Re: nfsd: unable to allocate nfsd_file_hashtbl

[Jeff Layton <jlayton@kernel.org>]

On Thu, 2022-02-24 at 12:13 +0200, Amir Goldstein wrote:
> Hi Jeff,
> 
> I got some reports from customers about failure to allocate the
> nfsd_file_hashtbl on nfs server restart on a long running system,
> probably due to memory fragmentation.
> 
> A search in Google for this error message yields several results of
> similar reports [1][2].
> 
> My question is, does nfsd_file_cache_init() have to be done on server
> startup?
> 
> Doesn't it make more sense to allocate all the memory pools and
> hash table on init_nfsd()?
> 
> Thanks,
> Amir.
> 
> [1] https://unix.stackexchange.com/questions/640534/nfs-cannot-allocate-memory
> [2] https://askubuntu.com/questions/1365821/nfs-crashing-on-ubuntu-server-20-04

That is a big allocation. On my box, nfsd_fcache_bucket is 80 bytes, so
we end up needing 80 contiguous pages to allocate the whole table. It
doesn't surprise me that it fails sometimes.

We could just allocate it on init_nfsd, but that happens when the module
is plugged in and we'll lose 80 pages when people plug it in (or build
it in) and don't actually use nfsd.

The other option might be to just use kvcalloc? It's not a frequent
allocation, so I don't think performance would be an issue. We had
similar reports several years ago with nfsd_reply_cache_init, and using
kvzalloc ended up taking care of it.

-- 
Jeff Layton <jlayton@kernel.org>