Re: Possible bug report: kernel 6.5.0/6.5.1 high load when CIFS share is mounted (cifsd-cfid-laundromat in"D" state)

matoro
2023-10-13T23:20:43Z

On 2023-10-05 05:55, Dr. Bernd Feige wrote:
> Am Dienstag, dem 26.09.2023 um 17:54 -0700 schrieb Paul Aurich:
>> Perhaps the laundromat thread should be using msleep_interruptible()?
>>
>> Using an interruptible sleep appears to prevent the thread from
>> contributing
>> to the load average, and has the happy side-effect of removing the
>> up-to-1s delay
>> when tearing down the tcon (since a7c01fa93ae, kthread_stop() will
>> return
>> early triggered by kthread_stop).
>
> Sorry for chiming in so late - I'm also on gentoo (kernel 6.5.5-
> gentoo), but as a client of Windows AD.
>
> Just want to emphasize that using uninterruptible sleep has not just
> unhappy but devastating side-effects.
>
> I have 8 processors and 16 cifsd-cfid-laundromat processes, so
> /proc/loadavg reports a load average of 16 on a totally idle system.
>
> This means that load-balancing software will never start additional
> tasks on this system - "make -l" but also any other load-dependent
> system. Just reducing the number of cifsd-cfid-laundromat processes
> does not fix this - even a single one makes loadavg report a wrong
> result for load balancing.
>
> So, if cifsd-cfid-laundromat must really be uninterruptible, the only
> solution would be to change the way loadavg is computed by the kernel
> to exclude uninterruptible but sleeping processes. But must it be
> uninterruptible?
>
> Thanks and best regards,
> Bernd

This is a huge problem here as well, as a client to Samba using SMB1
(for Unix extensions).

For others encountering this problem, I was able to work around it with
the following snippet:

diff --git a/fs/smb/client/cached_dir.c b/fs/smb/client/cached_dir.c
index 2d5e9a9d5b8b..fc2caccb597a 100644
--- a/fs/smb/client/cached_dir.c
+++ b/fs/smb/client/cached_dir.c
@@ -576,7 +576,7 @@ cifs_cfids_laundromat_thread(void *p)
struct list_head entry;

while (!kthread_should_stop()) {
- ssleep(1);
+ msleep_interruptible(1000);
INIT_LIST_HEAD(&entry);
if (kthread_should_stop())
return 0;