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SubjectRe: [PATCH 2/2] memcg: reduce usage at change limit
On Tue, 17 Jun 2008 09:16:31 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> 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@jp.fujitsu.com>
> >
> > ---
> > 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@linux.vnet.ibm.com>
>
> --
> Warm Regards,
> Balbir Singh
> Linux Technology Center
> IBM, ISTL
>



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