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From:   Eric Dumazet <edumazet@google.com>
Date:   Fri, 31 Jul 2020 10:21:08 -0700
Message-ID: <CANn89i+SwhK8XKDqKKvL1svnBWKxv28iKzD2nEf2g0pOO0+0qQ@mail.gmail.com>
Subject: Re: [PATCH net] RDMA/umem: add a schedule point in ib_umem_get()
To:     Jason Gunthorpe <jgg@nvidia.com>
Cc:     Doug Ledford <dledford@redhat.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        linux-rdma <linux-rdma@vger.kernel.org>
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On Fri, Jul 31, 2020 at 10:17 AM Jason Gunthorpe <jgg@nvidia.com> wrote:
>
> On Wed, Jul 29, 2020 at 06:57:55PM -0700, Eric Dumazet wrote:
> > Mapping as little as 64GB can take more than 10 seconds,
> > triggering issues on kernels with CONFIG_PREEMPT_NONE=y.
> >
> > ib_umem_get() already splits the work in 2MB units on x86_64,
> > adding a cond_resched() in the long-lasting loop is enough
> > to solve the issue.
> >
> > Note that sg_alloc_table() can still use more than 100 ms,
> > which is also problematic. This might be addressed later
> > in ib_umem_add_sg_table(), adding new blocks in sgl
> > on demand.
>
> I have seen some patches in progress to do exactly this, the
> motivation is to reduce the memory consumption if a lot of pages are
> combined.

Nice ;)

>
> > Signed-off-by: Eric Dumazet <edumazet@google.com>
> > Cc: Doug Ledford <dledford@redhat.com>
> > Cc: Jason Gunthorpe <jgg@ziepe.ca>
> > Cc: linux-rdma@vger.kernel.org
> > ---
> >  drivers/infiniband/core/umem.c | 1 +
> >  1 file changed, 1 insertion(+)
>
> Why [PATCH net] ?

Sorry, I used a script that I normally use for net submissions, forgot
to remove this tag ;)

>
> Anyhow, applied to rdma for-next

Thanks !

>
> Thanks,
> Jason