Re: [PATCH 2/2] memcg: reduce usage at change limit

[KAMEZAWA Hiroyuki]

On Tue, 17 Jun 2008 09:16:31 +0530
Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote:

> KAMEZAWA Hiroyuki wrote:
> > Reduce the usage of res_counter at the change of limit.
> > 
> > Changelog v4 -> v5.
> >  - moved "feedback" alogrithm from res_counter to memcg.
> > 
> > Background:
> >  - Now, mem->usage is not reduced at limit change. So, the users will see
> >    usage > limit case in memcg every time. This patch fixes it.
> > 
> >  Before:
> >  - no usage change at setting limit.
> >  - setting limit always returns 0 even if usage can never be less than zero.
> >    (This can happen when memory is locked or there is no swap.)
> >  - This is BUG, I think.
> >  After:
> >  - usage will be less than new limit at limit change.
> >  - set limit returns -EBUSY when the usage cannot be reduced.
> > 
> > 
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> > 
> > ---
> >  Documentation/controllers/memory.txt |    3 -
> >  mm/memcontrol.c                      |   68 ++++++++++++++++++++++++++++-------
> >  2 files changed, 56 insertions(+), 15 deletions(-)
> > 
> > Index: mm-2.6.26-rc5-mm3/mm/memcontrol.c
> > ===================================================================
> > --- mm-2.6.26-rc5-mm3.orig/mm/memcontrol.c
> > +++ mm-2.6.26-rc5-mm3/mm/memcontrol.c
> > @@ -852,18 +852,30 @@ out:
> >  	css_put(&mem->css);
> >  	return ret;
> >  }
> > +/*
> > + * try to set limit and reduce usage if necessary.
> > + * returns 0 at success.
> > + * returns -EBUSY if memory cannot be dropped.
> > + */
> > 
> > -static int mem_cgroup_write_strategy(char *buf, unsigned long long *tmp)
> > +static inline int mem_cgroup_resize_limit(struct cgroup *cont,
> > +					unsigned long long val)
> >  {
> > -	*tmp = memparse(buf, &buf);
> > -	if (*buf != '\0')
> > -		return -EINVAL;
> > +	struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
> > +	int retry_count = 0;
> > +	int progress;
> > 
> > -	/*
> > -	 * Round up the value to the closest page size
> > -	 */
> > -	*tmp = ((*tmp + PAGE_SIZE - 1) >> PAGE_SHIFT) << PAGE_SHIFT;
> > -	return 0;
> > +retry:
> > +	if (!res_counter_set_limit(&memcg->res, val))
> > +		return 0;
> > +	if (retry_count == MEM_CGROUP_RECLAIM_RETRIES)
> > +		return -EBUSY;
> > +
> > +	cond_resched();
> 
> Do we really need this? We do have cond_resched in shrink_page_list(),
> shrink_active_list(), do we need it here as well?
> 
I'd like to add this when adding a busy loop. But ok, will remove.

> > +	progress = try_to_free_mem_cgroup_pages(memcg, GFP_KERNEL);
> > +	if (!progress)
> > +		retry_count++;
> > +	goto retry;
> 
> I don't like upward goto's. Can't we convert this to a nice do {} while or
> while() loop?
> 
Hmm, ok.

I'll repost later, today.

Thanks,
-Kame
> >  }
> > 
> >  static u64 mem_cgroup_read(struct cgroup *cont, struct cftype *cft)
> > @@ -874,11 +886,41 @@ static u64 mem_cgroup_read(struct cgroup
> > 
> >  static ssize_t mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
> >  				struct file *file, const char __user *userbuf,
> > -				size_t nbytes, loff_t *ppos)
> > +				size_t bbytes, loff_t *ppos)
> >  {
> > -	return res_counter_write(&mem_cgroup_from_cont(cont)->res,
> > -				cft->private, userbuf, nbytes, ppos,
> > -				mem_cgroup_write_strategy);
> > +	char *buf, *end;
> > +	unsigned long long val;
> > +	int ret;
> > +
> > +	buf = kmalloc(bbytes + 1, GFP_KERNEL);
> > +	if (!buf)
> > +		return -ENOMEM;
> > +	buf[bbytes] = '\0';
> > +	ret = -EFAULT;
> > +	if (copy_from_user(buf, userbuf, bbytes))
> > +		goto out;
> > +
> > +	ret = -EINVAL;
> > +	strstrip(buf);
> > +	val = memparse(buf, &end);
> > +	if (*end != '\0')
> > +		goto out;
> > +	/* Round to page size */
> > +	val = ((val + PAGE_SIZE - 1) >> PAGE_SHIFT) << PAGE_SHIFT;
> > +
> > +	switch(cft->private) {
> > +	case RES_LIMIT:
> > +		ret = mem_cgroup_resize_limit(cont, val);
> > +		break;
> > +	default:
> > +		ret = -EINVAL;
> > +		goto out;
> > +	}
> > +	if (!ret)
> > +		ret = bbytes;
> > +out:
> > +	kfree(buf);
> > +	return ret;
> >  }
> > 
> >  static int mem_cgroup_reset(struct cgroup *cont, unsigned int event)
> > Index: mm-2.6.26-rc5-mm3/Documentation/controllers/memory.txt
> > ===================================================================
> > --- mm-2.6.26-rc5-mm3.orig/Documentation/controllers/memory.txt
> > +++ mm-2.6.26-rc5-mm3/Documentation/controllers/memory.txt
> > @@ -242,8 +242,7 @@ rmdir() if there are no tasks.
> >  1. Add support for accounting huge pages (as a separate controller)
> >  2. Make per-cgroup scanner reclaim not-shared pages first
> >  3. Teach controller to account for shared-pages
> > -4. Start reclamation when the limit is lowered
> > -5. Start reclamation in the background when the limit is
> > +4. Start reclamation in the background when the limit is
> >     not yet hit but the usage is getting closer
> 
> Except for the minor nits
> 
> Acked-by: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
> 
> -- 
> 	Warm Regards,
> 	Balbir Singh
> 	Linux Technology Center
> 	IBM, ISTL
> 

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/