On Fri, 2022-07-08 at 14:25 -0400, Chuck Lever wrote: > There have been reports of problems when running fstests generic/531 > against Linux NFS servers with NFSv4. The NFS server that hosts the > test's SCRATCH_DEV suffers from CPU soft lock-ups during the test. > Analysis shows that: > > fs/nfsd/filecache.c > 482 ret = list_lru_walk(&nfsd_file_lru, > 483 nfsd_file_lru_cb, > 484 &head, LONG_MAX); > > causes nfsd_file_gc() to walk the entire length of the filecache LRU > list every time it is called (which is quite frequently). The walk > holds a spinlock the entire time that prevents other nfsd threads > from accessing the filecache. > > What's more, for NFSv4 workloads, none of the items that are visited > during this walk may be evicted, since they are all files that are > held OPEN by NFS clients. > > Address this by ensuring that open files are not kept on the LRU > list. > > Reported-by: Frank van der Linden <fllinden@xxxxxxxxxx> > Reported-by: Wang Yugui <wangyugui@xxxxxxxxxxxx> > Link: https://bugzilla.linux-nfs.org/show_bug.cgi?id=386 > Suggested-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> > Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx> > --- > fs/nfsd/filecache.c | 24 +++++++++++++++++++----- > fs/nfsd/trace.h | 2 ++ > 2 files changed, 21 insertions(+), 5 deletions(-) > > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c > index 37373b012276..6e9e186334ab 100644 > --- a/fs/nfsd/filecache.c > +++ b/fs/nfsd/filecache.c > @@ -269,6 +269,7 @@ nfsd_file_flush(struct nfsd_file *nf) > > static void nfsd_file_lru_add(struct nfsd_file *nf) > { > + set_bit(NFSD_FILE_REFERENCED, &nf->nf_flags); > if (list_lru_add(&nfsd_file_lru, &nf->nf_lru)) > trace_nfsd_file_lru_add(nf); > } > @@ -298,7 +299,6 @@ nfsd_file_unhash(struct nfsd_file *nf) > { > if (test_and_clear_bit(NFSD_FILE_HASHED, &nf->nf_flags)) { > nfsd_file_do_unhash(nf); > - nfsd_file_lru_remove(nf); > return true; > } > return false; > @@ -319,6 +319,7 @@ nfsd_file_unhash_and_release_locked(struct nfsd_file *nf, struct list_head *disp > if (refcount_dec_not_one(&nf->nf_ref)) > return true; > > + nfsd_file_lru_remove(nf); > list_add(&nf->nf_lru, dispose); > return true; > } > @@ -330,6 +331,7 @@ nfsd_file_put_noref(struct nfsd_file *nf) > > if (refcount_dec_and_test(&nf->nf_ref)) { > WARN_ON(test_bit(NFSD_FILE_HASHED, &nf->nf_flags)); > + nfsd_file_lru_remove(nf); > nfsd_file_free(nf); > } > } > @@ -339,7 +341,7 @@ nfsd_file_put(struct nfsd_file *nf) > { > might_sleep(); > > - set_bit(NFSD_FILE_REFERENCED, &nf->nf_flags); > + nfsd_file_lru_add(nf); Do you really want to add this on every put? I would have thought you'd only want to do this on a 2->1 nf_ref transition. > if (test_bit(NFSD_FILE_HASHED, &nf->nf_flags) == 0) { > nfsd_file_flush(nf); > nfsd_file_put_noref(nf); > @@ -439,8 +441,18 @@ nfsd_file_dispose_list_delayed(struct list_head *dispose) > } > } > > -/* > +/** > + * nfsd_file_lru_cb - Examine an entry on the LRU list > + * @item: LRU entry to examine > + * @lru: controlling LRU > + * @lock: LRU list lock (unused) > + * @arg: dispose list > + * > * Note this can deadlock with nfsd_file_cache_purge. > + * > + * Return values: > + * %LRU_REMOVED: @item was removed from the LRU > + * %LRU_SKIP: @item cannot be evicted > */ > static enum lru_status > nfsd_file_lru_cb(struct list_head *item, struct list_lru_one *lru, > @@ -462,8 +474,9 @@ nfsd_file_lru_cb(struct list_head *item, struct list_lru_one *lru, > * That order is deliberate to ensure that we can do this locklessly. > */ > if (refcount_read(&nf->nf_ref) > 1) { > + list_lru_isolate(lru, &nf->nf_lru); > trace_nfsd_file_gc_in_use(nf); > - return LRU_SKIP; > + return LRU_REMOVED; Interesting. So you wait until the LRU scanner runs to remove these entries? I expected to see you do this in nfsd_file_get, but this does seem likely to be more efficient. > } > > /* > @@ -1020,6 +1033,7 @@ nfsd_do_file_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp, > goto retry; > } > > + nfsd_file_lru_remove(nf); > this_cpu_inc(nfsd_file_cache_hits); > > if (!(may_flags & NFSD_MAY_NOT_BREAK_LEASE)) { > @@ -1055,7 +1069,6 @@ nfsd_do_file_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp, > refcount_inc(&nf->nf_ref); > __set_bit(NFSD_FILE_HASHED, &nf->nf_flags); > __set_bit(NFSD_FILE_PENDING, &nf->nf_flags); > - nfsd_file_lru_add(nf); > hlist_add_head_rcu(&nf->nf_node, &nfsd_file_hashtbl[hashval].nfb_head); > ++nfsd_file_hashtbl[hashval].nfb_count; > nfsd_file_hashtbl[hashval].nfb_maxcount = max(nfsd_file_hashtbl[hashval].nfb_maxcount, > @@ -1080,6 +1093,7 @@ nfsd_do_file_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp, > */ > if (status != nfs_ok || inode->i_nlink == 0) { > bool do_free; > + nfsd_file_lru_remove(nf); > spin_lock(&nfsd_file_hashtbl[hashval].nfb_lock); > do_free = nfsd_file_unhash(nf); > spin_unlock(&nfsd_file_hashtbl[hashval].nfb_lock); > diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h > index 1cc1133371eb..54082b868b72 100644 > --- a/fs/nfsd/trace.h > +++ b/fs/nfsd/trace.h > @@ -929,7 +929,9 @@ DEFINE_EVENT(nfsd_file_gc_class, name, \ > TP_ARGS(nf)) > > DEFINE_NFSD_FILE_GC_EVENT(nfsd_file_lru_add); > +DEFINE_NFSD_FILE_GC_EVENT(nfsd_file_lru_add_disposed); > DEFINE_NFSD_FILE_GC_EVENT(nfsd_file_lru_del); > +DEFINE_NFSD_FILE_GC_EVENT(nfsd_file_lru_del_disposed); > DEFINE_NFSD_FILE_GC_EVENT(nfsd_file_gc_in_use); > DEFINE_NFSD_FILE_GC_EVENT(nfsd_file_gc_writeback); > DEFINE_NFSD_FILE_GC_EVENT(nfsd_file_gc_referenced); > > -- Jeff Layton <jlayton@xxxxxxxxxx>
