On 5/8/23 20:46, Ilya Dryomov wrote:
On Thu, May 4, 2023 at 1:11 PM <xiubli@xxxxxxxxxx> wrote:
From: Xiubo Li <xiubli@xxxxxxxxxx>
Blindly expanding the readahead windows will cause unneccessary
pagecache thrashing and also will introdue the network workload.
We should disable expanding the windows if the readahead is disabled
and also shouldn't expand the windows too much.
Expanding forward firstly instead of expanding backward for possible
sequential reads.
Bound `rreq->len` to the actual file size to restore the previous page
cache usage.
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 49870056005c ("ceph: convert ceph_readpages to ceph_readahead")
URL: https://lore.kernel.org/ceph-devel/20230504082510.247-1-sehuww@xxxxxxxxxxxxxxxx
URL: https://www.spinics.net/lists/ceph-users/msg76183.html
Cc: Hu Weiwen <sehuww@xxxxxxxxxxxxxxxx>
Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx>
---
V3:
- Folded Hu Weiwen's fix and bound `rreq->len` to the actual file size.
Hi Xiubo,
This looks much better! Just a couple of nits:
fs/ceph/addr.c | 28 ++++++++++++++++++++++------
1 file changed, 22 insertions(+), 6 deletions(-)
diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index ca4dc6450887..357d9d28f202 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -188,16 +188,32 @@ static void ceph_netfs_expand_readahead(struct netfs_io_request *rreq)
struct inode *inode = rreq->inode;
struct ceph_inode_info *ci = ceph_inode(inode);
struct ceph_file_layout *lo = &ci->i_layout;
+ unsigned long max_pages = inode->i_sb->s_bdi->ra_pages;
+ unsigned long max_len = max_pages << PAGE_SHIFT;
+ loff_t end = rreq->start + rreq->len, new_end;
u32 blockoff;
u64 blockno;
- /* Expand the start downward */
- blockno = div_u64_rem(rreq->start, lo->stripe_unit, &blockoff);
- rreq->start = blockno * lo->stripe_unit;
- rreq->len += blockoff;
+ /* Readahead is disabled */
+ if (!max_pages)
+ return;
- /* Now, round up the length to the next block */
- rreq->len = roundup(rreq->len, lo->stripe_unit);
+ /*
+ * Try to expand the length forward by rounding up it to the next
+ * block, but do not exceed the file size, unless the original
+ * request already exceeds it.
+ */
+ new_end = round_up(end, lo->stripe_unit);
+ new_end = min(new_end, rreq->i_size);
This can be done on single line:
new_end = min(round_up(end, lo->stripe_unit), rreq->i_size);
Sure, will fix it.
+ if (new_end > end && new_end <= rreq->start + max_len)
+ rreq->len = new_end - rreq->start;
+
+ /* Try to expand the start downward */
+ blockno = div_u64_rem(rreq->start, lo->stripe_unit, &blockoff);
+ if (rreq->len + blockoff <= max_len) {
+ rreq->start = blockno * lo->stripe_unit;
Can this be written as:
rreq->start -= blockoff;
It seems like it would be easier to read and probably cheaper to
compute too.
Yeah, this looks much easier to understand.
Thanks
- Xiubo
Thanks,
Ilya
