Re: [External] : nfsd: memory leak when client does many file operations

[Benjamin Coddington]

On 25 Mar 2024, at 16:11, Chuck Lever III wrote:

>> On Mar 25, 2024, at 3:55 PM, Jan Schunk <scpcom@xxxxxx> wrote:
>>
>> The VM is now running 20 hours with 512MB RAM, no desktop, without the "noatime" mount option and without the "async" export option.
>>
>> Currently there is no issue, but the memory usage is still contantly growing. It may just take longer before something happens.
>>
>> top - 00:49:49 up 3 min,  1 user,  load average: 0,21, 0,19, 0,09
>> Tasks: 111 total,   1 running, 110 sleeping,   0 stopped,   0 zombie
>> %CPU(s):  0,2 us,  0,3 sy,  0,0 ni, 99,5 id,  0,0 wa,  0,0 hi,  0,0 si,  0,0 st
>> MiB Spch:    467,0 total,    302,3 free,     89,3 used,     88,1 buff/cache
>> MiB Swap:    975,0 total,    975,0 free,      0,0 used.    377,7 avail Spch
>>
>> top - 15:05:39 up 14:19,  1 user,  load average: 1,87, 1,72, 1,65
>> Tasks: 104 total,   1 running, 103 sleeping,   0 stopped,   0 zombie
>> %CPU(s):  0,2 us,  4,9 sy,  0,0 ni, 53,3 id, 39,0 wa,  0,0 hi,  2,6 si,  0,0 st
>> MiB Spch:    467,0 total,     21,2 free,    147,1 used,    310,9 buff/cache
>> MiB Swap:    975,0 total,    952,9 free,     22,1 used.    319,9 avail Spch
>>
>> top - 20:48:16 up 20:01,  1 user,  load average: 5,02, 2,72, 2,08
>> Tasks: 104 total,   5 running,  99 sleeping,   0 stopped,   0 zombie
>> %CPU(s):  0,2 us, 46,4 sy,  0,0 ni, 11,9 id,  2,3 wa,  0,0 hi, 39,2 si,  0,0 st
>> MiB Spch:    467,0 total,     16,9 free,    190,8 used,    271,6 buff/cache
>> MiB Swap:    975,0 total,    952,9 free,     22,1 used.    276,2 avail Spch
>
> I don't see anything in your original memory dump that
> might account for this. But I'm at a loss because I'm
> a kernel developer, not a support guy -- I don't have
> any tools or expertise that can troubleshoot a system
> without rebuilding a kernel with instrumentation. My
> first instinct is to tell you to bisect between v6.3
> and v6.4, or at least enable kmemleak, but I'm guessing
> you don't build your own kernels.
>
> My only recourse at this point would be to try to
> reproduce it myself, but unfortunately I've just
> upgraded my whole lab to Fedora 39, and there's a grub
> bug that prevents booting any custom-built kernel
> on my hardware.
>
> So I'm stuck until I can nail that down. Anyone else
> care to help out?

Sure - I can throw some stuff..

Can we dig into which memory slabs might be growing?  Something like:

watch -d "cat /proc/slabinfo | grep nfsd"

.. for a bit might show what is growing.

Then use a systemtap script like the one below to trace the allocations - use:

stap -v --all-modules kmem_alloc.stp <slab_name>

Ben


8<---------------------------- save as kmem_alloc.stp ----------------------------

# This script displays the number of given slab allocations and the backtraces leading up to it.

global slab = @1
global stats, stacks
probe kernel.function("kmem_cache_alloc") {
        if (kernel_string($s->name) == slab) {
                stats[execname()] <<< 1
                stacks[execname(),kernel_string($s->name),backtrace()] <<< 1
        }
}
# Exit after 10 seconds
# probe timer.ms(10000) { exit () }
probe end {
        printf("Number of %s slab allocations by process\n", slab)
        foreach ([exec] in stats) {
                printf("%s:\t%d\n",exec,@count(stats[exec]))
        }
        printf("\nBacktrace of processes when allocating\n")
        foreach ([proc,cache,bt] in stacks) {
                printf("Exec: %s Name: %s  Count: %d\n",proc,cache,@count(stacks[proc,cache,bt]))
                print_stack(bt)
                printf("\n-------------------------------------------------------\n\n")
        }
}