Re: [PATCH] netfs: Add retry stat counters

David Howells
2025-02-10T23:19:10Z

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

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.

Thanks,
David