On 6/5/23 14:56, 胡玮文 wrote:
On Mon, May 15, 2023 at 09:20:44AM +0800, 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.
s/introdue/introduce/
Will fix it.
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.
The posix_fadvise may change the maximum size of a file readahead.
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>
---
fs/ceph/addr.c | 40 +++++++++++++++++++++++++++++++++-------
1 file changed, 33 insertions(+), 7 deletions(-)
diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index 93fff1a7373f..4b29777c01d7 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -188,16 +188,42 @@ 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;
+ loff_t end = rreq->start + rreq->len, new_end;
+ struct ceph_netfs_request_data *priv = rreq->netfs_priv;
+ unsigned long max_len;
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;
+ if (priv) {
+ /* Readahead is disabled by posix_fadvise POSIX_FADV_RANDOM */
+ if (priv->file_ra_disabled)
+ max_pages = 0;
+ else
+ max_pages = priv->file_ra_pages;
+
+ }
+
+ /* Readahead is disabled */
+ if (!max_pages)
+ return;
- /* Now, round up the length to the next block */
- rreq->len = roundup(rreq->len, lo->stripe_unit);
+ max_len = max_pages << PAGE_SHIFT;
+
+ /*
+ * Try to expand the length forward by rounding up it to the next
An extra space between "rounding up".
Will fix it.
Apart from above two typo, LGTM.
Reviewed-by: Hu Weiwen <sehuww@xxxxxxxxxxxxxxxx>
I also tested this patch with our workload. Reading the first 16k images
from ImageNet dataset (1.69GiB) takes about 1.8Gi page cache (as
reported by `free -h'). This is expected.
For the fadvise use-case, I use `fio' to do the test:
$ fio --name=rand --size=32M --fadvise_hint=1 --ioengine=libaio --iodepth=128 --rw=randread --bs=4k --filesize=2G
after the test, page cache increased by about 35Mi, which is expected.
So if appropriate:
Tested-by: Hu Weiwen <sehuww@xxxxxxxxxxxxxxxx>
Thanks for your tests and reviewing.
However, also note random reading to a large file without fadvise still
suffers from degradation. e.g., this test:
$ fio --name=rand --size=32M --fadvise_hint=0 --ioengine=libaio --iodepth=128 --rw=randread --bs=4k --filesize=2G
will load nearly every page of the 2Gi test file into page cache,
although I only need 32Mi of them.
This is another issue since this patch just to fix blindly expanding
readahead windows, please send one following patch to fix it.
Thanks
- Xiubo
+ * 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)
--
2.40.1
