Re: [PATCH 1/3] mm: memcg: remote memcg charging for kmem allocations
From: Johannes Weiner <hannes@cmpxchg.org>
Date: 2018-06-19 16:24:29
Also in:
linux-fsdevel, linux-mm, lkml
On Mon, Jun 18, 2018 at 10:13:25PM -0700, Shakeel Butt wrote:
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@@ -248,6 +248,30 @@ static inline void memalloc_noreclaim_restore(unsigned int flags) current->flags = (current->flags & ~PF_MEMALLOC) | flags; } +#ifdef CONFIG_MEMCG +static inline struct mem_cgroup *memalloc_memcg_save(struct mem_cgroup *memcg) +{ + struct mem_cgroup *old_memcg = current->target_memcg; + + current->target_memcg = memcg; + return old_memcg; +} + +static inline void memalloc_memcg_restore(struct mem_cgroup *memcg) +{ + current->target_memcg = memcg; +}
The use_mm() and friends naming scheme would be better here: memalloc_use_memcg(), memalloc_unuse_memcg(), current->active_memcg
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@@ -375,6 +376,27 @@ static __always_inline void kfree_bulk(size_t size, void **p) kmem_cache_free_bulk(NULL, size, p); } +/* + * Calling kmem_cache_alloc_memcg implicitly assumes that the caller wants + * a __GFP_ACCOUNT allocation. However if memcg is NULL then + * kmem_cache_alloc_memcg is same as kmem_cache_alloc. + */ +static __always_inline void *kmem_cache_alloc_memcg(struct kmem_cache *cachep, + gfp_t flags, + struct mem_cgroup *memcg) +{ + struct mem_cgroup *old_memcg; + void *ptr; + + if (!memcg) + return kmem_cache_alloc(cachep, flags); + + old_memcg = memalloc_memcg_save(memcg); + ptr = kmem_cache_alloc(cachep, flags | __GFP_ACCOUNT); + memalloc_memcg_restore(old_memcg); + return ptr;
I'm not a big fan of these functions as an interface because it implies that kmem_cache_alloc() et al wouldn't charge a memcg - but they do, just using current's memcg. It's also a lot of churn to duplicate all the various slab functions. Can you please inline the save/restore (or use/unuse) functions into the callsites? If you make them handle NULL as parameters, it merely adds two bracketing lines around the allocation call in the callsites, which I think would be better to understand - in particular with a comment on why we are charging *that* group instead of current's.
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+static __always_inline struct mem_cgroup *get_mem_cgroup( + struct mem_cgroup *memcg, struct mm_struct *mm) +{ + if (unlikely(memcg)) { + rcu_read_lock(); + if (css_tryget_online(&memcg->css)) { + rcu_read_unlock(); + return memcg; + } + rcu_read_unlock(); + } + return get_mem_cgroup_from_mm(mm); +} + /** * mem_cgroup_iter - iterate over memory cgroup hierarchy * @root: hierarchy root@@ -2260,7 +2274,7 @@ struct kmem_cache *memcg_kmem_get_cache(struct kmem_cache *cachep) if (current->memcg_kmem_skip_account) return cachep; - memcg = get_mem_cgroup_from_mm(current->mm); + memcg = get_mem_cgroup(current->target_memcg, current->mm);
get_mem_cgroup_from_current(), which uses current->active_memcg if set and current->mm->memcg otherwise, would be a nicer abstraction IMO.