The patch titled
Subject: fs/epoll: use a per-cpu counter for user's watches count
has been removed from the -mm tree. Its filename was
fs-epoll-use-a-per-cpu-counter-for-users-watches-count.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Nicholas Piggin <npiggin@xxxxxxxxx>
Subject: fs/epoll: use a per-cpu counter for user's watches count
This counter tracks the number of watches a user has, to compare against
the 'max_user_watches' limit. This causes a scalability bottleneck on
SPECjbb2015 on large systems as there is only one user. Changing to a
per-cpu counter increases throughput of the benchmark by about 30% on a
16-socket, > 1000 thread system.
[rdunlap@xxxxxxxxxxxxx: fix build errors in kernel/user.c when CONFIG_EPOLL=n]
[npiggin@xxxxxxxxx: move ifdefs into wrapper functions, slightly improve panic message]
Link: https://lkml.kernel.org/r/1628051945.fens3r99ox.astroid@xxxxxxxxx
[akpm@xxxxxxxxxxxxxxxxxxxx: tweak user_epoll_alloc(), per Guenter]
Link: https://lkml.kernel.org/r/20210804191421.GA1900577@xxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20210802032013.2751916-1-npiggin@xxxxxxxxx
Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
Reported-by: Anton Blanchard <anton@xxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/eventpoll.c | 18 ++++++++++--------
include/linux/sched/user.h | 3 ++-
kernel/user.c | 25 +++++++++++++++++++++++++
3 files changed, 37 insertions(+), 9 deletions(-)
--- a/fs/eventpoll.c~fs-epoll-use-a-per-cpu-counter-for-users-watches-count
+++ a/fs/eventpoll.c
@@ -723,7 +723,7 @@ static int ep_remove(struct eventpoll *e
*/
call_rcu(&epi->rcu, epi_rcu_free);
- atomic_long_dec(&ep->user->epoll_watches);
+ percpu_counter_dec(&ep->user->epoll_watches);
return 0;
}
@@ -1439,7 +1439,6 @@ static int ep_insert(struct eventpoll *e
{
int error, pwake = 0;
__poll_t revents;
- long user_watches;
struct epitem *epi;
struct ep_pqueue epq;
struct eventpoll *tep = NULL;
@@ -1449,11 +1448,15 @@ static int ep_insert(struct eventpoll *e
lockdep_assert_irqs_enabled();
- user_watches = atomic_long_read(&ep->user->epoll_watches);
- if (unlikely(user_watches >= max_user_watches))
+ if (unlikely(percpu_counter_compare(&ep->user->epoll_watches,
+ max_user_watches) >= 0))
return -ENOSPC;
- if (!(epi = kmem_cache_zalloc(epi_cache, GFP_KERNEL)))
+ percpu_counter_inc(&ep->user->epoll_watches);
+
+ if (!(epi = kmem_cache_zalloc(epi_cache, GFP_KERNEL))) {
+ percpu_counter_dec(&ep->user->epoll_watches);
return -ENOMEM;
+ }
/* Item initialization follow here ... */
INIT_LIST_HEAD(&epi->rdllink);
@@ -1466,17 +1469,16 @@ static int ep_insert(struct eventpoll *e
mutex_lock_nested(&tep->mtx, 1);
/* Add the current item to the list of active epoll hook for this file */
if (unlikely(attach_epitem(tfile, epi) < 0)) {
- kmem_cache_free(epi_cache, epi);
if (tep)
mutex_unlock(&tep->mtx);
+ kmem_cache_free(epi_cache, epi);
+ percpu_counter_dec(&ep->user->epoll_watches);
return -ENOMEM;
}
if (full_check && !tep)
list_file(tfile);
- atomic_long_inc(&ep->user->epoll_watches);
-
/*
* Add the current item to the RB tree. All RB tree operations are
* protected by "mtx", and ep_insert() is called with "mtx" held.
--- a/include/linux/sched/user.h~fs-epoll-use-a-per-cpu-counter-for-users-watches-count
+++ a/include/linux/sched/user.h
@@ -4,6 +4,7 @@
#include <linux/uidgid.h>
#include <linux/atomic.h>
+#include <linux/percpu_counter.h>
#include <linux/refcount.h>
#include <linux/ratelimit.h>
@@ -13,7 +14,7 @@
struct user_struct {
refcount_t __count; /* reference count */
#ifdef CONFIG_EPOLL
- atomic_long_t epoll_watches; /* The number of file descriptors currently watched */
+ struct percpu_counter epoll_watches; /* The number of file descriptors currently watched */
#endif
unsigned long unix_inflight; /* How many files in flight in unix sockets */
atomic_long_t pipe_bufs; /* how many pages are allocated in pipe buffers */
--- a/kernel/user.c~fs-epoll-use-a-per-cpu-counter-for-users-watches-count
+++ a/kernel/user.c
@@ -129,6 +129,22 @@ static struct user_struct *uid_hash_find
return NULL;
}
+static int user_epoll_alloc(struct user_struct *up)
+{
+#ifdef CONFIG_EPOLL
+ return percpu_counter_init(&up->epoll_watches, 0, GFP_KERNEL);
+#else
+ return 0;
+#endif
+}
+
+static void user_epoll_free(struct user_struct *up)
+{
+#ifdef CONFIG_EPOLL
+ percpu_counter_destroy(&up->epoll_watches);
+#endif
+}
+
/* IRQs are disabled and uidhash_lock is held upon function entry.
* IRQ state (as stored in flags) is restored and uidhash_lock released
* upon function exit.
@@ -138,6 +154,7 @@ static void free_user(struct user_struct
{
uid_hash_remove(up);
spin_unlock_irqrestore(&uidhash_lock, flags);
+ user_epoll_free(up);
kmem_cache_free(uid_cachep, up);
}
@@ -185,6 +202,10 @@ struct user_struct *alloc_uid(kuid_t uid
new->uid = uid;
refcount_set(&new->__count, 1);
+ if (user_epoll_alloc(new)) {
+ kmem_cache_free(uid_cachep, new);
+ return NULL;
+ }
ratelimit_state_init(&new->ratelimit, HZ, 100);
ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE);
@@ -195,6 +216,7 @@ struct user_struct *alloc_uid(kuid_t uid
spin_lock_irq(&uidhash_lock);
up = uid_hash_find(uid, hashent);
if (up) {
+ user_epoll_free(new);
kmem_cache_free(uid_cachep, new);
} else {
uid_hash_insert(new, hashent);
@@ -216,6 +238,9 @@ static int __init uid_cache_init(void)
for(n = 0; n < UIDHASH_SZ; ++n)
INIT_HLIST_HEAD(uidhash_table + n);
+ if (user_epoll_alloc(&root_user))
+ panic("root_user epoll percpu counter alloc failed");
+
/* Insert the root user immediately (init already runs as root) */
spin_lock_irq(&uidhash_lock);
uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
_
Patches currently in -mm which might be from npiggin@xxxxxxxxx are
lazy-tlb-introduce-lazy-mm-refcount-helper-functions.patch
lazy-tlb-allow-lazy-tlb-mm-refcounting-to-be-configurable.patch
lazy-tlb-shoot-lazies-a-non-refcounting-lazy-tlb-option.patch
powerpc-64s-enable-mmu_lazy_tlb_shootdown.patch
