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authorVlastimil Babka <vbabka@suse.cz>2021-02-24 23:01:15 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2021-02-25 00:38:27 +0300
commit59450bbc12bee1c4e5dd25e6aa5d6a45a7bd6e81 (patch)
tree5fbebe666e7270e28ca9eddea2f48ca9e5fc9aa9 /mm/slab_common.c
parent7e1fa93deff44677a94dfc323ff629bbf5cf9360 (diff)
downloadlinux-59450bbc12bee1c4e5dd25e6aa5d6a45a7bd6e81.tar.xz
mm, slab, slub: stop taking cpu hotplug lock
SLAB has been using get/put_online_cpus() around creating, destroying and shrinking kmem caches since 95402b382901 ("cpu-hotplug: replace per-subsystem mutexes with get_online_cpus()") in 2008, which is supposed to be replacing a private mutex (cache_chain_mutex, called slab_mutex today) with system-wide mechanism, but in case of SLAB it's in fact used in addition to the existing mutex, without explanation why. SLUB appears to have avoided the cpu hotplug lock initially, but gained it due to common code unification, such as 20cea9683ecc ("mm, sl[aou]b: Move kmem_cache_create mutex handling to common code"). Regardless of the history, checking if the hotplug lock is actually needed today suggests that it's not, and therefore it's better to avoid this system-wide lock and the ordering this imposes wrt other locks (such as slab_mutex). Specifically, in SLAB we have for_each_online_cpu() in do_tune_cpucache() protected by slab_mutex, and cpu hotplug callbacks that also take the slab_mutex, which is also taken by the common slab function that currently also take the hotplug lock. Thus the slab_mutex protection should be sufficient. Also per-cpu array caches are allocated for each possible cpu, so not affected by their online/offline state. In SLUB we have for_each_online_cpu() in functions that show statistics and are already unprotected today, as racing with hotplug is not harmful. Otherwise SLUB relies on percpu allocator. The slub_cpu_dead() hotplug callback takes the slab_mutex. To sum up, this patch removes get/put_online_cpus() calls from slab as it should be safe without further adjustments. Link: https://lkml.kernel.org/r/20210113131634.3671-4-vbabka@suse.cz Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Cc: Christoph Lameter <cl@linux.com> Cc: David Hildenbrand <david@redhat.com> Cc: David Rientjes <rientjes@google.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Pekka Enberg <penberg@kernel.org> Cc: Qian Cai <cai@redhat.com> Cc: Vladimir Davydov <vdavydov.dev@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/slab_common.c')
-rw-r--r--mm/slab_common.c10
1 files changed, 0 insertions, 10 deletions
diff --git a/mm/slab_common.c b/mm/slab_common.c
index d73bea53f759..9633fa1bbbfd 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -309,8 +309,6 @@ kmem_cache_create_usercopy(const char *name,
const char *cache_name;
int err;
- get_online_cpus();
-
mutex_lock(&slab_mutex);
err = kmem_cache_sanity_check(name, size);
@@ -359,8 +357,6 @@ kmem_cache_create_usercopy(const char *name,
out_unlock:
mutex_unlock(&slab_mutex);
- put_online_cpus();
-
if (err) {
if (flags & SLAB_PANIC)
panic("kmem_cache_create: Failed to create slab '%s'. Error %d\n",
@@ -484,8 +480,6 @@ void kmem_cache_destroy(struct kmem_cache *s)
if (unlikely(!s))
return;
- get_online_cpus();
-
mutex_lock(&slab_mutex);
s->refcount--;
@@ -500,8 +494,6 @@ void kmem_cache_destroy(struct kmem_cache *s)
}
out_unlock:
mutex_unlock(&slab_mutex);
-
- put_online_cpus();
}
EXPORT_SYMBOL(kmem_cache_destroy);
@@ -518,12 +510,10 @@ int kmem_cache_shrink(struct kmem_cache *cachep)
{
int ret;
- get_online_cpus();
kasan_cache_shrink(cachep);
ret = __kmem_cache_shrink(cachep);
- put_online_cpus();
return ret;
}
EXPORT_SYMBOL(kmem_cache_shrink);