On Sat, 2022-07-09 at 20:45 +0000, Chuck Lever III wrote: > > > On Jul 8, 2022, at 3:29 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote: > > > > 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. > > My measurements indicate that 2->1 is the common case, so checking > that this is /not/ a 2->1 transition doesn't confer much if any > benefit. > > Under load, I don't see any contention on the LRU locks, which is > where I'd expect to see a problem if this design were not efficient. > > Fair enough. I guess the idea is to throw it onto the LRU and the scanner will just (eventually) take it off again without reaping it. You can add my Reviewed-by: to this one as well. > > > 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> > > -- > Chuck Lever > > > -- Jeff Layton <jlayton@xxxxxxxxxx>
