On 11/10/23 10:40, Gregory Farnum wrote:
[ Moving from ceph-devel@vger to dev@ceph ]
Do we need to change the protocol so you can provide a limit on the
number of extents when you send a sparse read op?
I rather suspect the workloads generating this are the worst case
scenario and that we may want server-side limits in any case
AFAIK, for this we need to change protocol.
For random writes for a large file, from my test the worse case it could
return thousands of extents for sparse read.
Thanks
- Xiubo
On Mon, Nov 6, 2023 at 5:02 AM Xiubo Li <xiubli@xxxxxxxxxx> wrote:
On 11/6/23 20:32, Ilya Dryomov wrote:
On Mon, Nov 6, 2023 at 1:15 PM Xiubo Li <xiubli@xxxxxxxxxx> wrote:
On 11/6/23 19:38, Ilya Dryomov wrote:
On Mon, Nov 6, 2023 at 1:14 AM Xiubo Li <xiubli@xxxxxxxxxx> wrote:
On 11/3/23 18:07, Ilya Dryomov wrote:
On Fri, Nov 3, 2023 at 4:41 AM <xiubli@xxxxxxxxxx> wrote:
From: Xiubo Li <xiubli@xxxxxxxxxx>
There is no any limit for the extent array size and it's possible
that when reading with a large size contents. Else the messager
will fail by reseting the connection and keeps resending the inflight
IOs.
URL: https://tracker.ceph.com/issues/62081
Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx>
---
net/ceph/osd_client.c | 12 ------------
1 file changed, 12 deletions(-)
diff --git a/net/ceph/osd_client.c b/net/ceph/osd_client.c
index 7af35106acaf..177a1d92c517 100644
--- a/net/ceph/osd_client.c
+++ b/net/ceph/osd_client.c
@@ -5850,8 +5850,6 @@ static inline void convert_extent_map(struct ceph_sparse_read *sr)
}
#endif
-#define MAX_EXTENTS 4096
-
static int osd_sparse_read(struct ceph_connection *con,
struct ceph_msg_data_cursor *cursor,
char **pbuf)
@@ -5882,16 +5880,6 @@ static int osd_sparse_read(struct ceph_connection *con,
if (count > 0) {
if (!sr->sr_extent || count > sr->sr_ext_len) {
- /*
- * Apply a hard cap to the number of extents.
- * If we have more, assume something is wrong.
- */
- if (count > MAX_EXTENTS) {
- dout("%s: OSD returned 0x%x extents in a single reply!\n",
- __func__, count);
- return -EREMOTEIO;
- }
-
/* no extent array provided, or too short */
kfree(sr->sr_extent);
sr->sr_extent = kmalloc_array(count,
--
2.39.1
Hi Xiubo,
As noted in the tracker ticket, there are many "sanity" limits like
that in the messenger and other parts of the kernel client. First,
let's change that dout to pr_warn_ratelimited so that it's immediately
clear what is going on.
Sounds good to me.
Then, if the limit actually gets hit, let's
dig into why and see if it can be increased rather than just removed.
The test result in https://tracker.ceph.com/issues/62081#note-16 is that I just changed the 'len' to 5000 in ceph PR https://github.com/ceph/ceph/pull/54301 to emulate a random writes to a file and then tries to read with a large size:
[ RUN ] LibRadosIoPP.SparseReadExtentArrayOpPP
extents array size : 4297
For the 'extents array size' it could reach up to a very large number, then what it should be ? Any idea ?
Hi Xiubo,
I don't think it can be a very large number in practice.
CephFS uses sparse reads only in the fscrypt case, right?
Yeah, it is.
With
fscrypt, sub-4K writes to the object store aren't possible, right?
Yeah.
If the answer to both is yes, then the maximum number of extents
would be
64M (CEPH_MSG_MAX_DATA_LEN) / 4K = 16384
even if the object store does tracking at byte granularity.
So yeah, just for the fscrypt case if we set the max extent number to
16384 it should be fine. But the sparse read could also be enabled in
non-fscrypt case.
Ah, I see that it's also exposed as a mount option. If we expect
people to use it, then dropping MAX_EXTENTS altogether might be the
best approach after all -- it doesn't make sense to warn about
something that we don't really control.
How about printing the number of extents only if the allocation fails?
Something like:
if (!sr->sr_extent) {
pr_err("failed to allocate %u sparse read extents\n", count);
return -ENOMEM;
}
Yeah, this also looks good to me.
I will fix it.
Thanks
- Xiubo
Thanks,
Ilya
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