From 210ad6aedb332e73167ece5af9bd47f0da8c2aca Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Mon, 8 Jun 2009 15:22:25 -0400 Subject: ext4: avoid unnecessary spinlock in critical POSIX ACL path If a filesystem supports POSIX ACL's, the VFS layer expects the filesystem to do POSIX ACL checks on any files not owned by the caller, and it does this for every single pathname component that it looks up. That obviously can be pretty expensive if the filesystem isn't careful about it, especially with locking. That's doubly sad, since the common case tends to be that there are no ACL's associated with the files in question. ext4 already caches the ACL data so that it doesn't have to look it up over and over again, but it does so by taking the inode->i_lock spinlock on every lookup. Which is a noticeable overhead even if it's a private lock, especially on CPU's where the serialization is expensive (eg Intel Netburst aka 'P4'). For the special case of not actually having any ACL's, all that locking is unnecessary. Even if somebody else were to be changing the ACL's on another CPU, we simply don't care - if we've seen a NULL ACL, we might as well use it. So just load the ACL speculatively without any locking, and if it was NULL, just use it. If it's non-NULL (either because we had a cached entry, or because the cache hasn't been filled in at all), it means that we'll need to get the lock and re-load it properly. (This commit was ported from a patch originally authored by Linus for ext3.) Signed-off-by: "Theodore Ts'o" Signed-off-by: Al Viro --- fs/ext4/acl.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) (limited to 'fs/ext4/acl.c') diff --git a/fs/ext4/acl.c b/fs/ext4/acl.c index 647e0d65a284..605aeed96d68 100644 --- a/fs/ext4/acl.c +++ b/fs/ext4/acl.c @@ -129,12 +129,15 @@ fail: static inline struct posix_acl * ext4_iget_acl(struct inode *inode, struct posix_acl **i_acl) { - struct posix_acl *acl = EXT4_ACL_NOT_CACHED; + struct posix_acl *acl = ACCESS_ONCE(*i_acl); - spin_lock(&inode->i_lock); - if (*i_acl != EXT4_ACL_NOT_CACHED) - acl = posix_acl_dup(*i_acl); - spin_unlock(&inode->i_lock); + if (acl) { + spin_lock(&inode->i_lock); + acl = *i_acl; + if (acl != EXT4_ACL_NOT_CACHED) + acl = posix_acl_dup(acl); + spin_unlock(&inode->i_lock); + } return acl; } -- cgit v1.2.3 From d4bfe2f76d785cc77611a4bda8cedaff358d8c7d Mon Sep 17 00:00:00 2001 From: Al Viro Date: Mon, 8 Jun 2009 19:54:26 -0400 Subject: switch ext4 to inode->i_acl Signed-off-by: Al Viro --- fs/ext4/acl.c | 22 ++++++++++------------ 1 file changed, 10 insertions(+), 12 deletions(-) (limited to 'fs/ext4/acl.c') diff --git a/fs/ext4/acl.c b/fs/ext4/acl.c index 605aeed96d68..0084e3a19d86 100644 --- a/fs/ext4/acl.c +++ b/fs/ext4/acl.c @@ -134,7 +134,7 @@ ext4_iget_acl(struct inode *inode, struct posix_acl **i_acl) if (acl) { spin_lock(&inode->i_lock); acl = *i_acl; - if (acl != EXT4_ACL_NOT_CACHED) + if (acl != ACL_NOT_CACHED) acl = posix_acl_dup(acl); spin_unlock(&inode->i_lock); } @@ -147,7 +147,7 @@ ext4_iset_acl(struct inode *inode, struct posix_acl **i_acl, struct posix_acl *acl) { spin_lock(&inode->i_lock); - if (*i_acl != EXT4_ACL_NOT_CACHED) + if (*i_acl != ACL_NOT_CACHED) posix_acl_release(*i_acl); *i_acl = posix_acl_dup(acl); spin_unlock(&inode->i_lock); @@ -161,7 +161,6 @@ ext4_iset_acl(struct inode *inode, struct posix_acl **i_acl, static struct posix_acl * ext4_get_acl(struct inode *inode, int type) { - struct ext4_inode_info *ei = EXT4_I(inode); int name_index; char *value = NULL; struct posix_acl *acl; @@ -172,15 +171,15 @@ ext4_get_acl(struct inode *inode, int type) switch (type) { case ACL_TYPE_ACCESS: - acl = ext4_iget_acl(inode, &ei->i_acl); - if (acl != EXT4_ACL_NOT_CACHED) + acl = ext4_iget_acl(inode, &inode->i_acl); + if (acl != ACL_NOT_CACHED) return acl; name_index = EXT4_XATTR_INDEX_POSIX_ACL_ACCESS; break; case ACL_TYPE_DEFAULT: - acl = ext4_iget_acl(inode, &ei->i_default_acl); - if (acl != EXT4_ACL_NOT_CACHED) + acl = ext4_iget_acl(inode, &inode->i_default_acl); + if (acl != ACL_NOT_CACHED) return acl; name_index = EXT4_XATTR_INDEX_POSIX_ACL_DEFAULT; break; @@ -206,11 +205,11 @@ ext4_get_acl(struct inode *inode, int type) if (!IS_ERR(acl)) { switch (type) { case ACL_TYPE_ACCESS: - ext4_iset_acl(inode, &ei->i_acl, acl); + ext4_iset_acl(inode, &inode->i_acl, acl); break; case ACL_TYPE_DEFAULT: - ext4_iset_acl(inode, &ei->i_default_acl, acl); + ext4_iset_acl(inode, &inode->i_default_acl, acl); break; } } @@ -226,7 +225,6 @@ static int ext4_set_acl(handle_t *handle, struct inode *inode, int type, struct posix_acl *acl) { - struct ext4_inode_info *ei = EXT4_I(inode); int name_index; void *value = NULL; size_t size = 0; @@ -274,11 +272,11 @@ ext4_set_acl(handle_t *handle, struct inode *inode, int type, if (!error) { switch (type) { case ACL_TYPE_ACCESS: - ext4_iset_acl(inode, &ei->i_acl, acl); + ext4_iset_acl(inode, &inode->i_acl, acl); break; case ACL_TYPE_DEFAULT: - ext4_iset_acl(inode, &ei->i_default_acl, acl); + ext4_iset_acl(inode, &inode->i_default_acl, acl); break; } } -- cgit v1.2.3 From 073aaa1b142461d91f83da66db1184d7c1b1edea Mon Sep 17 00:00:00 2001 From: Al Viro Date: Tue, 9 Jun 2009 12:11:54 -0400 Subject: helpers for acl caching + switch to those helpers: get_cached_acl(inode, type), set_cached_acl(inode, type, acl), forget_cached_acl(inode, type). ubifs/xattr.c needed includes reordered, the rest is a plain switchover. Signed-off-by: Al Viro --- fs/ext4/acl.c | 65 +++++++++-------------------------------------------------- 1 file changed, 9 insertions(+), 56 deletions(-) (limited to 'fs/ext4/acl.c') diff --git a/fs/ext4/acl.c b/fs/ext4/acl.c index 0084e3a19d86..f6d8967149ca 100644 --- a/fs/ext4/acl.c +++ b/fs/ext4/acl.c @@ -126,33 +126,6 @@ fail: return ERR_PTR(-EINVAL); } -static inline struct posix_acl * -ext4_iget_acl(struct inode *inode, struct posix_acl **i_acl) -{ - struct posix_acl *acl = ACCESS_ONCE(*i_acl); - - if (acl) { - spin_lock(&inode->i_lock); - acl = *i_acl; - if (acl != ACL_NOT_CACHED) - acl = posix_acl_dup(acl); - spin_unlock(&inode->i_lock); - } - - return acl; -} - -static inline void -ext4_iset_acl(struct inode *inode, struct posix_acl **i_acl, - struct posix_acl *acl) -{ - spin_lock(&inode->i_lock); - if (*i_acl != ACL_NOT_CACHED) - posix_acl_release(*i_acl); - *i_acl = posix_acl_dup(acl); - spin_unlock(&inode->i_lock); -} - /* * Inode operation get_posix_acl(). * @@ -169,23 +142,19 @@ ext4_get_acl(struct inode *inode, int type) if (!test_opt(inode->i_sb, POSIX_ACL)) return NULL; + acl = get_cached_acl(inode, type); + if (acl != ACL_NOT_CACHED) + return acl; + switch (type) { case ACL_TYPE_ACCESS: - acl = ext4_iget_acl(inode, &inode->i_acl); - if (acl != ACL_NOT_CACHED) - return acl; name_index = EXT4_XATTR_INDEX_POSIX_ACL_ACCESS; break; - case ACL_TYPE_DEFAULT: - acl = ext4_iget_acl(inode, &inode->i_default_acl); - if (acl != ACL_NOT_CACHED) - return acl; name_index = EXT4_XATTR_INDEX_POSIX_ACL_DEFAULT; break; - default: - return ERR_PTR(-EINVAL); + BUG(); } retval = ext4_xattr_get(inode, name_index, "", NULL, 0); if (retval > 0) { @@ -202,17 +171,9 @@ ext4_get_acl(struct inode *inode, int type) acl = ERR_PTR(retval); kfree(value); - if (!IS_ERR(acl)) { - switch (type) { - case ACL_TYPE_ACCESS: - ext4_iset_acl(inode, &inode->i_acl, acl); - break; + if (!IS_ERR(acl)) + set_cached_acl(inode, type, acl); - case ACL_TYPE_DEFAULT: - ext4_iset_acl(inode, &inode->i_default_acl, acl); - break; - } - } return acl; } @@ -269,17 +230,9 @@ ext4_set_acl(handle_t *handle, struct inode *inode, int type, value, size, 0); kfree(value); - if (!error) { - switch (type) { - case ACL_TYPE_ACCESS: - ext4_iset_acl(inode, &inode->i_acl, acl); - break; + if (!error) + set_cached_acl(inode, type, acl); - case ACL_TYPE_DEFAULT: - ext4_iset_acl(inode, &inode->i_default_acl, acl); - break; - } - } return error; } -- cgit v1.2.3