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Message-ID: <xr937hhuj19a.fsf@ninji.mtv.corp.google.com>
Date: Wed, 06 Oct 2010 17:27:13 -0700
From: Greg Thelen <gthelen@...gle.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Andrea Righi <arighi@...eler.com>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
containers@...ts.osdl.org,
Balbir Singh <balbir@...ux.vnet.ibm.com>,
Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Subject: Re: [PATCH 07/10] memcg: add dirty limits to mem_cgroup
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> writes:
> On Tue, 05 Oct 2010 12:00:17 -0700
> Greg Thelen <gthelen@...gle.com> wrote:
>
>> Andrea Righi <arighi@...eler.com> writes:
>>
>> > On Sun, Oct 03, 2010 at 11:58:02PM -0700, Greg Thelen wrote:
>> >> Extend mem_cgroup to contain dirty page limits. Also add routines
>> >> allowing the kernel to query the dirty usage of a memcg.
>> >>
>> >> These interfaces not used by the kernel yet. A subsequent commit
>> >> will add kernel calls to utilize these new routines.
>> >
>> > A small note below.
>> >
>> >>
>> >> Signed-off-by: Greg Thelen <gthelen@...gle.com>
>> >> Signed-off-by: Andrea Righi <arighi@...eler.com>
>> >> ---
>> >> include/linux/memcontrol.h | 44 +++++++++++
>> >> mm/memcontrol.c | 180 +++++++++++++++++++++++++++++++++++++++++++-
>> >> 2 files changed, 223 insertions(+), 1 deletions(-)
>> >>
>> >> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> >> index 6303da1..dc8952d 100644
>> >> --- a/include/linux/memcontrol.h
>> >> +++ b/include/linux/memcontrol.h
>> >> @@ -19,6 +19,7 @@
>> >>
>> >> #ifndef _LINUX_MEMCONTROL_H
>> >> #define _LINUX_MEMCONTROL_H
>> >> +#include <linux/writeback.h>
>> >> #include <linux/cgroup.h>
>> >> struct mem_cgroup;
>> >> struct page_cgroup;
>> >> @@ -33,6 +34,30 @@ enum mem_cgroup_write_page_stat_item {
>> >> MEMCG_NR_FILE_UNSTABLE_NFS, /* # of NFS unstable pages */
>> >> };
>> >>
>> >> +/* Cgroup memory statistics items exported to the kernel */
>> >> +enum mem_cgroup_read_page_stat_item {
>> >> + MEMCG_NR_DIRTYABLE_PAGES,
>> >> + MEMCG_NR_RECLAIM_PAGES,
>> >> + MEMCG_NR_WRITEBACK,
>> >> + MEMCG_NR_DIRTY_WRITEBACK_PAGES,
>> >> +};
>> >> +
>> >> +/* Dirty memory parameters */
>> >> +struct vm_dirty_param {
>> >> + int dirty_ratio;
>> >> + int dirty_background_ratio;
>> >> + unsigned long dirty_bytes;
>> >> + unsigned long dirty_background_bytes;
>> >> +};
>> >> +
>> >> +static inline void get_global_vm_dirty_param(struct vm_dirty_param *param)
>> >> +{
>> >> + param->dirty_ratio = vm_dirty_ratio;
>> >> + param->dirty_bytes = vm_dirty_bytes;
>> >> + param->dirty_background_ratio = dirty_background_ratio;
>> >> + param->dirty_background_bytes = dirty_background_bytes;
>> >> +}
>> >> +
>> >> extern unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
>> >> struct list_head *dst,
>> >> unsigned long *scanned, int order,
>> >> @@ -145,6 +170,10 @@ static inline void mem_cgroup_dec_page_stat(struct page *page,
>> >> mem_cgroup_update_page_stat(page, idx, -1);
>> >> }
>> >>
>> >> +bool mem_cgroup_has_dirty_limit(void);
>> >> +void get_vm_dirty_param(struct vm_dirty_param *param);
>> >> +s64 mem_cgroup_page_stat(enum mem_cgroup_read_page_stat_item item);
>> >> +
>> >> unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
>> >> gfp_t gfp_mask);
>> >> u64 mem_cgroup_get_limit(struct mem_cgroup *mem);
>> >> @@ -326,6 +355,21 @@ static inline void mem_cgroup_dec_page_stat(struct page *page,
>> >> {
>> >> }
>> >>
>> >> +static inline bool mem_cgroup_has_dirty_limit(void)
>> >> +{
>> >> + return false;
>> >> +}
>> >> +
>> >> +static inline void get_vm_dirty_param(struct vm_dirty_param *param)
>> >> +{
>> >> + get_global_vm_dirty_param(param);
>> >> +}
>> >> +
>> >> +static inline s64 mem_cgroup_page_stat(enum mem_cgroup_read_page_stat_item item)
>> >> +{
>> >> + return -ENOSYS;
>> >> +}
>> >> +
>> >> static inline
>> >> unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
>> >> gfp_t gfp_mask)
>> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> >> index f40839f..6ec2625 100644
>> >> --- a/mm/memcontrol.c
>> >> +++ b/mm/memcontrol.c
>> >> @@ -233,6 +233,10 @@ struct mem_cgroup {
>> >> atomic_t refcnt;
>> >>
>> >> unsigned int swappiness;
>> >> +
>> >> + /* control memory cgroup dirty pages */
>> >> + struct vm_dirty_param dirty_param;
>> >> +
>> >> /* OOM-Killer disable */
>> >> int oom_kill_disable;
>> >>
>> >> @@ -1132,6 +1136,172 @@ static unsigned int get_swappiness(struct mem_cgroup *memcg)
>> >> return swappiness;
>> >> }
>> >>
>> >> +/*
>> >> + * Returns a snapshot of the current dirty limits which is not synchronized with
>> >> + * the routines that change the dirty limits. If this routine races with an
>> >> + * update to the dirty bytes/ratio value, then the caller must handle the case
>> >> + * where both dirty_[background_]_ratio and _bytes are set.
>> >> + */
>> >> +static void __mem_cgroup_get_dirty_param(struct vm_dirty_param *param,
>> >> + struct mem_cgroup *mem)
>> >> +{
>> >> + if (mem && !mem_cgroup_is_root(mem)) {
>> >> + param->dirty_ratio = mem->dirty_param.dirty_ratio;
>> >> + param->dirty_bytes = mem->dirty_param.dirty_bytes;
>> >> + param->dirty_background_ratio =
>> >> + mem->dirty_param.dirty_background_ratio;
>> >> + param->dirty_background_bytes =
>> >> + mem->dirty_param.dirty_background_bytes;
>> >> + } else {
>> >> + get_global_vm_dirty_param(param);
>> >> + }
>> >> +}
>> >> +
>> >> +/*
>> >> + * Get dirty memory parameters of the current memcg or global values (if memory
>> >> + * cgroups are disabled or querying the root cgroup).
>> >> + */
>> >> +void get_vm_dirty_param(struct vm_dirty_param *param)
>> >> +{
>> >> + struct mem_cgroup *memcg;
>> >> +
>> >> + if (mem_cgroup_disabled()) {
>> >> + get_global_vm_dirty_param(param);
>> >> + return;
>> >> + }
>> >> +
>> >> + /*
>> >> + * It's possible that "current" may be moved to other cgroup while we
>> >> + * access cgroup. But precise check is meaningless because the task can
>> >> + * be moved after our access and writeback tends to take long time. At
>> >> + * least, "memcg" will not be freed under rcu_read_lock().
>> >> + */
>> >> + rcu_read_lock();
>> >> + memcg = mem_cgroup_from_task(current);
>> >> + __mem_cgroup_get_dirty_param(param, memcg);
>> >> + rcu_read_unlock();
>> >> +}
>> >> +
>> >> +/*
>> >> + * Check if current memcg has local dirty limits. Return true if the current
>> >> + * memory cgroup has local dirty memory settings.
>> >> + */
>> >> +bool mem_cgroup_has_dirty_limit(void)
>> >> +{
>> >> + struct mem_cgroup *mem;
>> >> +
>> >> + if (mem_cgroup_disabled())
>> >> + return false;
>> >> +
>> >> + mem = mem_cgroup_from_task(current);
>> >> + return mem && !mem_cgroup_is_root(mem);
>> >> +}
>> >
>> > We only check the pointer without dereferencing it, so this is probably
>> > ok, but maybe this is safer:
>> >
>> > bool mem_cgroup_has_dirty_limit(void)
>> > {
>> > struct mem_cgroup *mem;
>> > bool ret;
>> >
>> > if (mem_cgroup_disabled())
>> > return false;
>> >
>> > rcu_read_lock();
>> > mem = mem_cgroup_from_task(current);
>> > ret = mem && !mem_cgroup_is_root(mem);
>> > rcu_read_unlock();
>> >
>> > return ret;
>> > }
>> >
>> > rcu_read_lock() should be held in mem_cgroup_from_task(), otherwise
>> > lockdep could detect this as an error.
>> >
>> > Thanks,
>> > -Andrea
>>
>> Good suggestion. I agree that lockdep might catch this. There are some
>> unrelated debug_locks failures (even without my patches) that I worked
>> around to get lockdep to complain about this one. I applied your
>> suggested fix and lockdep was happy. I will incorporate this fix into
>> the next revision of the patch series.
>>
>
> Hmm, considering other parts, shouldn't we define mem_cgroup_from_task
> as macro ?
>
> Thanks,
> -Kame
Is your motivation to increase performance with the same functionality?
If so, then would a 'static inline' be performance equivalent to a
preprocessor macro yet be safer to use?
Maybe it makes more sense to find a way to perform this check in
mem_cgroup_has_dirty_limit() without needing to grab the rcu lock. I
think this lock grab is unneeded. I am still collecting performance
data, but suspect that this may be making the code slower than it needs
to be.
--
Greg
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