Commit 2e9bd483 authored by Roman Gushchin's avatar Roman Gushchin Committed by Linus Torvalds
Browse files

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.

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.

[guro@fb.com: open-code set_page_objcgs() and add some comments, by Johannes]
  Link: https://lkml.kernel.org/r/20201113001926.GA2934489@carbon.dhcp.thefacebook.com
[akpm@linux-foundation.org: fix it for mm-slub-call-account_slab_page-after-slab-page-initialization-fix.patch]

Link: https://lkml.kernel.org/r/20201110195753.530157-2-guro@fb.com


Signed-off-by: default avatarRoman Gushchin <guro@fb.com>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Reviewed-by: default avatarShakeel Butt <shakeelb@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent cad8320b

include/linux/memcontrol.h

+0 −19
Original line number Diff line number Diff line
@@ -475,19 +475,6 @@ 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)

{
@@ -498,12 +485,6 @@ 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)

mm/memcontrol.c

+19 −4
Original line number Diff line number Diff line
@@ -2935,9 +2935,10 @@ 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,
@@ -2945,11 +2946,25 @@ 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;

}

mm/slab.c

+1 −1
Original line number Diff line number Diff line
@@ -1379,7 +1379,7 @@ 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))

mm/slab.h

+10 −4
Original line number Diff line number Diff line
@@ -238,7 +238,7 @@ 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)

{
@@ -315,7 +315,8 @@ 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;

			}
@@ -379,7 +380,8 @@ 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;

}
@@ -420,8 +422,12 @@ 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);

}

mm/slub.c

+1 −1
Original line number Diff line number Diff line
@@ -1785,7 +1785,7 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node) 


	page->objects = oo_objects(oo);



	account_slab_page(page, oo_order(oo), s);

	account_slab_page(page, oo_order(oo), s, flags);



	page->slab_cache = s;

	__SetPageSlab(page);