netdev - Re: [PATCH RFC 00/30] Overhaul NFSD filecache

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Date:   Thu, 23 Jun 2022 13:27:04 -0700
From:   Frank van der Linden <fvdl@...gle.com>
To:     Chuck Lever <chuck.lever@...cle.com>
Cc:     linux-nfs@...r.kernel.org, netdev@...r.kernel.org,
        david@...morbit.com, tgraf@...g.ch, jlayton@...hat.com
Subject: Re: [PATCH RFC 00/30] Overhaul NFSD filecache

On Wed, Jun 22, 2022 at 7:12 AM Chuck Lever <chuck.lever@...cle.com> wrote:
>
> This series overhauls the NFSD filecache, a cache of server-side
> "struct file" objects recently used by NFS clients. The purposes of
> this overhaul are an immediate improvement in cache scalability in
> the number of open files, and preparation for further improvements.
>
> There are three categories of patches in this series:
>
> 1. Add observability of cache operation so we can see what we're
> doing as changes are made to the code.
>
> 2. Improve the scalability of filecache garbage collection,
> addressing several bugs along the way.
>
> 3. Improve the scalability of the filecache hash table by converting
> it to use rhashtable.
>
> The series as it stands survives typical test workloads. Running
> stress-tests like generic/531 is the next step.
>
> These patches are also available in the linux-nfs-bugzilla-386
> branch of
>
>   https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git
>
> ---
>
> Chuck Lever (30):
>       NFSD: Report filecache LRU size
>       NFSD: Report count of calls to nfsd_file_acquire()
>       NFSD: Report count of freed filecache items
>       NFSD: Report average age of filecache items
>       NFSD: Add nfsd_file_lru_dispose_list() helper
>       NFSD: Refactor nfsd_file_gc()
>       NFSD: Refactor nfsd_file_lru_scan()
>       NFSD: Report the number of items evicted by the LRU walk
>       NFSD: Record number of flush calls
>       NFSD: Report filecache item construction failures
>       NFSD: Zero counters when the filecache is re-initialized
>       NFSD: Hook up the filecache stat file
>       NFSD: WARN when freeing an item still linked via nf_lru
>       NFSD: Trace filecache LRU activity
>       NFSD: Leave open files out of the filecache LRU
>       NFSD: Fix the filecache LRU shrinker
>       NFSD: Never call nfsd_file_gc() in foreground paths
>       NFSD: No longer record nf_hashval in the trace log
>       NFSD: Remove lockdep assertion from unhash_and_release_locked()
>       NFSD: nfsd_file_unhash can compute hashval from nf->nf_inode
>       NFSD: Refactor __nfsd_file_close_inode()
>       NFSD: nfsd_file_hash_remove can compute hashval
>       NFSD: Remove nfsd_file::nf_hashval
>       NFSD: Remove stale comment from nfsd_file_acquire()
>       NFSD: Clean up "open file" case in nfsd_file_acquire()
>       NFSD: Document nfsd_file_cache_purge() API contract
>       NFSD: Replace the "init once" mechanism
>       NFSD: Set up an rhashtable for the filecache
>       NFSD: Convert the filecache to use rhashtable
>       NFSD: Clean up unusued code after rhashtable conversion
>
>
>  fs/nfsd/filecache.c | 677 +++++++++++++++++++++++++++-----------------
>  fs/nfsd/filecache.h |   6 +-
>  fs/nfsd/nfsctl.c    |  10 +
>  fs/nfsd/trace.h     | 117 ++++++--
>  4 files changed, 522 insertions(+), 288 deletions(-)
>
> --
> Chuck Lever
>

Yep, looks good so far, thanks for doing this. Somewhat similar to my (buggy)
attempt at fixing it that I sent at the time (don't put open files on
the LRU, and
use rhashtable), but cleaner and, presumably, less buggy :)

Can't test it right now, but it seems like Wang already confirmed that it works.

- Frank