hubbard
NVIDIA
[PATCH 18/25] btrfs: Use readahead_batch_length
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)
---
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);
contiguous_readpages(pagepool, nr, contig_start, contig_end,
_cached, , _flags, _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) >>
--
2.29.2
