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Message-ID: <20141015152128.GH23547@dhcp22.suse.cz>
Date: Wed, 15 Oct 2014 17:21:28 +0200
From: Michal Hocko <mhocko@...e.cz>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Vladimir Davydov <vdavydov@...allels.com>, linux-mm@...ck.org,
cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 3/5] mm: memcontrol: remove obsolete kmemcg pinning tricks
On Tue 14-10-14 12:20:35, Johannes Weiner wrote:
> As charges now pin the css explicitely, there is no more need for
> kmemcg to acquire a proxy reference for outstanding pages during
> offlining, or maintain state to identify such "dead" groups.
>
> This was the last user of the uncharge functions' return values, so
> remove them as well.
>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> Reviewed-by: Vladimir Davydov <vdavydov@...allels.com>
Acked-by: Michal Hocko <mhocko@...e.cz>
> ---
> include/linux/page_counter.h | 4 +--
> mm/memcontrol.c | 74 +-------------------------------------------
> mm/page_counter.c | 23 +++-----------
> 3 files changed, 7 insertions(+), 94 deletions(-)
>
> diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h
> index d92d18949474..a878ef61d073 100644
> --- a/include/linux/page_counter.h
> +++ b/include/linux/page_counter.h
> @@ -32,12 +32,12 @@ static inline unsigned long page_counter_read(struct page_counter *counter)
> return atomic_long_read(&counter->count);
> }
>
> -int page_counter_cancel(struct page_counter *counter, unsigned long nr_pages);
> +void page_counter_cancel(struct page_counter *counter, unsigned long nr_pages);
> void page_counter_charge(struct page_counter *counter, unsigned long nr_pages);
> int page_counter_try_charge(struct page_counter *counter,
> unsigned long nr_pages,
> struct page_counter **fail);
> -int page_counter_uncharge(struct page_counter *counter, unsigned long nr_pages);
> +void page_counter_uncharge(struct page_counter *counter, unsigned long nr_pages);
> int page_counter_limit(struct page_counter *counter, unsigned long limit);
> int page_counter_memparse(const char *buf, unsigned long *nr_pages);
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a3feead6be15..7551e12f8ff7 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -369,7 +369,6 @@ struct mem_cgroup {
> /* internal only representation about the status of kmem accounting. */
> enum {
> KMEM_ACCOUNTED_ACTIVE, /* accounted by this cgroup itself */
> - KMEM_ACCOUNTED_DEAD, /* dead memcg with pending kmem charges */
> };
>
> #ifdef CONFIG_MEMCG_KMEM
> @@ -383,22 +382,6 @@ static bool memcg_kmem_is_active(struct mem_cgroup *memcg)
> return test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_account_flags);
> }
>
> -static void memcg_kmem_mark_dead(struct mem_cgroup *memcg)
> -{
> - /*
> - * Our caller must use css_get() first, because memcg_uncharge_kmem()
> - * will call css_put() if it sees the memcg is dead.
> - */
> - smp_wmb();
> - if (test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_account_flags))
> - set_bit(KMEM_ACCOUNTED_DEAD, &memcg->kmem_account_flags);
> -}
> -
> -static bool memcg_kmem_test_and_clear_dead(struct mem_cgroup *memcg)
> -{
> - return test_and_clear_bit(KMEM_ACCOUNTED_DEAD,
> - &memcg->kmem_account_flags);
> -}
> #endif
>
> /* Stuffs for move charges at task migration. */
> @@ -2741,22 +2724,7 @@ static void memcg_uncharge_kmem(struct mem_cgroup *memcg,
> if (do_swap_account)
> page_counter_uncharge(&memcg->memsw, nr_pages);
>
> - /* Not down to 0 */
> - if (page_counter_uncharge(&memcg->kmem, nr_pages)) {
> - css_put_many(&memcg->css, nr_pages);
> - return;
> - }
> -
> - /*
> - * Releases a reference taken in kmem_cgroup_css_offline in case
> - * this last uncharge is racing with the offlining code or it is
> - * outliving the memcg existence.
> - *
> - * The memory barrier imposed by test&clear is paired with the
> - * explicit one in memcg_kmem_mark_dead().
> - */
> - if (memcg_kmem_test_and_clear_dead(memcg))
> - css_put(&memcg->css);
> + page_counter_uncharge(&memcg->kmem, nr_pages);
>
> css_put_many(&memcg->css, nr_pages);
> }
> @@ -4740,40 +4708,6 @@ static void memcg_destroy_kmem(struct mem_cgroup *memcg)
> {
> mem_cgroup_sockets_destroy(memcg);
> }
> -
> -static void kmem_cgroup_css_offline(struct mem_cgroup *memcg)
> -{
> - if (!memcg_kmem_is_active(memcg))
> - return;
> -
> - /*
> - * kmem charges can outlive the cgroup. In the case of slab
> - * pages, for instance, a page contain objects from various
> - * processes. As we prevent from taking a reference for every
> - * such allocation we have to be careful when doing uncharge
> - * (see memcg_uncharge_kmem) and here during offlining.
> - *
> - * The idea is that that only the _last_ uncharge which sees
> - * the dead memcg will drop the last reference. An additional
> - * reference is taken here before the group is marked dead
> - * which is then paired with css_put during uncharge resp. here.
> - *
> - * Although this might sound strange as this path is called from
> - * css_offline() when the referencemight have dropped down to 0 and
> - * shouldn't be incremented anymore (css_tryget_online() would
> - * fail) we do not have other options because of the kmem
> - * allocations lifetime.
> - */
> - css_get(&memcg->css);
> -
> - memcg_kmem_mark_dead(memcg);
> -
> - if (page_counter_read(&memcg->kmem))
> - return;
> -
> - if (memcg_kmem_test_and_clear_dead(memcg))
> - css_put(&memcg->css);
> -}
> #else
> static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
> {
> @@ -4783,10 +4717,6 @@ static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
> static void memcg_destroy_kmem(struct mem_cgroup *memcg)
> {
> }
> -
> -static void kmem_cgroup_css_offline(struct mem_cgroup *memcg)
> -{
> -}
> #endif
>
> /*
> @@ -5390,8 +5320,6 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
> }
> spin_unlock(&memcg->event_list_lock);
>
> - kmem_cgroup_css_offline(memcg);
> -
> /*
> * This requires that offlining is serialized. Right now that is
> * guaranteed because css_killed_work_fn() holds the cgroup_mutex.
> diff --git a/mm/page_counter.c b/mm/page_counter.c
> index fc4990c6bb5b..71a0e92e7051 100644
> --- a/mm/page_counter.c
> +++ b/mm/page_counter.c
> @@ -12,19 +12,14 @@
> * page_counter_cancel - take pages out of the local counter
> * @counter: counter
> * @nr_pages: number of pages to cancel
> - *
> - * Returns whether there are remaining pages in the counter.
> */
> -int page_counter_cancel(struct page_counter *counter, unsigned long nr_pages)
> +void page_counter_cancel(struct page_counter *counter, unsigned long nr_pages)
> {
> long new;
>
> new = atomic_long_sub_return(nr_pages, &counter->count);
> -
> /* More uncharges than charges? */
> WARN_ON_ONCE(new < 0);
> -
> - return new > 0;
> }
>
> /**
> @@ -113,23 +108,13 @@ failed:
> * page_counter_uncharge - hierarchically uncharge pages
> * @counter: counter
> * @nr_pages: number of pages to uncharge
> - *
> - * Returns whether there are remaining charges in @counter.
> */
> -int page_counter_uncharge(struct page_counter *counter, unsigned long nr_pages)
> +void page_counter_uncharge(struct page_counter *counter, unsigned long nr_pages)
> {
> struct page_counter *c;
> - int ret = 1;
>
> - for (c = counter; c; c = c->parent) {
> - int remainder;
> -
> - remainder = page_counter_cancel(c, nr_pages);
> - if (c == counter && !remainder)
> - ret = 0;
> - }
> -
> - return ret;
> + for (c = counter; c; c = c->parent)
> + page_counter_cancel(c, nr_pages);
> }
>
> /**
> --
> 2.1.2
>
--
Michal Hocko
SUSE Labs
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