Re: NFS server regression in kernel 5.13 (tested w/ 5.13.9)

[Mike Javorski <mike.javorski@gmail.com>]

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).

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.

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.

- mike

On Fri, Aug 27, 2021 at 7:13 AM Chuck Lever III <chuck.lever@oracle.com> wrote:
>
>
> > On Aug 27, 2021, at 3:14 AM, NeilBrown <neilb@suse.de> wrote:
> >
> > Subject: [PATCH] SUNRPC: don't pause on incomplete allocation
> >
> > 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.
> >
> > So if it returns fewer than requested, that could just mean that it
> > needed to drop the lock.  In that case, try again immediately.
> >
> > Only pause for a time if no progress could be made.
>
> 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.
>
> "No progess" would mean even __alloc_pages() failed.
>
> 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.
>
>
> I would add
>
> Fixes: f6e70aab9dfe ("SUNRPC: refresh rq_pages using a bulk page allocator")
>
>
> > Signed-off-by: NeilBrown <neilb@suse.de>
> > ---
> > net/sunrpc/svc_xprt.c | 7 +++++--
> > 1 file changed, 5 insertions(+), 2 deletions(-)
> >
> > 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 = rqstp->rq_server;
> >       struct xdr_buf *arg = &rqstp->rq_arg;
> > -     unsigned long pages, filled;
> > +     unsigned long pages, filled, prev;
> >
> >       pages = (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 = RPCSVC_MAXPAGES;
> >       }
> >
> > -     for (;;) {
> > +     for (prev = 0;; prev = filled) {
> >               filled = alloc_pages_bulk_array(GFP_KERNEL, pages,
> >                                               rqstp->rq_pages);
> >               if (filled == pages)
> >                       break;
> > +             if (filled > prev)
> > +                     /* Made progress, don't sleep yet */
> > +                     continue;
> >
> >               set_current_state(TASK_INTERRUPTIBLE);
> >               if (signalled() || kthread_should_stop()) {
>
> --
> Chuck Lever
>
>
>