Bug#898137: nfsd: increase DRC cache limit
Control: tags -1 + pending
Hi Sergio,
On Mon, May 07, 2018 at 09:40:08PM +0200, Sergio Gelato wrote:
> Source: linux
> Version: 4.9.88-1
> Severity: wishlist
> Tags: patch
>
> I've run into this capacity limitation in stretch, which is addressed
> upstream in Linux 4.15 by the following commit:
>
> commit 44d8660d3bb0a1c8363ebcb906af2343ea8e15f6
> Author: J. Bruce Fields <bfields@redhat.com>
> Date: Tue Sep 19 20:51:31 2017 -0400
>
> nfsd: increase DRC cache limit
>
> which trivially applies to Linux 4.9 (I haven't checked 3.16) and provides
> significant relief in my use case. It would save me (and perhaps others)
> work if this change could be included in Debian's 4.9 kernel packages;
> otherwise I'll have to keep maintaining my own fork. (4.15 has other
> issues so I don't want to use it in production yet.)
>
> For the benefit of others who may be running into the same problem, here
> is a more detailed description.
>
> Symptom: an NFS server accepts only a limited number of concurrent v4.1+
> mounts. Once that limit is reached, new clients get NFS4ERR_DELAY (10008)
> replies to CREATE_SESSION. (This can be seen in the server's dmesg after
> rpcdebug -m nfsd -s proc.) Increasing the number of nfsd threads has no
> impact on the number of mounts allowed. A server with 512MB of RAM
> only accepts 7 or 8 concurrent NFSv4.1+ mounts. From the perspective of
> an affected client, mount.nfs appears to hang (triggering a kernel backtrace
> after 120 seconds); in reality, though, it just keeps reissuing CREATE_SESSION
> calls until one of them succeeds.
>
> Pre-v4.1 clients are unaffected by this since sessions are new to NFS v4.1.
>
> The proposed patch just increases the limit by an order of magnitude, at
> the cost of using more kernel memory. As noted in comments in the source
> code, it would be nice to make this tuneable by the server administrator.
Alright, I have added 44d8660d3bb0a1c8363ebcb906af2343ea8e15f6 in the
stretch branch, so it will be included in the next point release
update for src:linux packages.
Regards,
Salvatore
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