diff mbox series

[v4] ceph: fix blindly expanding the readahead windows

Message ID 20230509005703.155321-1-xiubli@redhat.com
State New
Headers show
Series [v4] ceph: fix blindly expanding the readahead windows | expand

Commit Message

Xiubo Li May 9, 2023, 12:57 a.m. UTC 
From: Xiubo Li <xiubli@redhat.com>

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@vger.kernel.org
Fixes: 49870056005c ("ceph: convert ceph_readpages to ceph_readahead")
URL: https://lore.kernel.org/ceph-devel/20230504082510.247-1-sehuww@mail.scut.edu.cn
URL: https://www.spinics.net/lists/ceph-users/msg76183.html
Cc: Hu Weiwen <sehuww@mail.scut.edu.cn>
Signed-off-by: Xiubo Li <xiubli@redhat.com>
---

V4:
- two small cleanup from Ilya's comments. Thanks


 fs/ceph/addr.c | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)
diff mbox series

Patch

diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index ca4dc6450887..683ba9fbd590 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -188,16 +188,30 @@  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 = min(round_up(end, lo->stripe_unit), rreq->i_size);
+	if (new_end > end && new_end <= rreq->start + max_len)
+		rreq->len = new_end - rreq->start;
+
+	/* Try to expand the start downward */
+	div_u64_rem(rreq->start, lo->stripe_unit, &blockoff);
+	if (rreq->len + blockoff <= max_len) {
+		rreq->start -= blockoff;
+		rreq->len += blockoff;
+	}
 }
 
 static bool ceph_netfs_clamp_length(struct netfs_io_subrequest *subreq)