From: Konstantin Khlebnikov khlebnikov@yandex-team.ru
Currently unregistering sysctl table does not prune its dentries. Stale dentries could slowdown sysctl operations significantly.
For example, command:
# for i in {1..100000} ; do unshare -n -- sysctl -a &> /dev/null ; done creates a millions of stale denties around sysctls of loopback interface:
# sysctl fs.dentry-state fs.dentry-state = 25812579 24724135 45 0 0 0
All of them have matching names thus lookup have to scan though whole hash chain and call d_compare (proc_sys_compare) which checks them under system-wide spinlock (sysctl_lock).
# time sysctl -a > /dev/null real 1m12.806s user 0m0.016s sys 1m12.400s
Currently only memory reclaimer could remove this garbage. But without significant memory pressure this never happens.
This patch collects sysctl inodes into list on sysctl table header and prunes all their dentries once that table unregisters.
Konstantin Khlebnikov khlebnikov@yandex-team.ru writes:
On 10.02.2017 10:47, Al Viro wrote:
how about >> the matching stats *after* that patch?
dcache size doesn't grow endlessly, so stats are fine
# sysctl fs.dentry-state fs.dentry-state = 92712 58376 45 0 0 0
# time sysctl -a &>/dev/null
real 0m0.013s user 0m0.004s sys 0m0.008s
Signed-off-by: Konstantin Khlebnikov khlebnikov@yandex-team.ru Suggested-by: Al Viro viro@zeniv.linux.org.uk Signed-off-by: Eric W. Biederman ebiederm@xmission.com --- fs/proc/inode.c | 3 ++- fs/proc/internal.h | 7 ++++-- fs/proc/proc_sysctl.c | 59 ++++++++++++++++++++++++++++++++++++-------------- include/linux/sysctl.h | 1 + 4 files changed, 51 insertions(+), 19 deletions(-)
diff --git a/fs/proc/inode.c b/fs/proc/inode.c index e69ebe6..c2afe39 100644 --- a/fs/proc/inode.c +++ b/fs/proc/inode.c @@ -43,10 +43,11 @@ static void proc_evict_inode(struct inode *inode) de = PDE(inode); if (de) pde_put(de); + head = PROC_I(inode)->sysctl; if (head) { RCU_INIT_POINTER(PROC_I(inode)->sysctl, NULL); - sysctl_head_put(head); + proc_sys_evict_inode(inode, head); } }
diff --git a/fs/proc/internal.h b/fs/proc/internal.h index 5378441..7aad3f6 100644 --- a/fs/proc/internal.h +++ b/fs/proc/internal.h @@ -65,6 +65,7 @@ struct proc_inode { struct proc_dir_entry *pde; struct ctl_table_header *sysctl; struct ctl_table *sysctl_entry; + struct list_head sysctl_inodes; const struct proc_ns_operations *ns_ops; struct inode vfs_inode; }; @@ -249,10 +250,12 @@ extern void proc_thread_self_init(void); */ #ifdef CONFIG_PROC_SYSCTL extern int proc_sys_init(void); -extern void sysctl_head_put(struct ctl_table_header *); +extern void proc_sys_evict_inode(struct inode *inode, + struct ctl_table_header *head); #else static inline void proc_sys_init(void) { } -static inline void sysctl_head_put(struct ctl_table_header *head) { } +static inline void proc_sys_evict_inode(struct inode *inode, + struct ctl_table_header *head) { } #endif
/* diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c index 847f234..1f91765 100644 --- a/fs/proc/proc_sysctl.c +++ b/fs/proc/proc_sysctl.c @@ -190,6 +190,7 @@ static void init_header(struct ctl_table_header *head, head->set = set; head->parent = NULL; head->node = node; + INIT_LIST_HEAD(&head->inodes); if (node) { struct ctl_table *entry; for (entry = table; entry->procname; entry++, node++) @@ -259,6 +260,29 @@ static void unuse_table(struct ctl_table_header *p) complete(p->unregistering); }
+/* called under sysctl_lock */ +static void proc_sys_prune_dcache(struct ctl_table_header *head) +{ + struct inode *inode, *prev = NULL; + struct proc_inode *ei; + + list_for_each_entry(ei, &head->inodes, sysctl_inodes) { + inode = igrab(&ei->vfs_inode); + if (inode) { + spin_unlock(&sysctl_lock); + iput(prev); + prev = inode; + d_prune_aliases(inode); + spin_lock(&sysctl_lock); + } + } + if (prev) { + spin_unlock(&sysctl_lock); + iput(prev); + spin_lock(&sysctl_lock); + } +} + /* called under sysctl_lock, will reacquire if has to wait */ static void start_unregistering(struct ctl_table_header *p) { @@ -278,27 +302,17 @@ static void start_unregistering(struct ctl_table_header *p) p->unregistering = ERR_PTR(-EINVAL); } /* + * Prune dentries for unregistered sysctls: namespaced sysctls + * can have duplicate names and contaminate dcache very badly. + */ + proc_sys_prune_dcache(p); + /* * do not remove from the list until nobody holds it; walking the * list in do_sysctl() relies on that. */ erase_header(p); }
-static void sysctl_head_get(struct ctl_table_header *head) -{ - spin_lock(&sysctl_lock); - head->count++; - spin_unlock(&sysctl_lock); -} - -void sysctl_head_put(struct ctl_table_header *head) -{ - spin_lock(&sysctl_lock); - if (!--head->count) - kfree_rcu(head, rcu); - spin_unlock(&sysctl_lock); -} - static struct ctl_table_header *sysctl_head_grab(struct ctl_table_header *head) { BUG_ON(!head); @@ -440,11 +454,15 @@ static struct inode *proc_sys_make_inode(struct super_block *sb,
inode->i_ino = get_next_ino();
- sysctl_head_get(head); ei = PROC_I(inode); ei->sysctl = head; ei->sysctl_entry = table;
+ spin_lock(&sysctl_lock); + list_add(&ei->sysctl_inodes, &head->inodes); + head->count++; + spin_unlock(&sysctl_lock); + inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode); inode->i_mode = table->mode; if (!S_ISDIR(table->mode)) { @@ -466,6 +484,15 @@ static struct inode *proc_sys_make_inode(struct super_block *sb, return inode; }
+void proc_sys_evict_inode(struct inode *inode, struct ctl_table_header *head) +{ + spin_lock(&sysctl_lock); + list_del(&PROC_I(inode)->sysctl_inodes); + if (!--head->count) + kfree_rcu(head, rcu); + spin_unlock(&sysctl_lock); +} + static struct ctl_table_header *grab_header(struct inode *inode) { struct ctl_table_header *head = PROC_I(inode)->sysctl; diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h index adf4e51..b7e8204 100644 --- a/include/linux/sysctl.h +++ b/include/linux/sysctl.h @@ -143,6 +143,7 @@ struct ctl_table_header struct ctl_table_set *set; struct ctl_dir *parent; struct ctl_node *node; + struct list_head inodes; /* head for proc_inode->sysctl_inodes */ };
struct ctl_dir {