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Date: Tue, 13 Apr 2021 08:56:26 +0200
From: Michal Hocko <mhocko@...e.com>
To: ultrachin@....com
Cc: linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
hannes@...xchg.org, vdavydov.dev@...il.com, linux-mm@...ck.org,
cgroups@...r.kernel.org, Chen Xiaoguang <xiaoggchen@...cent.com>,
Chen He <heddchen@...cent.com>
Subject: Re: [PATCH] mm: optimize memory allocation
On Mon 12-04-21 15:49:53, ultrachin@....com wrote:
> From: Chen Xiaoguang <xiaoggchen@...cent.com>
>
> Check memory cgroup limit before allocating real memory. This may
> improve performance especially in slow path when memory allocation
> exceeds cgroup limitation.
I would be really curious about any actual numbers because I have really
hard times to see scenarios when this would lead to an improvement.
Effectitelly only non-oom allocations would benefit theoretically (e.g.
atomic or GFP_NORETRY etc). All others will trigger the memcg oom killer
to help forward progress.
Besides that I really dislike kmem and LRU pages to be handled
differently so for that reason
Nacked-by: Michal Hocko <mhocko@...e.com>
If the optimization really can be provent then the patch would require
to be much more invasive.
> Signed-off-by: Chen Xiaoguang <xiaoggchen@...cent.com>
> Signed-off-by: Chen He <heddchen@...cent.com>
> ---
> include/linux/memcontrol.h | 30 ++++++++++++++++++++++--------
> mm/memcontrol.c | 34 ++++++++++++++++------------------
> mm/page_alloc.c | 24 +++++++++++++++++-------
> 3 files changed, 55 insertions(+), 33 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 0c04d39..59bb3ba 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -1583,8 +1583,9 @@ static inline void memcg_set_shrinker_bit(struct mem_cgroup *memcg,
> #endif
>
> #ifdef CONFIG_MEMCG_KMEM
> -int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order);
> -void __memcg_kmem_uncharge_page(struct page *page, int order);
> +int __memcg_kmem_charge_page(struct mem_cgroup *memcg, gfp_t gfp, int order);
> +void __memcg_kmem_uncharge_page(struct page *page, int order,
> + struct mem_cgroup *memcg);
>
> struct obj_cgroup *get_obj_cgroup_from_current(void);
>
> @@ -1610,18 +1611,30 @@ static inline bool memcg_kmem_enabled(void)
> return static_branch_likely(&memcg_kmem_enabled_key);
> }
>
> +extern struct mem_cgroup *get_mem_cgroup_from_current(void);
> +
> static inline int memcg_kmem_charge_page(struct page *page, gfp_t gfp,
> int order)
> {
> - if (memcg_kmem_enabled())
> - return __memcg_kmem_charge_page(page, gfp, order);
> - return 0;
> + struct mem_cgroup *memcg;
> + int ret = 0;
> +
> + memcg = get_mem_cgroup_from_current();
> + if (memcg && memcg_kmem_enabled() && !mem_cgroup_is_root(memcg)) {
> + ret = __memcg_kmem_charge_page(memcg, gfp, order);
> + if (!ret) {
> + page->memcg_data = (unsigned long)memcg | MEMCG_DATA_KMEM;
> + return 0;
> + }
> + css_put(&memcg->css);
> + }
> + return ret;
> }
>
> static inline void memcg_kmem_uncharge_page(struct page *page, int order)
> {
> if (memcg_kmem_enabled())
> - __memcg_kmem_uncharge_page(page, order);
> + __memcg_kmem_uncharge_page(page, order, NULL);
> }
>
> /*
> @@ -1647,13 +1660,14 @@ static inline void memcg_kmem_uncharge_page(struct page *page, int order)
> {
> }
>
> -static inline int __memcg_kmem_charge_page(struct page *page, gfp_t gfp,
> +static inline int __memcg_kmem_charge_page(struct mem_cgroup *memcg, gfp_t gfp,
> int order)
> {
> return 0;
> }
>
> -static inline void __memcg_kmem_uncharge_page(struct page *page, int order)
> +static inline void __memcg_kmem_uncharge_page(struct page *page, int order,
> + struct mem_cgroup *memcg)
> {
> }
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e064ac0d..8df57b7 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1085,7 +1085,7 @@ static __always_inline bool memcg_kmem_bypass(void)
> /**
> * If active memcg is set, do not fallback to current->mm->memcg.
> */
> -static __always_inline struct mem_cgroup *get_mem_cgroup_from_current(void)
> +struct mem_cgroup *get_mem_cgroup_from_current(void)
> {
> if (memcg_kmem_bypass())
> return NULL;
> @@ -3113,21 +3113,11 @@ static void __memcg_kmem_uncharge(struct mem_cgroup *memcg, unsigned int nr_page
> *
> * Returns 0 on success, an error code on failure.
> */
> -int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order)
> +int __memcg_kmem_charge_page(struct mem_cgroup *memcg, gfp_t gfp, int order)
> {
> - struct mem_cgroup *memcg;
> - int ret = 0;
> + int ret;
>
> - memcg = get_mem_cgroup_from_current();
> - if (memcg && !mem_cgroup_is_root(memcg)) {
> - ret = __memcg_kmem_charge(memcg, gfp, 1 << order);
> - if (!ret) {
> - page->memcg_data = (unsigned long)memcg |
> - MEMCG_DATA_KMEM;
> - return 0;
> - }
> - css_put(&memcg->css);
> - }
> + ret = __memcg_kmem_charge(memcg, gfp, 1 << order);
> return ret;
> }
>
> @@ -3136,17 +3126,25 @@ int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order)
> * @page: page to uncharge
> * @order: allocation order
> */
> -void __memcg_kmem_uncharge_page(struct page *page, int order)
> +void __memcg_kmem_uncharge_page(struct page *page, int order,
> + struct mem_cgroup *memcg_in)
> {
> - struct mem_cgroup *memcg = page_memcg(page);
> + struct mem_cgroup *memcg;
> unsigned int nr_pages = 1 << order;
>
> + if (page)
> + memcg = page_memcg(page);
> + else
> + memcg = memcg_in;
> +
> if (!memcg)
> return;
>
> - VM_BUG_ON_PAGE(mem_cgroup_is_root(memcg), page);
> + if (page)
> + VM_BUG_ON_PAGE(mem_cgroup_is_root(memcg), page);
> __memcg_kmem_uncharge(memcg, nr_pages);
> - page->memcg_data = 0;
> + if (page)
> + page->memcg_data = 0;
> css_put(&memcg->css);
> }
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index cfc7287..c3d1d0c 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1230,7 +1230,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
> * Untie memcg state and reset page's owner
> */
> if (memcg_kmem_enabled() && PageMemcgKmem(page))
> - __memcg_kmem_uncharge_page(page, order);
> + __memcg_kmem_uncharge_page(page, order, NULL);
> reset_page_owner(page, order);
> return false;
> }
> @@ -1260,7 +1260,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
> if (PageMappingFlags(page))
> page->mapping = NULL;
> if (memcg_kmem_enabled() && PageMemcgKmem(page))
> - __memcg_kmem_uncharge_page(page, order);
> + __memcg_kmem_uncharge_page(page, order, NULL);
> if (check_free)
> bad += check_free_page(page);
> if (bad)
> @@ -4976,6 +4976,8 @@ struct page *
> unsigned int alloc_flags = ALLOC_WMARK_LOW;
> gfp_t alloc_mask; /* The gfp_t that was actually used for allocation */
> struct alloc_context ac = { };
> + struct mem_cgroup *memcg;
> + bool charged = false;
>
> /*
> * There are several places where we assume that the order value is sane
> @@ -4987,6 +4989,15 @@ struct page *
> }
>
> gfp_mask &= gfp_allowed_mask;
> + memcg = get_mem_cgroup_from_current();
> + if (memcg && memcg_kmem_enabled() && (gfp_mask & __GFP_ACCOUNT) &&
> + !mem_cgroup_is_root(memcg)) {
> + if (unlikely(__memcg_kmem_charge_page(memcg, gfp_mask, order) != 0)) {
> + css_put(&memcg->css);
> + return NULL;
> + }
> + charged = true;
> + }
> alloc_mask = gfp_mask;
> if (!prepare_alloc_pages(gfp_mask, order, preferred_nid, nodemask, &ac, &alloc_mask, &alloc_flags))
> return NULL;
> @@ -5020,11 +5031,10 @@ struct page *
> page = __alloc_pages_slowpath(alloc_mask, order, &ac);
>
> out:
> - if (memcg_kmem_enabled() && (gfp_mask & __GFP_ACCOUNT) && page &&
> - unlikely(__memcg_kmem_charge_page(page, gfp_mask, order) != 0)) {
> - __free_pages(page, order);
> - page = NULL;
> - }
> + if (page && charged)
> + page->memcg_data = (unsigned long)memcg | MEMCG_DATA_KMEM;
> + else if (charged)
> + __memcg_kmem_uncharge_page(NULL, order, memcg);
>
> trace_mm_page_alloc(page, order, alloc_mask, ac.migratetype);
>
> --
> 1.8.3.1
>
--
Michal Hocko
SUSE Labs
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