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Message-ID: <20140923180920.GC29528@dhcp22.suse.cz>
Date: Tue, 23 Sep 2014 20:09:20 +0200
From: Michal Hocko <mhocko@...e.cz>
To: Vladimir Davydov <vdavydov@...allels.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Johannes Weiner <hannes@...xchg.org>,
Christoph Lameter <cl@...ux.com>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [PATCH v2 3/3] memcg: move memcg_update_cache_size to
slab_common.c
On Mon 22-09-14 20:00:46, Vladimir Davydov wrote:
> While growing per memcg caches arrays, we jump between memcontrol.c and
> slab_common.c in a weird way:
>
> memcg_alloc_cache_id - memcontrol.c
> memcg_update_all_caches - slab_common.c
> memcg_update_cache_size - memcontrol.c
>
> There's absolutely no reason why memcg_update_cache_size can't live on
> the slab's side though. So let's move it there and settle it comfortably
> amid per-memcg cache allocation functions.
>
> Besides, this patch cleans this function up a bit, removing all the
> useless comments from it, and renames it to memcg_update_cache_params to
> conform to memcg_alloc/free_cache_params, which we already have in
> slab_common.c.
>
> Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>
I found new_params->memcg_caches[i] = ... style of initialization easier
to read and understand than memcpy. This is not something to block
this cleanup but I would be happier to have the array style back ;)
Acked-by: Michal Hocko <mhocko@...e.cz>
> ---
> include/linux/memcontrol.h | 1 -
> mm/memcontrol.c | 49 --------------------------------------------
> mm/slab_common.c | 30 +++++++++++++++++++++++++--
> 3 files changed, 28 insertions(+), 52 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 4d17242eeff7..19df5d857411 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -440,7 +440,6 @@ void __memcg_kmem_uncharge_pages(struct page *page, int order);
>
> int memcg_cache_id(struct mem_cgroup *memcg);
>
> -int memcg_update_cache_size(struct kmem_cache *s, int num_groups);
> void memcg_update_array_size(int num_groups);
>
> struct kmem_cache *
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 55d131645b45..1ec22bf380d0 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2944,55 +2944,6 @@ void memcg_update_array_size(int num)
> memcg_limited_groups_array_size = num;
> }
>
> -int memcg_update_cache_size(struct kmem_cache *s, int num_groups)
> -{
> - struct memcg_cache_params *cur_params = s->memcg_params;
> - struct memcg_cache_params *new_params;
> - size_t size;
> - int i;
> -
> - VM_BUG_ON(!is_root_cache(s));
> -
> - size = num_groups * sizeof(void *);
> - size += offsetof(struct memcg_cache_params, memcg_caches);
> -
> - new_params = kzalloc(size, GFP_KERNEL);
> - if (!new_params)
> - return -ENOMEM;
> -
> - new_params->is_root_cache = true;
> -
> - /*
> - * There is the chance it will be bigger than
> - * memcg_limited_groups_array_size, if we failed an allocation
> - * in a cache, in which case all caches updated before it, will
> - * have a bigger array.
> - *
> - * But if that is the case, the data after
> - * memcg_limited_groups_array_size is certainly unused
> - */
> - for (i = 0; i < memcg_limited_groups_array_size; i++) {
> - if (!cur_params->memcg_caches[i])
> - continue;
> - new_params->memcg_caches[i] =
> - cur_params->memcg_caches[i];
> - }
> -
> - /*
> - * Ideally, we would wait until all caches succeed, and only
> - * then free the old one. But this is not worth the extra
> - * pointer per-cache we'd have to have for this.
> - *
> - * It is not a big deal if some caches are left with a size
> - * bigger than the others. And all updates will reset this
> - * anyway.
> - */
> - rcu_assign_pointer(s->memcg_params, new_params);
> - if (cur_params)
> - kfree_rcu(cur_params, rcu_head);
> - return 0;
> -}
> -
> static void memcg_register_cache(struct mem_cgroup *memcg,
> struct kmem_cache *root_cache)
> {
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 9c29ba792368..800314e2a075 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -120,6 +120,33 @@ static void memcg_free_cache_params(struct kmem_cache *s)
> kfree(s->memcg_params);
> }
>
> +static int memcg_update_cache_params(struct kmem_cache *s, int num_memcgs)
> +{
> + int size;
> + struct memcg_cache_params *new_params, *cur_params;
> +
> + BUG_ON(!is_root_cache(s));
> +
> + size = offsetof(struct memcg_cache_params, memcg_caches);
> + size += num_memcgs * sizeof(void *);
> +
> + new_params = kzalloc(size, GFP_KERNEL);
> + if (!new_params)
> + return -ENOMEM;
> +
> + cur_params = s->memcg_params;
> + memcpy(new_params->memcg_caches, cur_params->memcg_caches,
> + memcg_limited_groups_array_size * sizeof(void *));
> +
> + new_params->is_root_cache = true;
> +
> + rcu_assign_pointer(s->memcg_params, new_params);
> + if (cur_params)
> + kfree_rcu(cur_params, rcu_head);
> +
> + return 0;
> +}
> +
> int memcg_update_all_caches(int num_memcgs)
> {
> struct kmem_cache *s;
> @@ -130,9 +157,8 @@ int memcg_update_all_caches(int num_memcgs)
> if (!is_root_cache(s))
> continue;
>
> - ret = memcg_update_cache_size(s, num_memcgs);
> + ret = memcg_update_cache_params(s, num_memcgs);
> /*
> - * See comment in memcontrol.c, memcg_update_cache_size:
> * Instead of freeing the memory, we'll just leave the caches
> * up to this point in an updated state.
> */
> --
> 1.7.10.4
>
--
Michal Hocko
SUSE Labs
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