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From:   Chuck Lever III <chuck.lever@oracle.com>
To:     Mike Javorski <mike.javorski@gmail.com>
CC:     Neil Brown <neilb@suse.de>, Mel Gorman <mgorman@suse.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: NFS server regression in kernel 5.13 (tested w/ 5.13.9)
Thread-Topic: NFS server regression in kernel 5.13 (tested w/ 5.13.9)
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Date:   Fri, 27 Aug 2021 23:49:46 +0000
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> On Aug 27, 2021, at 6:00 PM, Mike Javorski <mike.javorski@gmail.com> wrot=
e:
>=20
> OK, an update. Several hours of spaced out testing sessions and the
> first patch seems to have resolved the issue. There may be a very tiny
> bit of lag that still occurs when opening/processing new files, but so
> far on this kernel I have not had any multi-second freezes. I am still
> waiting on the kernel with Neil's patch to compile (compiling on this
> underpowered server so it's taking several hours), but I think the
> testing there will just be to see if I can show it works still, and
> then to try and test in a memory constrained VM. To see if I can
> recreate Neil's experiment. Likely will have to do this over the
> weekend given the kernel compile delay + fiddling with a VM.

Thanks for your testing!


> Chuck: I don't mean to overstep bounds, but is it possible to get that
> patch pulled into 5.13 stable? That may help things for several people
> while 5.14 goes through it's shakedown in archlinux prior to release.

The patch had a Fixes: tag, so it should get automatically backported
to every kernel that has the broken commit. If you don't see it in
a subsequent 5.13 stable kernel, you are free to ask the stable
maintainers to consider it.


> - mike
>=20
> On Fri, Aug 27, 2021 at 10:07 AM Mike Javorski <mike.javorski@gmail.com> =
wrote:
>>=20
>> Chuck:
>> I just booted a 5.13.13 kernel with your suggested patch. No freezes
>> on the first test, but that sometimes happens so I will let the server
>> settle some and try it again later in the day (which also would align
>> with Neil's comment on memory fragmentation being a contributor).
>>=20
>> Neil:
>> I have started a compile with the above kernel + your patch to test
>> next unless you or Chuck determine that it isn't needed, or that I
>> should test both patches discreetly. As the above is already merged to
>> 5.14 it seemed logical to just add your patch on top.
>>=20
>> I will also try to set up a vm to test your md5sum scenario with the
>> various kernels since it's a much faster thing to test.
>>=20
>> - mike
>>=20
>> On Fri, Aug 27, 2021 at 7:13 AM Chuck Lever III <chuck.lever@oracle.com>=
 wrote:
>>>=20
>>>=20
>>>> On Aug 27, 2021, at 3:14 AM, NeilBrown <neilb@suse.de> wrote:
>>>>=20
>>>> Subject: [PATCH] SUNRPC: don't pause on incomplete allocation
>>>>=20
>>>> alloc_pages_bulk_array() attempts to allocate at least one page based =
on
>>>> the provided pages, and then opportunistically allocates more if that
>>>> can be done without dropping the spinlock.
>>>>=20
>>>> So if it returns fewer than requested, that could just mean that it
>>>> needed to drop the lock.  In that case, try again immediately.
>>>>=20
>>>> Only pause for a time if no progress could be made.
>>>=20
>>> The case I was worried about was "no pages available on the
>>> pcplist", in which case, alloc_pages_bulk_array() resorts
>>> to calling __alloc_pages() and returns only one new page.
>>>=20
>>> "No progess" would mean even __alloc_pages() failed.
>>>=20
>>> So this patch would behave essentially like the
>>> pre-alloc_pages_bulk_array() code: call alloc_page() for
>>> each empty struct_page in the array without pausing. That
>>> seems correct to me.
>>>=20
>>>=20
>>> I would add
>>>=20
>>> Fixes: f6e70aab9dfe ("SUNRPC: refresh rq_pages using a bulk page alloca=
tor")
>>>=20
>>>=20
>>>> Signed-off-by: NeilBrown <neilb@suse.de>
>>>> ---
>>>> net/sunrpc/svc_xprt.c | 7 +++++--
>>>> 1 file changed, 5 insertions(+), 2 deletions(-)
>>>>=20
>>>> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
>>>> index d66a8e44a1ae..99268dd95519 100644
>>>> --- a/net/sunrpc/svc_xprt.c
>>>> +++ b/net/sunrpc/svc_xprt.c
>>>> @@ -662,7 +662,7 @@ static int svc_alloc_arg(struct svc_rqst *rqstp)
>>>> {
>>>>      struct svc_serv *serv =3D rqstp->rq_server;
>>>>      struct xdr_buf *arg =3D &rqstp->rq_arg;
>>>> -     unsigned long pages, filled;
>>>> +     unsigned long pages, filled, prev;
>>>>=20
>>>>      pages =3D (serv->sv_max_mesg + 2 * PAGE_SIZE) >> PAGE_SHIFT;
>>>>      if (pages > RPCSVC_MAXPAGES) {
>>>> @@ -672,11 +672,14 @@ static int svc_alloc_arg(struct svc_rqst *rqstp)
>>>>              pages =3D RPCSVC_MAXPAGES;
>>>>      }
>>>>=20
>>>> -     for (;;) {
>>>> +     for (prev =3D 0;; prev =3D filled) {
>>>>              filled =3D alloc_pages_bulk_array(GFP_KERNEL, pages,
>>>>                                              rqstp->rq_pages);
>>>>              if (filled =3D=3D pages)
>>>>                      break;
>>>> +             if (filled > prev)
>>>> +                     /* Made progress, don't sleep yet */
>>>> +                     continue;
>>>>=20
>>>>              set_current_state(TASK_INTERRUPTIBLE);
>>>>              if (signalled() || kthread_should_stop()) {
>>>=20
>>> --
>>> Chuck Lever
>>>=20
>>>=20
>>>=20

--
Chuck Lever