On Fri, 2022-07-08 at 14:25 -0400, Chuck Lever wrote:
> The checks in nfsd_file_acquire() and nfsd_file_put() that directly
> invoke filecache garbage collection are intended to keep cache
> occupancy between a low- and high-watermark. The reason to limit the
> capacity of the filecache is to keep filecache lookups reasonably
> fast.
>
> However, invoking garbage collection at those points has some
> undesirable negative impacts. Files that are held open by NFSv4
> clients often push the occupancy of the filecache over these
> watermarks. At that point:
>
> - Every call to nfsd_file_acquire() and nfsd_file_put() results in
> an LRU walk. This has the same effect on lookup latency as long
> chains in the hash table.
> - Garbage collection will then run on every nfsd thread, causing a
> lot of unnecessary lock contention.
> - Limiting cache capacity pushes out files used only by NFSv3
> clients, which are the type of files the filecache is supposed to
> help.
>
> To address those negative impacts, remove the direct calls to the
> garbage collector. Subsequent patches will address maintaining
> lookup efficiency as cache capacity increases.
>
> Suggested-by: Wang Yugui <wangyugui@xxxxxxxxxxxx>
> Suggested-by: Dave Chinner <david@xxxxxxxxxxxxx>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> ---
> fs/nfsd/filecache.c | 10 +---------
> 1 file changed, 1 insertion(+), 9 deletions(-)
>
> diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
> index bd6ba63f69ae..faa8588663d6 100644
> --- a/fs/nfsd/filecache.c
> +++ b/fs/nfsd/filecache.c
> @@ -29,8 +29,6 @@
> #define NFSD_LAUNDRETTE_DELAY (2 * HZ)
>
> #define NFSD_FILE_SHUTDOWN (1)
> -#define NFSD_FILE_LRU_THRESHOLD (4096UL)
> -#define NFSD_FILE_LRU_LIMIT (NFSD_FILE_LRU_THRESHOLD << 2)
>
> /* We only care about NFSD_MAY_READ/WRITE for this cache */
> #define NFSD_FILE_MAY_MASK (NFSD_MAY_READ|NFSD_MAY_WRITE)
> @@ -66,8 +64,6 @@ static struct fsnotify_group *nfsd_file_fsnotify_group;
> static atomic_long_t nfsd_filecache_count;
> static struct delayed_work nfsd_filecache_laundrette;
>
> -static void nfsd_file_gc(void);
> -
> static void
> nfsd_file_schedule_laundrette(void)
> {
> @@ -350,9 +346,6 @@ nfsd_file_put(struct nfsd_file *nf)
> nfsd_file_schedule_laundrette();
> } else
> nfsd_file_put_noref(nf);
> -
> - if (atomic_long_read(&nfsd_filecache_count) >= NFSD_FILE_LRU_LIMIT)
> - nfsd_file_gc();
This may be addressed in later patches, but instead of just removing
these, would it be better to instead call
nfsd_file_schedule_laundrette() ?
> }
>
> struct nfsd_file *
> @@ -1075,8 +1068,7 @@ nfsd_do_file_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
> nfsd_file_hashtbl[hashval].nfb_maxcount = max(nfsd_file_hashtbl[hashval].nfb_maxcount,
> nfsd_file_hashtbl[hashval].nfb_count);
> spin_unlock(&nfsd_file_hashtbl[hashval].nfb_lock);
> - if (atomic_long_inc_return(&nfsd_filecache_count) >= NFSD_FILE_LRU_THRESHOLD)
> - nfsd_file_gc();
> + atomic_long_inc(&nfsd_filecache_count);
>
> nf->nf_mark = nfsd_file_mark_find_or_create(nf);
> if (nf->nf_mark) {
>
>
--
Jeff Layton <jlayton@xxxxxxxxxx>
