In general it's unknown in advance if a slab page will contain
accounted objects or not. In order to avoid memory waste, an
obj_cgroup vector is allocated dynamically when a need to account
of a new object arises. Such approach is memory efficient, but
requires an expensive cmpxchg() to set up the memcg/objcgs pointer,
because an allocation can race with a different allocation on another
cpu.
But in some common cases it's known for sure that a slab page will
contain accounted objects: if the page belongs to a slab cache with a
SLAB_ACCOUNT flag set. It includes such popular objects like
vm_area_struct, anon_vma, task_struct, etc.
In such cases we can pre-allocate the objcgs vector and simple assign
it to the page without any atomic operations, because at this early
stage the page is not visible to anyone else.
Signed-off-by: Roman Gushchin <[email protected]>
---
include/linux/memcontrol.h | 14 ++++++++++----
mm/memcontrol.c | 4 ++--
mm/slab.c | 2 +-
mm/slab.h | 14 ++++++++++----
4 files changed, 23 insertions(+), 11 deletions(-)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 20108e426f84..8271f11152e6 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -485,14 +485,20 @@ static inline struct obj_cgroup **page_objcgs_check(struct page *page)
* set_page_objcgs - associate a page with a object cgroups vector
* @page: a pointer to the page struct
* @objcgs: a pointer to the object cgroups vector
+ * @atomic: save the value atomically
*
* Atomically associates a page with a vector of object cgroups.
*/
static inline bool set_page_objcgs(struct page *page,
- struct obj_cgroup **objcgs)
+ struct obj_cgroup **objcgs, bool atomic)
{
- return !cmpxchg(&page->memcg_data, 0, (unsigned long)objcgs |
- MEMCG_DATA_OBJCGS);
+ unsigned long memcg_data = (unsigned long) objcgs | MEMCG_DATA_OBJCGS;
+
+ if (atomic)
+ return !cmpxchg(&page->memcg_data, 0, memcg_data);
+
+ page->memcg_data = memcg_data;
+ return true;
}
#else
static inline struct obj_cgroup **page_objcgs(struct page *page)
@@ -506,7 +512,7 @@ static inline struct obj_cgroup **page_objcgs_check(struct page *page)
}
static inline bool set_page_objcgs(struct page *page,
- struct obj_cgroup **objcgs)
+ struct obj_cgroup **objcgs, bool atomic)
{
return true;
}
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 69a2893a6455..37bffd336235 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2874,7 +2874,7 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg)
#ifdef CONFIG_MEMCG_KMEM
int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
- gfp_t gfp)
+ gfp_t gfp, bool atomic)
{
unsigned int objects = objs_per_slab_page(s, page);
void *vec;
@@ -2884,7 +2884,7 @@ int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
if (!vec)
return -ENOMEM;
- if (!set_page_objcgs(page, vec))
+ if (!set_page_objcgs(page, vec, atomic))
kfree(vec);
else
kmemleak_not_leak(vec);
diff --git a/mm/slab.c b/mm/slab.c
index c0ea4b1c7088..df0299e1d0b9 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1380,7 +1380,7 @@ static struct page *kmem_getpages(struct kmem_cache *cachep, gfp_t flags,
return NULL;
}
- account_slab_page(page, cachep->gfporder, cachep);
+ account_slab_page(page, cachep->gfporder, cachep, flags);
__SetPageSlab(page);
/* Record if ALLOC_NO_WATERMARKS was set when allocating the slab */
if (sk_memalloc_socks() && page_is_pfmemalloc(page))
diff --git a/mm/slab.h b/mm/slab.h
index c73050654b8a..f1d6ba09b630 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -240,7 +240,7 @@ static inline bool kmem_cache_debug_flags(struct kmem_cache *s, slab_flags_t fla
#ifdef CONFIG_MEMCG_KMEM
int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
- gfp_t gfp);
+ gfp_t gfp, bool atomic);
static inline void memcg_free_page_obj_cgroups(struct page *page)
{
@@ -307,7 +307,8 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s,
page = virt_to_head_page(p[i]);
if (!page_objcgs(page) &&
- memcg_alloc_page_obj_cgroups(page, s, flags)) {
+ memcg_alloc_page_obj_cgroups(page, s, flags,
+ true)) {
obj_cgroup_uncharge(objcg, obj_full_size(s));
continue;
}
@@ -371,7 +372,8 @@ static inline struct mem_cgroup *memcg_from_slab_obj(void *ptr)
}
static inline int memcg_alloc_page_obj_cgroups(struct page *page,
- struct kmem_cache *s, gfp_t gfp)
+ struct kmem_cache *s, gfp_t gfp,
+ bool atomic)
{
return 0;
}
@@ -412,8 +414,12 @@ static inline struct kmem_cache *virt_to_cache(const void *obj)
}
static __always_inline void account_slab_page(struct page *page, int order,
- struct kmem_cache *s)
+ struct kmem_cache *s,
+ gfp_t gfp)
{
+ if (memcg_kmem_enabled() && (s->flags & SLAB_ACCOUNT))
+ memcg_alloc_page_obj_cgroups(page, s, gfp, false);
+
mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s),
PAGE_SIZE << order);
}
--
2.26.2
On Tue, 10 Nov 2020 11:57:53 -0800 Roman Gushchin <[email protected]> wrote:
> In general it's unknown in advance if a slab page will contain
> accounted objects or not. In order to avoid memory waste, an
> obj_cgroup vector is allocated dynamically when a need to account
> of a new object arises. Such approach is memory efficient, but
> requires an expensive cmpxchg() to set up the memcg/objcgs pointer,
> because an allocation can race with a different allocation on another
> cpu.
>
> But in some common cases it's known for sure that a slab page will
> contain accounted objects: if the page belongs to a slab cache with a
> SLAB_ACCOUNT flag set. It includes such popular objects like
> vm_area_struct, anon_vma, task_struct, etc.
>
> In such cases we can pre-allocate the objcgs vector and simple assign
> it to the page without any atomic operations, because at this early
> stage the page is not visible to anyone else.
Was there any measurable performance change from this?
On Tue, Nov 10, 2020 at 12:50:08PM -0800, Andrew Morton wrote:
> On Tue, 10 Nov 2020 11:57:53 -0800 Roman Gushchin <[email protected]> wrote:
>
> > In general it's unknown in advance if a slab page will contain
> > accounted objects or not. In order to avoid memory waste, an
> > obj_cgroup vector is allocated dynamically when a need to account
> > of a new object arises. Such approach is memory efficient, but
> > requires an expensive cmpxchg() to set up the memcg/objcgs pointer,
> > because an allocation can race with a different allocation on another
> > cpu.
> >
> > But in some common cases it's known for sure that a slab page will
> > contain accounted objects: if the page belongs to a slab cache with a
> > SLAB_ACCOUNT flag set. It includes such popular objects like
> > vm_area_struct, anon_vma, task_struct, etc.
> >
> > In such cases we can pre-allocate the objcgs vector and simple assign
> > it to the page without any atomic operations, because at this early
> > stage the page is not visible to anyone else.
>
> Was there any measurable performance change from this?
A very simplistic benchmark (allocating 10000000 64-bytes objects in a row)
shows ~15% win. In the real life it seems that most workloads are not very
sensitive to the speed of (accounted) slab allocations.
On Tue, Nov 10, 2020 at 11:57:53AM -0800, Roman Gushchin wrote:
> In general it's unknown in advance if a slab page will contain
> accounted objects or not. In order to avoid memory waste, an
> obj_cgroup vector is allocated dynamically when a need to account
> of a new object arises. Such approach is memory efficient, but
> requires an expensive cmpxchg() to set up the memcg/objcgs pointer,
> because an allocation can race with a different allocation on another
> cpu.
>
> But in some common cases it's known for sure that a slab page will
> contain accounted objects: if the page belongs to a slab cache with a
> SLAB_ACCOUNT flag set. It includes such popular objects like
> vm_area_struct, anon_vma, task_struct, etc.
>
> In such cases we can pre-allocate the objcgs vector and simple assign
> it to the page without any atomic operations, because at this early
> stage the page is not visible to anyone else.
>
> Signed-off-by: Roman Gushchin <[email protected]>
That's a nice optimization!
Some comments inline:
> @@ -485,14 +485,20 @@ static inline struct obj_cgroup **page_objcgs_check(struct page *page)
> * set_page_objcgs - associate a page with a object cgroups vector
> * @page: a pointer to the page struct
> * @objcgs: a pointer to the object cgroups vector
> + * @atomic: save the value atomically
> *
> * Atomically associates a page with a vector of object cgroups.
> */
> static inline bool set_page_objcgs(struct page *page,
> - struct obj_cgroup **objcgs)
> + struct obj_cgroup **objcgs, bool atomic)
bool parameters make callsites pretty hard to understand - unless the
function interface obviously has two modes (read vs write etc.), which
isn't the case here.
> - return !cmpxchg(&page->memcg_data, 0, (unsigned long)objcgs |
> - MEMCG_DATA_OBJCGS);
> + unsigned long memcg_data = (unsigned long) objcgs | MEMCG_DATA_OBJCGS;
> +
> + if (atomic)
> + return !cmpxchg(&page->memcg_data, 0, memcg_data);
> +
> + page->memcg_data = memcg_data;
> + return true;
> }
> #else
> static inline struct obj_cgroup **page_objcgs(struct page *page)
> @@ -506,7 +512,7 @@ static inline struct obj_cgroup **page_objcgs_check(struct page *page)
> }
>
> static inline bool set_page_objcgs(struct page *page,
> - struct obj_cgroup **objcgs)
> + struct obj_cgroup **objcgs, bool atomic)
> {
> return true;
> }
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 69a2893a6455..37bffd336235 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2874,7 +2874,7 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg)
>
> #ifdef CONFIG_MEMCG_KMEM
> int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
> - gfp_t gfp)
> + gfp_t gfp, bool atomic)
> {
> unsigned int objects = objs_per_slab_page(s, page);
> void *vec;
> @@ -2884,7 +2884,7 @@ int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
> if (!vec)
> return -ENOMEM;
>
> - if (!set_page_objcgs(page, vec))
> + if (!set_page_objcgs(page, vec, atomic))
> kfree(vec);
> else
> kmemleak_not_leak(vec);
The life of page->memcg_data and this optimization could use a central
comment somewhere, because it's hard to understand what's going on
from the code alone. This function here seems like a good place?
I don't see a way to eliminate the bool on the allocation function,
but maybe it could be more descriptive. Maybe bool slab_account?
set_page_objcgs() can be inlined at this point. It made some sense to
abstract away the atomics with setter and matching getter, but with a
non-atomic mode, inlining makes things clearer and allows for better
in-place documentation in the sole callsite.
How about something like this?
vec = kcalloc(...);
memcg_data = (unsigned long)vec | MEMCG_DATA_OBJCGS;
/*
* Set up the objcg vector for the page.
*
* When only some objects in a slab are tracked (think GFP_ACCOUNT
* kmalloc allocations), the objcg vector is set up when the first
* tracked object in the slab page is allocated. Multiple concurrent
* slab allocations can race to this, so synchronization is required.
*
* When SLAB_ACCOUNT is set on the cache, however, all objects in the
* slab page will be tracked, and the vector is allocated along with
* the page itself, while it's still exclusive; no atomics necessary.
*/
if (slab_account) {
page->memcg_data = memcg_data;
} else {
if (cmpxchg(&page->memcg_data, 0, memcg_data)) {
/* Somebody else beat us, use their vec */
kfree(vec);
return 0;
}
}
kmemleak_not_leak(vec);
return 0;
On Thu, Nov 12, 2020 at 11:23:03AM -0500, Johannes Weiner wrote:
> On Tue, Nov 10, 2020 at 11:57:53AM -0800, Roman Gushchin wrote:
> > In general it's unknown in advance if a slab page will contain
> > accounted objects or not. In order to avoid memory waste, an
> > obj_cgroup vector is allocated dynamically when a need to account
> > of a new object arises. Such approach is memory efficient, but
> > requires an expensive cmpxchg() to set up the memcg/objcgs pointer,
> > because an allocation can race with a different allocation on another
> > cpu.
> >
> > But in some common cases it's known for sure that a slab page will
> > contain accounted objects: if the page belongs to a slab cache with a
> > SLAB_ACCOUNT flag set. It includes such popular objects like
> > vm_area_struct, anon_vma, task_struct, etc.
> >
> > In such cases we can pre-allocate the objcgs vector and simple assign
> > it to the page without any atomic operations, because at this early
> > stage the page is not visible to anyone else.
> >
> > Signed-off-by: Roman Gushchin <[email protected]>
>
> That's a nice optimization!
>
> Some comments inline:
>
> > @@ -485,14 +485,20 @@ static inline struct obj_cgroup **page_objcgs_check(struct page *page)
> > * set_page_objcgs - associate a page with a object cgroups vector
> > * @page: a pointer to the page struct
> > * @objcgs: a pointer to the object cgroups vector
> > + * @atomic: save the value atomically
> > *
> > * Atomically associates a page with a vector of object cgroups.
> > */
> > static inline bool set_page_objcgs(struct page *page,
> > - struct obj_cgroup **objcgs)
> > + struct obj_cgroup **objcgs, bool atomic)
>
> bool parameters make callsites pretty hard to understand - unless the
> function interface obviously has two modes (read vs write etc.), which
> isn't the case here.
>
> > - return !cmpxchg(&page->memcg_data, 0, (unsigned long)objcgs |
> > - MEMCG_DATA_OBJCGS);
> > + unsigned long memcg_data = (unsigned long) objcgs | MEMCG_DATA_OBJCGS;
> > +
> > + if (atomic)
> > + return !cmpxchg(&page->memcg_data, 0, memcg_data);
> > +
> > + page->memcg_data = memcg_data;
> > + return true;
> > }
> > #else
> > static inline struct obj_cgroup **page_objcgs(struct page *page)
> > @@ -506,7 +512,7 @@ static inline struct obj_cgroup **page_objcgs_check(struct page *page)
> > }
> >
> > static inline bool set_page_objcgs(struct page *page,
> > - struct obj_cgroup **objcgs)
> > + struct obj_cgroup **objcgs, bool atomic)
> > {
> > return true;
> > }
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 69a2893a6455..37bffd336235 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -2874,7 +2874,7 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg)
> >
> > #ifdef CONFIG_MEMCG_KMEM
> > int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
> > - gfp_t gfp)
> > + gfp_t gfp, bool atomic)
> > {
> > unsigned int objects = objs_per_slab_page(s, page);
> > void *vec;
> > @@ -2884,7 +2884,7 @@ int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
> > if (!vec)
> > return -ENOMEM;
> >
> > - if (!set_page_objcgs(page, vec))
> > + if (!set_page_objcgs(page, vec, atomic))
> > kfree(vec);
> > else
> > kmemleak_not_leak(vec);
>
> The life of page->memcg_data and this optimization could use a central
> comment somewhere, because it's hard to understand what's going on
> from the code alone. This function here seems like a good place?
>
> I don't see a way to eliminate the bool on the allocation function,
> but maybe it could be more descriptive. Maybe bool slab_account?
>
> set_page_objcgs() can be inlined at this point. It made some sense to
> abstract away the atomics with setter and matching getter, but with a
> non-atomic mode, inlining makes things clearer and allows for better
> in-place documentation in the sole callsite.
I agree, inlining makes sense here.
I'd prefer not to spill details about SLAB_ACCOUNT into memcg_alloc_page_obj_cgroups().
What's important there is only whether we have an exclusive access to the page or not.
How about the version below?
Thanks!
--
From 8b28d91475d54c552e503e66f169e1e00475c856 Mon Sep 17 00:00:00 2001
From: Roman Gushchin <[email protected]>
Date: Wed, 16 Sep 2020 15:43:48 -0700
Subject: [PATCH v2 2/2] mm: memcg/slab: pre-allocate obj_cgroups for slab
caches with SLAB_ACCOUNT
In general it's unknown in advance if a slab page will contain
accounted objects or not. In order to avoid memory waste, an
obj_cgroup vector is allocated dynamically when a need to account
of a new object arises. Such approach is memory efficient, but
requires an expensive cmpxchg() to set up the memcg/objcgs pointer,
because an allocation can race with a different allocation on another
cpu.
But in some common cases it's known for sure that a slab page will
contain accounted objects: if the page belongs to a slab cache with a
SLAB_ACCOUNT flag set. It includes such popular objects like
vm_area_struct, anon_vma, task_struct, etc.
In such cases we can pre-allocate the objcgs vector and simple assign
it to the page without any atomic operations, because at this early
stage the page is not visible to anyone else.
v2: inline set_page_objcgs() and add some comments, by Johannes
Signed-off-by: Roman Gushchin <[email protected]>
---
include/linux/memcontrol.h | 19 -------------------
mm/memcontrol.c | 23 +++++++++++++++++++----
mm/slab.c | 2 +-
mm/slab.h | 14 ++++++++++----
4 files changed, 30 insertions(+), 28 deletions(-)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 20108e426f84..bfcdcb2d2976 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -481,19 +481,6 @@ static inline struct obj_cgroup **page_objcgs_check(struct page *page)
return (struct obj_cgroup **)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
}
-/*
- * set_page_objcgs - associate a page with a object cgroups vector
- * @page: a pointer to the page struct
- * @objcgs: a pointer to the object cgroups vector
- *
- * Atomically associates a page with a vector of object cgroups.
- */
-static inline bool set_page_objcgs(struct page *page,
- struct obj_cgroup **objcgs)
-{
- return !cmpxchg(&page->memcg_data, 0, (unsigned long)objcgs |
- MEMCG_DATA_OBJCGS);
-}
#else
static inline struct obj_cgroup **page_objcgs(struct page *page)
{
@@ -504,12 +491,6 @@ static inline struct obj_cgroup **page_objcgs_check(struct page *page)
{
return NULL;
}
-
-static inline bool set_page_objcgs(struct page *page,
- struct obj_cgroup **objcgs)
-{
- return true;
-}
#endif
static __always_inline bool memcg_stat_item_in_bytes(int idx)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 69a2893a6455..6ca8c23d7816 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2874,9 +2874,10 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg)
#ifdef CONFIG_MEMCG_KMEM
int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
- gfp_t gfp)
+ gfp_t gfp, bool new_page)
{
unsigned int objects = objs_per_slab_page(s, page);
+ unsigned long memcg_data;
void *vec;
vec = kcalloc_node(objects, sizeof(struct obj_cgroup *), gfp,
@@ -2884,11 +2885,25 @@ int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
if (!vec)
return -ENOMEM;
- if (!set_page_objcgs(page, vec))
+ memcg_data = (unsigned long) vec | MEMCG_DATA_OBJCGS;
+ if (new_page) {
+ /*
+ * If the slab page is brand new and nobody can yet access
+ * it's memcg_data, no synchronization is required and
+ * memcg_data can be simply assigned.
+ */
+ page->memcg_data = memcg_data;
+ } else if (cmpxchg(&page->memcg_data, 0, memcg_data)) {
+ /*
+ * If the slab page is already in use, somebody can allocate
+ * and assign obj_cgroups in parallel. In this case the existing
+ * objcg vector should be reused.
+ */
kfree(vec);
- else
- kmemleak_not_leak(vec);
+ return 0;
+ }
+ kmemleak_not_leak(vec);
return 0;
}
diff --git a/mm/slab.c b/mm/slab.c
index c0ea4b1c7088..df0299e1d0b9 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1380,7 +1380,7 @@ static struct page *kmem_getpages(struct kmem_cache *cachep, gfp_t flags,
return NULL;
}
- account_slab_page(page, cachep->gfporder, cachep);
+ account_slab_page(page, cachep->gfporder, cachep, flags);
__SetPageSlab(page);
/* Record if ALLOC_NO_WATERMARKS was set when allocating the slab */
if (sk_memalloc_socks() && page_is_pfmemalloc(page))
diff --git a/mm/slab.h b/mm/slab.h
index c73050654b8a..59aeb0d9f11b 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -240,7 +240,7 @@ static inline bool kmem_cache_debug_flags(struct kmem_cache *s, slab_flags_t fla
#ifdef CONFIG_MEMCG_KMEM
int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
- gfp_t gfp);
+ gfp_t gfp, bool new_page);
static inline void memcg_free_page_obj_cgroups(struct page *page)
{
@@ -307,7 +307,8 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s,
page = virt_to_head_page(p[i]);
if (!page_objcgs(page) &&
- memcg_alloc_page_obj_cgroups(page, s, flags)) {
+ memcg_alloc_page_obj_cgroups(page, s, flags,
+ false)) {
obj_cgroup_uncharge(objcg, obj_full_size(s));
continue;
}
@@ -371,7 +372,8 @@ static inline struct mem_cgroup *memcg_from_slab_obj(void *ptr)
}
static inline int memcg_alloc_page_obj_cgroups(struct page *page,
- struct kmem_cache *s, gfp_t gfp)
+ struct kmem_cache *s, gfp_t gfp,
+ bool new_page)
{
return 0;
}
@@ -412,8 +414,12 @@ static inline struct kmem_cache *virt_to_cache(const void *obj)
}
static __always_inline void account_slab_page(struct page *page, int order,
- struct kmem_cache *s)
+ struct kmem_cache *s,
+ gfp_t gfp)
{
+ if (memcg_kmem_enabled() && (s->flags & SLAB_ACCOUNT))
+ memcg_alloc_page_obj_cgroups(page, s, gfp, true);
+
mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s),
PAGE_SIZE << order);
}
--
2.26.2
On Thu, 12 Nov 2020 16:19:26 -0800 Roman Gushchin <[email protected]> wrote:
> >From 8b28d91475d54c552e503e66f169e1e00475c856 Mon Sep 17 00:00:00 2001
> From: Roman Gushchin <[email protected]>
> Date: Wed, 16 Sep 2020 15:43:48 -0700
> Subject: [PATCH v2 2/2] mm: memcg/slab: pre-allocate obj_cgroups for slab
> caches with SLAB_ACCOUNT
>
> In general it's unknown in advance if a slab page will contain
> accounted objects or not. In order to avoid memory waste, an
> obj_cgroup vector is allocated dynamically when a need to account
> of a new object arises. Such approach is memory efficient, but
> requires an expensive cmpxchg() to set up the memcg/objcgs pointer,
> because an allocation can race with a different allocation on another
> cpu.
>
> But in some common cases it's known for sure that a slab page will
> contain accounted objects: if the page belongs to a slab cache with a
> SLAB_ACCOUNT flag set. It includes such popular objects like
> vm_area_struct, anon_vma, task_struct, etc.
>
> In such cases we can pre-allocate the objcgs vector and simple assign
> it to the page without any atomic operations, because at this early
> stage the page is not visible to anyone else.
>
> v2: inline set_page_objcgs() and add some comments, by Johannes
Had me confused! I was looking for the inlined function
set_page_objcgs(). I think "open-code" is a better term here than
"inline".
Here's the -fix:
From: Roman Gushchin <[email protected]>
Subject: mm-memcg-slab-pre-allocate-obj_cgroups-for-slab-caches-with-slab_account-v2
open-code set_page_objcgs() and add some comments, by Johannes
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Roman Gushchin <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Shakeel Butt <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---
include/linux/memcontrol.h | 25 -------------------------
mm/memcontrol.c | 23 +++++++++++++++++++----
mm/slab.h | 8 ++++----
3 files changed, 23 insertions(+), 33 deletions(-)
--- a/include/linux/memcontrol.h~mm-memcg-slab-pre-allocate-obj_cgroups-for-slab-caches-with-slab_account-v2
+++ a/include/linux/memcontrol.h
@@ -480,25 +480,6 @@ static inline struct obj_cgroup **page_o
return (struct obj_cgroup **)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
}
-/*
- * set_page_objcgs - associate a page with a object cgroups vector
- * @page: a pointer to the page struct
- * @objcgs: a pointer to the object cgroups vector
- * @atomic: save the value atomically
- *
- * Atomically associates a page with a vector of object cgroups.
- */
-static inline bool set_page_objcgs(struct page *page,
- struct obj_cgroup **objcgs, bool atomic)
-{
- unsigned long memcg_data = (unsigned long) objcgs | MEMCG_DATA_OBJCGS;
-
- if (atomic)
- return !cmpxchg(&page->memcg_data, 0, memcg_data);
-
- page->memcg_data = memcg_data;
- return true;
-}
#else
static inline struct obj_cgroup **page_objcgs(struct page *page)
{
@@ -509,12 +490,6 @@ static inline struct obj_cgroup **page_o
{
return NULL;
}
-
-static inline bool set_page_objcgs(struct page *page,
- struct obj_cgroup **objcgs, bool atomic)
-{
- return true;
-}
#endif
static __always_inline bool memcg_stat_item_in_bytes(int idx)
--- a/mm/memcontrol.c~mm-memcg-slab-pre-allocate-obj_cgroups-for-slab-caches-with-slab_account-v2
+++ a/mm/memcontrol.c
@@ -2879,9 +2879,10 @@ static void commit_charge(struct page *p
#ifdef CONFIG_MEMCG_KMEM
int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
- gfp_t gfp, bool atomic)
+ gfp_t gfp, bool new_page)
{
unsigned int objects = objs_per_slab_page(s, page);
+ unsigned long memcg_data;
void *vec;
vec = kcalloc_node(objects, sizeof(struct obj_cgroup *), gfp,
@@ -2889,11 +2890,25 @@ int memcg_alloc_page_obj_cgroups(struct
if (!vec)
return -ENOMEM;
- if (!set_page_objcgs(page, vec, atomic))
+ memcg_data = (unsigned long) vec | MEMCG_DATA_OBJCGS;
+ if (new_page) {
+ /*
+ * If the slab page is brand new and nobody can yet access
+ * it's memcg_data, no synchronization is required and
+ * memcg_data can be simply assigned.
+ */
+ page->memcg_data = memcg_data;
+ } else if (cmpxchg(&page->memcg_data, 0, memcg_data)) {
+ /*
+ * If the slab page is already in use, somebody can allocate
+ * and assign obj_cgroups in parallel. In this case the existing
+ * objcg vector should be reused.
+ */
kfree(vec);
- else
- kmemleak_not_leak(vec);
+ return 0;
+ }
+ kmemleak_not_leak(vec);
return 0;
}
--- a/mm/slab.h~mm-memcg-slab-pre-allocate-obj_cgroups-for-slab-caches-with-slab_account-v2
+++ a/mm/slab.h
@@ -240,7 +240,7 @@ static inline bool kmem_cache_debug_flag
#ifdef CONFIG_MEMCG_KMEM
int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
- gfp_t gfp, bool atomic);
+ gfp_t gfp, bool new_page);
static inline void memcg_free_page_obj_cgroups(struct page *page)
{
@@ -308,7 +308,7 @@ static inline void memcg_slab_post_alloc
if (!page_objcgs(page) &&
memcg_alloc_page_obj_cgroups(page, s, flags,
- true)) {
+ false)) {
obj_cgroup_uncharge(objcg, obj_full_size(s));
continue;
}
@@ -373,7 +373,7 @@ static inline struct mem_cgroup *memcg_f
static inline int memcg_alloc_page_obj_cgroups(struct page *page,
struct kmem_cache *s, gfp_t gfp,
- bool atomic)
+ bool new_page)
{
return 0;
}
@@ -418,7 +418,7 @@ static __always_inline void account_slab
gfp_t gfp)
{
if (memcg_kmem_enabled() && (s->flags & SLAB_ACCOUNT))
- memcg_alloc_page_obj_cgroups(page, s, gfp, false);
+ memcg_alloc_page_obj_cgroups(page, s, gfp, true);
mod_node_page_state(page_pgdat(page), cache_vmstat_idx(s),
PAGE_SIZE << order);
_
On Thu, Nov 12, 2020 at 05:12:39PM -0800, Andrew Morton wrote:
> On Thu, 12 Nov 2020 16:19:26 -0800 Roman Gushchin <[email protected]> wrote:
>
> > >From 8b28d91475d54c552e503e66f169e1e00475c856 Mon Sep 17 00:00:00 2001
> > From: Roman Gushchin <[email protected]>
> > Date: Wed, 16 Sep 2020 15:43:48 -0700
> > Subject: [PATCH v2 2/2] mm: memcg/slab: pre-allocate obj_cgroups for slab
> > caches with SLAB_ACCOUNT
> >
> > In general it's unknown in advance if a slab page will contain
> > accounted objects or not. In order to avoid memory waste, an
> > obj_cgroup vector is allocated dynamically when a need to account
> > of a new object arises. Such approach is memory efficient, but
> > requires an expensive cmpxchg() to set up the memcg/objcgs pointer,
> > because an allocation can race with a different allocation on another
> > cpu.
> >
> > But in some common cases it's known for sure that a slab page will
> > contain accounted objects: if the page belongs to a slab cache with a
> > SLAB_ACCOUNT flag set. It includes such popular objects like
> > vm_area_struct, anon_vma, task_struct, etc.
> >
> > In such cases we can pre-allocate the objcgs vector and simple assign
> > it to the page without any atomic operations, because at this early
> > stage the page is not visible to anyone else.
> >
> > v2: inline set_page_objcgs() and add some comments, by Johannes
>
> Had me confused! I was looking for the inlined function
> set_page_objcgs(). I think "open-code" is a better term here than
> "inline".
Sorry for the confusion! And thanks for picking up the new version!
Roman
On Thu, Nov 12, 2020 at 05:12:39PM -0800, Andrew Morton wrote:
> On Thu, 12 Nov 2020 16:19:26 -0800 Roman Gushchin <[email protected]> wrote:
>
> > >From 8b28d91475d54c552e503e66f169e1e00475c856 Mon Sep 17 00:00:00 2001
> > From: Roman Gushchin <[email protected]>
> > Date: Wed, 16 Sep 2020 15:43:48 -0700
> > Subject: [PATCH v2 2/2] mm: memcg/slab: pre-allocate obj_cgroups for slab
> > caches with SLAB_ACCOUNT
> >
> > In general it's unknown in advance if a slab page will contain
> > accounted objects or not. In order to avoid memory waste, an
> > obj_cgroup vector is allocated dynamically when a need to account
> > of a new object arises. Such approach is memory efficient, but
> > requires an expensive cmpxchg() to set up the memcg/objcgs pointer,
> > because an allocation can race with a different allocation on another
> > cpu.
> >
> > But in some common cases it's known for sure that a slab page will
> > contain accounted objects: if the page belongs to a slab cache with a
> > SLAB_ACCOUNT flag set. It includes such popular objects like
> > vm_area_struct, anon_vma, task_struct, etc.
> >
> > In such cases we can pre-allocate the objcgs vector and simple assign
> > it to the page without any atomic operations, because at this early
> > stage the page is not visible to anyone else.
> >
> > v2: inline set_page_objcgs() and add some comments, by Johannes
>
> Had me confused! I was looking for the inlined function
> set_page_objcgs(). I think "open-code" is a better term here than
> "inline".
>
> Here's the -fix:
>
> From: Roman Gushchin <[email protected]>
> Subject: mm-memcg-slab-pre-allocate-obj_cgroups-for-slab-caches-with-slab_account-v2
>
> open-code set_page_objcgs() and add some comments, by Johannes
>
> Link: https://lkml.kernel.org/r/[email protected]
> Signed-off-by: Roman Gushchin <[email protected]>
> Cc: Christoph Lameter <[email protected]>
> Cc: Johannes Weiner <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: Shakeel Butt <[email protected]>
> Signed-off-by: Andrew Morton <[email protected]>
Thanks! For the combined patch:
Acked-by: Johannes Weiner <[email protected]>
On Thu, Nov 12, 2020 at 4:19 PM Roman Gushchin <[email protected]> wrote:
>
[snip]
>
> From 8b28d91475d54c552e503e66f169e1e00475c856 Mon Sep 17 00:00:00 2001
> From: Roman Gushchin <[email protected]>
> Date: Wed, 16 Sep 2020 15:43:48 -0700
> Subject: [PATCH v2 2/2] mm: memcg/slab: pre-allocate obj_cgroups for slab
> caches with SLAB_ACCOUNT
>
> In general it's unknown in advance if a slab page will contain
> accounted objects or not. In order to avoid memory waste, an
> obj_cgroup vector is allocated dynamically when a need to account
> of a new object arises. Such approach is memory efficient, but
> requires an expensive cmpxchg() to set up the memcg/objcgs pointer,
> because an allocation can race with a different allocation on another
> cpu.
>
> But in some common cases it's known for sure that a slab page will
> contain accounted objects: if the page belongs to a slab cache with a
> SLAB_ACCOUNT flag set. It includes such popular objects like
> vm_area_struct, anon_vma, task_struct, etc.
>
> In such cases we can pre-allocate the objcgs vector and simple assign
> it to the page without any atomic operations, because at this early
> stage the page is not visible to anyone else.
>
> v2: inline set_page_objcgs() and add some comments, by Johannes
>
> Signed-off-by: Roman Gushchin <[email protected]>
[snip]
>
> static __always_inline void account_slab_page(struct page *page, int order,
> - struct kmem_cache *s)
> + struct kmem_cache *s,
> + gfp_t gfp)
> {
> + if (memcg_kmem_enabled() && (s->flags & SLAB_ACCOUNT))
> + memcg_alloc_page_obj_cgroups(page, s, gfp, true);
> +
I was wondering why not add (gfp & __GFP_ACCOUNT) check as well but it
seems like for that some additional plumbing is required.
Anyways:
Reviewed-by: Shakeel Butt <[email protected]>
On Tue, Nov 17, 2020 at 09:42:53AM -0800, Shakeel Butt wrote:
> On Thu, Nov 12, 2020 at 4:19 PM Roman Gushchin <[email protected]> wrote:
> >
> [snip]
> >
> > From 8b28d91475d54c552e503e66f169e1e00475c856 Mon Sep 17 00:00:00 2001
> > From: Roman Gushchin <[email protected]>
> > Date: Wed, 16 Sep 2020 15:43:48 -0700
> > Subject: [PATCH v2 2/2] mm: memcg/slab: pre-allocate obj_cgroups for slab
> > caches with SLAB_ACCOUNT
> >
> > In general it's unknown in advance if a slab page will contain
> > accounted objects or not. In order to avoid memory waste, an
> > obj_cgroup vector is allocated dynamically when a need to account
> > of a new object arises. Such approach is memory efficient, but
> > requires an expensive cmpxchg() to set up the memcg/objcgs pointer,
> > because an allocation can race with a different allocation on another
> > cpu.
> >
> > But in some common cases it's known for sure that a slab page will
> > contain accounted objects: if the page belongs to a slab cache with a
> > SLAB_ACCOUNT flag set. It includes such popular objects like
> > vm_area_struct, anon_vma, task_struct, etc.
> >
> > In such cases we can pre-allocate the objcgs vector and simple assign
> > it to the page without any atomic operations, because at this early
> > stage the page is not visible to anyone else.
> >
> > v2: inline set_page_objcgs() and add some comments, by Johannes
> >
> > Signed-off-by: Roman Gushchin <[email protected]>
> [snip]
> >
> > static __always_inline void account_slab_page(struct page *page, int order,
> > - struct kmem_cache *s)
> > + struct kmem_cache *s,
> > + gfp_t gfp)
> > {
> > + if (memcg_kmem_enabled() && (s->flags & SLAB_ACCOUNT))
> > + memcg_alloc_page_obj_cgroups(page, s, gfp, true);
> > +
>
> I was wondering why not add (gfp & __GFP_ACCOUNT) check as well but it
> seems like for that some additional plumbing is required.
Yes, it's doable, but requires passing another argument through the whole stack.
>
> Anyways:
>
> Reviewed-by: Shakeel Butt <[email protected]>
Thank you!