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From: Johannes Weiner <hannes@cmpxchg.org>
To: Roman Gushchin <guro@fb.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@kernel.org>,
	linux-mm@kvack.org, kernel-team@fb.com,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 06/19] mm: memcg/slab: obj_cgroup API
Date: Thu, 7 May 2020 17:03:14 -0400	[thread overview]
Message-ID: <20200507210314.GD161043@cmpxchg.org> (raw)
In-Reply-To: <20200422204708.2176080-7-guro@fb.com>

On Wed, Apr 22, 2020 at 01:46:55PM -0700, Roman Gushchin wrote:
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -257,6 +257,78 @@ struct cgroup_subsys_state *vmpressure_to_css(struct vmpressure *vmpr)
>  }
>  
>  #ifdef CONFIG_MEMCG_KMEM
> +extern spinlock_t css_set_lock;
> +
> +static void obj_cgroup_release(struct percpu_ref *ref)
> +{
> +	struct obj_cgroup *objcg = container_of(ref, struct obj_cgroup, refcnt);
> +	struct mem_cgroup *memcg;
> +	unsigned int nr_bytes;
> +	unsigned int nr_pages;
> +	unsigned long flags;
> +
> +	nr_bytes = atomic_read(&objcg->nr_charged_bytes);
> +	WARN_ON_ONCE(nr_bytes & (PAGE_SIZE - 1));
> +	nr_pages = nr_bytes >> PAGE_SHIFT;

What guarantees that we don't have a partial page in there at this
point? I guess any outstanding allocations would pin the objcg, so
when it's released all objects have been freed.

But if that's true, how can we have full pages remaining in there now?

> @@ -2723,6 +2820,30 @@ struct mem_cgroup *mem_cgroup_from_obj(void *p)
>  	return page->mem_cgroup;
>  }
>  
> +__always_inline struct obj_cgroup *get_obj_cgroup_from_current(void)
> +{
> +	struct obj_cgroup *objcg = NULL;
> +	struct mem_cgroup *memcg;
> +
> +	if (unlikely(!current->mm))
> +		return NULL;
> +
> +	rcu_read_lock();
> +	if (unlikely(current->active_memcg))
> +		memcg = rcu_dereference(current->active_memcg);
> +	else
> +		memcg = mem_cgroup_from_task(current);
> +
> +	for (; memcg != root_mem_cgroup; memcg = parent_mem_cgroup(memcg)) {
> +		objcg = rcu_dereference(memcg->objcg);
> +		if (objcg && obj_cgroup_tryget(objcg))
> +			break;
> +	}
> +	rcu_read_unlock();
> +
> +	return objcg;
> +}

Thanks for moving this here from one of the later patches, it helps
understanding the life cycle of obj_cgroup better.

> +int obj_cgroup_charge(struct obj_cgroup *objcg, gfp_t gfp, size_t size)
> +{
> +	struct mem_cgroup *memcg;
> +	unsigned int nr_pages, nr_bytes;
> +	int ret;
> +
> +	if (consume_obj_stock(objcg, size))
> +		return 0;
> +
> +	rcu_read_lock();
> +	memcg = obj_cgroup_memcg(objcg);
> +	css_get(&memcg->css);
> +	rcu_read_unlock();
> +
> +	nr_pages = size >> PAGE_SHIFT;
> +	nr_bytes = size & (PAGE_SIZE - 1);
> +
> +	if (nr_bytes)
> +		nr_pages += 1;
> +
> +	ret = __memcg_kmem_charge(memcg, gfp, nr_pages);

If consume_obj_stock() fails because some other memcg is cached,
should this try to consume the partial page in objcg->nr_charged_bytes
before getting more pages?

> +	if (!ret && nr_bytes)
> +		refill_obj_stock(objcg, PAGE_SIZE - nr_bytes);

This will put the cgroup into the cache if the allocation resulted in
a partially free page.

But if this was a page allocation, we may have objcg->nr_cache_bytes
from a previous subpage allocation that we should probably put back
into the stock.

It's not a common case, I'm just trying to understand what
objcg->nr_cache_bytes holds and when it does so.

The rest of this patch looks good to me!


  reply	other threads:[~2020-05-07 21:03 UTC|newest]

Thread overview: 84+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-22 20:46 [PATCH v3 00/19] The new cgroup slab memory controller Roman Gushchin
2020-04-22 20:46 ` [PATCH v3 01/19] mm: memcg: factor out memcg- and lruvec-level changes out of __mod_lruvec_state() Roman Gushchin
2020-05-07 20:33   ` Johannes Weiner
2020-05-20 10:49   ` Vlastimil Babka
2020-04-22 20:46 ` [PATCH v3 02/19] mm: memcg: prepare for byte-sized vmstat items Roman Gushchin
2020-05-07 20:34   ` Johannes Weiner
2020-05-20 11:31   ` Vlastimil Babka
2020-05-20 11:36     ` Vlastimil Babka
2020-04-22 20:46 ` [PATCH v3 03/19] mm: memcg: convert vmstat slab counters to bytes Roman Gushchin
2020-05-07 20:41   ` Johannes Weiner
2020-05-20 12:25   ` Vlastimil Babka
2020-05-20 19:26     ` Roman Gushchin
2020-05-21  9:57       ` Vlastimil Babka
2020-05-21 21:14         ` Roman Gushchin
2020-04-22 20:46 ` [PATCH v3 04/19] mm: slub: implement SLUB version of obj_to_index() Roman Gushchin
2020-04-22 23:52   ` Christopher Lameter
2020-04-23  0:05     ` Roman Gushchin
2020-04-25  2:10       ` Christopher Lameter
2020-04-25  2:46         ` Roman Gushchin
2020-04-27 16:21           ` Christopher Lameter
2020-04-27 16:46             ` Roman Gushchin
2020-04-28 17:06               ` Roman Gushchin
2020-04-28 17:45               ` Johannes Weiner
2020-04-30 16:29               ` Christopher Lameter
2020-04-30 17:15                 ` Roman Gushchin
2020-05-02 23:54                   ` Christopher Lameter
2020-05-04 18:29                     ` Roman Gushchin
2020-05-08 21:35                       ` Christopher Lameter
2020-05-13  0:57                         ` Roman Gushchin
2020-05-15 21:45                           ` Christopher Lameter
2020-05-15 22:12                             ` Roman Gushchin
2020-05-20  9:51                           ` Vlastimil Babka
2020-05-20 20:57                             ` Roman Gushchin
2020-05-15 20:02                         ` Roman Gushchin
2020-04-23 21:01     ` Roman Gushchin
2020-04-25  2:10       ` Christopher Lameter
2020-05-20 13:51   ` Vlastimil Babka
2020-05-20 21:00     ` Roman Gushchin
2020-05-21 11:01       ` Vlastimil Babka
2020-05-21 21:06         ` Roman Gushchin
2020-04-22 20:46 ` [PATCH v3 05/19] mm: memcontrol: decouple reference counting from page accounting Roman Gushchin
2020-04-22 20:46 ` [PATCH v3 06/19] mm: memcg/slab: obj_cgroup API Roman Gushchin
2020-05-07 21:03   ` Johannes Weiner [this message]
2020-05-07 22:26     ` Roman Gushchin
2020-05-12 22:56       ` Johannes Weiner
2020-05-15 22:01         ` Roman Gushchin
2020-04-22 20:46 ` [PATCH v3 07/19] mm: memcg/slab: allocate obj_cgroups for non-root slab pages Roman Gushchin
2020-04-23 20:20   ` Roman Gushchin
2020-05-22 18:27   ` Vlastimil Babka
2020-05-23  1:32     ` Roman Gushchin
2020-05-26 17:50     ` Roman Gushchin
2020-05-25 14:46   ` Vlastimil Babka
2020-04-22 20:46 ` [PATCH v3 08/19] mm: memcg/slab: save obj_cgroup for non-root slab objects Roman Gushchin
2020-05-25 15:07   ` Vlastimil Babka
2020-05-26 17:53     ` Roman Gushchin
2020-05-27 11:03       ` Vlastimil Babka
2020-04-22 20:46 ` [PATCH v3 09/19] mm: memcg/slab: charge individual slab objects instead of pages Roman Gushchin
2020-05-25 16:10   ` Vlastimil Babka
2020-05-26 18:04     ` Roman Gushchin
2020-04-22 20:46 ` [PATCH v3 10/19] mm: memcg/slab: deprecate memory.kmem.slabinfo Roman Gushchin
2020-05-07 21:05   ` Johannes Weiner
2020-04-22 20:47 ` [PATCH v3 11/19] mm: memcg/slab: move memcg_kmem_bypass() to memcontrol.h Roman Gushchin
2020-05-25 17:03   ` Vlastimil Babka
2020-04-22 20:47 ` [PATCH v3 12/19] mm: memcg/slab: use a single set of kmem_caches for all accounted allocations Roman Gushchin
2020-05-26 10:12   ` Vlastimil Babka
2020-04-22 20:47 ` [PATCH v3 13/19] mm: memcg/slab: simplify memcg cache creation Roman Gushchin
2020-05-26 10:31   ` Vlastimil Babka
2020-04-22 20:47 ` [PATCH v3 14/19] mm: memcg/slab: deprecate memcg_kmem_get_cache() Roman Gushchin
2020-05-26 10:34   ` Vlastimil Babka
2020-04-22 20:47 ` [PATCH v3 15/19] mm: memcg/slab: deprecate slab_root_caches Roman Gushchin
2020-05-26 10:52   ` Vlastimil Babka
2020-05-26 18:50     ` Roman Gushchin
2020-04-22 20:47 ` [PATCH v3 16/19] mm: memcg/slab: remove redundant check in memcg_accumulate_slabinfo() Roman Gushchin
2020-05-26 11:31   ` Vlastimil Babka
2020-04-22 20:47 ` [PATCH v3 17/19] mm: memcg/slab: use a single set of kmem_caches for all allocations Roman Gushchin
2020-05-26 14:55   ` Vlastimil Babka
2020-05-27  8:35     ` Jesper Dangaard Brouer
2020-04-22 20:47 ` [PATCH v3 18/19] kselftests: cgroup: add kernel memory accounting tests Roman Gushchin
2020-05-26 15:24   ` Vlastimil Babka
2020-05-26 15:45     ` Roman Gushchin
2020-05-27 17:00       ` Vlastimil Babka
2020-05-27 20:45         ` Roman Gushchin
2020-04-22 20:47 ` [PATCH v3 19/19] tools/cgroup: add memcg_slabinfo.py tool Roman Gushchin
2020-05-05 15:59   ` Tejun Heo

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