Re: [PATCH] netfs: Add retry stat counters

Ihor Solodrai
2025-02-11T00:54:47Z

On 2/10/25 3:18 PM, David Howells wrote:
> Ihor Solodrai <ihor.solodrai@linux.dev> wrote:
>
>> Done. I pushed the logs to the previously mentioned github branch:
>> https://github.com/kernel-patches/bpf/commit/699a3bb95e2291d877737438fb641628702fd18f
>
> Perfect, thanks.
>
> Looking at the last record of /proc/fs/netfs/requests, I see:
>
> REQUEST OR REF FL ERR OPS COVERAGE
> ======== == === == ==== === =========
> 00000a98 RA 1 2001 0 0 @0000 2000/2000
>
> So the request of interest is R=00000a98 in the trace. Grepping for that, I
> see (with a few columns cut out):
>
> test_progs-no_a-97: netfs_rreq_ref: R=00000a98 NEW r=1
> test_progs-no_a-97: netfs_read: R=00000a98 READAHEAD c=00000000 ni=2ec02f16 s=0 l=2000 sz=17a8
> test_progs-no_a-97: netfs_rreq_ref: R=00000a98 GET SUBREQ r=2
> test_progs-no_a-97: netfs_sreq: R=00000a98[1] DOWN TERM f=192 s=0 17a8/17a8 s=1 e=0
> test_progs-no_a-97: netfs_rreq_ref: R=00000a98 GET WORK r=3
> test_progs-no_a-97: netfs_sreq_ref: R=00000a98[1] PUT TERM r=1
> test_progs-no_a-97: netfs_rreq_ref: R=00000a98 GET SUBREQ r=4
> test_progs-no_a-97: netfs_sreq: R=00000a98[2] ZERO SUBMT f=00 s=17a8 0/858 s=0 e=0
> kworker/u8:2-36: netfs_rreq_ref: R=00000a98 SEE WORK r=4
> kworker/u8:2-36: netfs_rreq: R=00000a98 RA COLLECT f=2021
> kworker/u8:2-36: netfs_sreq: R=00000a98[1] DOWN DSCRD f=92 s=0 17a8/17a8 s=1 e=0
> kworker/u8:2-36: netfs_sreq_ref: R=00000a98[1] PUT DONE r=0
> kworker/u8:2-36: netfs_sreq: R=00000a98[1] DOWN FREE f=92 s=0 17a8/17a8 s=1 e=0
> kworker/u8:2-36: netfs_rreq_ref: R=00000a98 PUT SUBREQ r=3
> kworker/u8:2-36: netfs_rreq: R=00000a98 RA COMPLET f=2021
> kworker/u8:2-36: netfs_rreq: R=00000a98 RA WAKE-IP f=2021
> kworker/u8:2-36: netfs_rreq: R=00000a98 RA DONE f=2001
> kworker/u8:2-36: netfs_rreq_ref: R=00000a98 PUT WORK r=2
> test_progs-no_a-97: netfs_sreq: R=00000a98[2] ZERO TERM f=102 s=17a8 858/858 s=1 e=0
> test_progs-no_a-97: netfs_rreq_ref: R=00000a98 GET WORK r=3
> test_progs-no_a-97: netfs_sreq_ref: R=00000a98[2] PUT TERM r=1
> test_progs-no_a-97: netfs_rreq_ref: R=00000a98 PUT RETURN r=2
> kworker/u8:2-36: netfs_rreq_ref: R=00000a98 SEE WORK r=2
> kworker/u8:2-36: netfs_rreq_ref: R=00000a98 PUT WORK r=1
>
> You can see subrequest 1 completes fine, the subrequest is freed and the ref
> it had on the request is put:
>
> netfs_sreq: R=00000a98[1] DOWN FREE f=92 s=0 17a8/17a8 s=1 e=0
> netfs_rreq_ref: R=00000a98 PUT SUBREQ r=3
>
> Subrequest 2, however isn't collected:
>
> netfs_sreq: R=00000a98[2] ZERO SUBMT f=00 s=17a8 0/858 s=0 e=0
> netfs_sreq: R=00000a98[2] ZERO TERM f=102 s=17a8 858/858 s=1 e=0
> netfs_sreq_ref: R=00000a98[2] PUT TERM r=1
>
> and the work happens again in kworker/u8:2-36 right at the end:
>
> netfs_rreq_ref: R=00000a98 SEE WORK r=2
> netfs_rreq_ref: R=00000a98 PUT WORK r=1
>
> but this doesn't do anything.
>
> The excess buffer clearance happened in the app thread (test_progs-no_a-97):
>
> netfs_sreq: R=00000a98[2] ZERO TERM f=102 s=17a8 858/858 s=1 e=0
>
>> Let me know if I can help with anything else.
>
> Can you add some more tracepoints?
>
> echo 1 >/sys/kernel/debug/tracing/events/netfs/netfs_collect/enable
> echo 1 >/sys/kernel/debug/tracing/events/netfs/netfs_collect_sreq/enable
> echo 1 >/sys/kernel/debug/tracing/events/netfs/netfs_collect_state/enable

See here: https://github.com/kernel-patches/bpf/commit/517f51d1f6c09ebab9df3e3d17bb669601ab14ef

Beware, uncompressed trace-cmd.log is 37Mb

>
> However, I think I may have spotted the issue: I'm mixing
> clear_and_wake_up_bit() for NETFS_RREQ_IN_PROGRESS (which will use a common
> system waitqueue) with waiting on an rreq-specific waitqueue in such as
> netfs_wait_for_read().
>
> I'll work up a fix patch for that tomorrow.

Great! Thank you.

>
> Thanks,
> David
>