Return-Path: linux-nfs-owner@vger.kernel.org Received: from fieldses.org ([174.143.236.118]:39790 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753244AbaKGVyr (ORCPT ); Fri, 7 Nov 2014 16:54:47 -0500 Date: Fri, 7 Nov 2014 16:54:40 -0500 From: "J. Bruce Fields" To: Jeff Layton Cc: hch@infradead.org, linux-nfs@vger.kernel.org Subject: Re: [PATCH v2] nfsd: convert nfs4_file searches to use RCU Message-ID: <20141107215440.GC5723@fieldses.org> References: <1413541275-3884-1-git-send-email-jlayton@primarydata.com> <1414065662-23341-1-git-send-email-jlayton@primarydata.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1414065662-23341-1-git-send-email-jlayton@primarydata.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Thu, Oct 23, 2014 at 08:01:02AM -0400, Jeff Layton wrote: > The global state_lock protects the file_hashtbl, and that has the > potential to be a scalability bottleneck. > > Address this by making the file_hashtbl use RCU. Add a rcu_head to the > nfs4_file and use that when freeing ones that have been hashed. In order > to conserve space, we union the fi_rcu field with the fi_delegations > list_head which must be clear by the time the last reference to the file > is dropped. > > Convert find_file_locked to use RCU lookup primitives and not to require > that the state_lock be held, and convert find_file to do a lockless > lookup. Convert find_or_add_file to attempt a lockless lookup first, and > then fall back to doing a locked search and insert if that fails to find > anything. > > Also, minimize the number of times we need to calculate the hash value > by passing it in as an argument to the search and insert functions, and > optimize the order of arguments in nfsd4_init_file. OK, looks fine, thanks. Applying for 3.19. In general though I'd like to see more evidence when we're making changes for performance reasons. --b. > > Cc: Christoph Hellwig > Signed-off-by: Jeff Layton > --- > fs/nfsd/nfs4state.c | 51 +++++++++++++++++++++++++++++---------------------- > fs/nfsd/state.h | 5 ++++- > 2 files changed, 33 insertions(+), 23 deletions(-) > > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c > index 1afd7d4420bd..1379d86f7b4f 100644 > --- a/fs/nfsd/nfs4state.c > +++ b/fs/nfsd/nfs4state.c > @@ -275,9 +275,11 @@ opaque_hashval(const void *ptr, int nbytes) > return x; > } > > -static void nfsd4_free_file(struct nfs4_file *f) > +static void nfsd4_free_file_rcu(struct rcu_head *rcu) > { > - kmem_cache_free(file_slab, f); > + struct nfs4_file *fp = container_of(rcu, struct nfs4_file, fi_rcu); > + > + kmem_cache_free(file_slab, fp); > } > > static inline void > @@ -286,9 +288,10 @@ put_nfs4_file(struct nfs4_file *fi) > might_lock(&state_lock); > > if (atomic_dec_and_lock(&fi->fi_ref, &state_lock)) { > - hlist_del(&fi->fi_hash); > + hlist_del_rcu(&fi->fi_hash); > spin_unlock(&state_lock); > - nfsd4_free_file(fi); > + WARN_ON_ONCE(!list_empty(&fi->fi_delegations)); > + call_rcu(&fi->fi_rcu, nfsd4_free_file_rcu); > } > } > > @@ -3057,10 +3060,9 @@ static struct nfs4_file *nfsd4_alloc_file(void) > } > > /* OPEN Share state helper functions */ > -static void nfsd4_init_file(struct nfs4_file *fp, struct knfsd_fh *fh) > +static void nfsd4_init_file(struct knfsd_fh *fh, unsigned int hashval, > + struct nfs4_file *fp) > { > - unsigned int hashval = file_hashval(fh); > - > lockdep_assert_held(&state_lock); > > atomic_set(&fp->fi_ref, 1); > @@ -3073,7 +3075,7 @@ static void nfsd4_init_file(struct nfs4_file *fp, struct knfsd_fh *fh) > fp->fi_share_deny = 0; > memset(fp->fi_fds, 0, sizeof(fp->fi_fds)); > memset(fp->fi_access, 0, sizeof(fp->fi_access)); > - hlist_add_head(&fp->fi_hash, &file_hashtbl[hashval]); > + hlist_add_head_rcu(&fp->fi_hash, &file_hashtbl[hashval]); > } > > void > @@ -3294,17 +3296,14 @@ move_to_close_lru(struct nfs4_ol_stateid *s, struct net *net) > > /* search file_hashtbl[] for file */ > static struct nfs4_file * > -find_file_locked(struct knfsd_fh *fh) > +find_file_locked(struct knfsd_fh *fh, unsigned int hashval) > { > - unsigned int hashval = file_hashval(fh); > struct nfs4_file *fp; > > - lockdep_assert_held(&state_lock); > - > - hlist_for_each_entry(fp, &file_hashtbl[hashval], fi_hash) { > + hlist_for_each_entry_rcu(fp, &file_hashtbl[hashval], fi_hash) { > if (nfsd_fh_match(&fp->fi_fhandle, fh)) { > - get_nfs4_file(fp); > - return fp; > + if (atomic_inc_not_zero(&fp->fi_ref)) > + return fp; > } > } > return NULL; > @@ -3314,10 +3313,11 @@ static struct nfs4_file * > find_file(struct knfsd_fh *fh) > { > struct nfs4_file *fp; > + unsigned int hashval = file_hashval(fh); > > - spin_lock(&state_lock); > - fp = find_file_locked(fh); > - spin_unlock(&state_lock); > + rcu_read_lock(); > + fp = find_file_locked(fh, hashval); > + rcu_read_unlock(); > return fp; > } > > @@ -3325,11 +3325,18 @@ static struct nfs4_file * > find_or_add_file(struct nfs4_file *new, struct knfsd_fh *fh) > { > struct nfs4_file *fp; > + unsigned int hashval = file_hashval(fh); > + > + rcu_read_lock(); > + fp = find_file_locked(fh, hashval); > + rcu_read_unlock(); > + if (fp) > + return fp; > > spin_lock(&state_lock); > - fp = find_file_locked(fh); > - if (fp == NULL) { > - nfsd4_init_file(new, fh); > + fp = find_file_locked(fh, hashval); > + if (likely(fp == NULL)) { > + nfsd4_init_file(fh, hashval, new); > fp = new; > } > spin_unlock(&state_lock); > @@ -4127,7 +4134,7 @@ void nfsd4_cleanup_open_state(struct nfsd4_compound_state *cstate, > nfs4_put_stateowner(so); > } > if (open->op_file) > - nfsd4_free_file(open->op_file); > + kmem_cache_free(file_slab, open->op_file); > if (open->op_stp) > nfs4_put_stid(&open->op_stp->st_stid); > } > diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h > index 8e85e07efce6..9d3be371240a 100644 > --- a/fs/nfsd/state.h > +++ b/fs/nfsd/state.h > @@ -477,7 +477,10 @@ struct nfs4_file { > spinlock_t fi_lock; > struct hlist_node fi_hash; /* hash on fi_fhandle */ > struct list_head fi_stateids; > - struct list_head fi_delegations; > + union { > + struct list_head fi_delegations; > + struct rcu_head fi_rcu; > + }; > /* One each for O_RDONLY, O_WRONLY, O_RDWR: */ > struct file * fi_fds[3]; > /* > -- > 1.9.3 >