Re: [RFC][PATCH] memcg: add valid check at allocating or freeing memory

[Balbir Singh <balbir@linux.vnet.ibm.com>]

* nishimura@mxp.nes.nec.co.jp <nishimura@mxp.nes.nec.co.jp> [2010-12-27 12:35:53]:

> Hi.
> 
> On Fri, 24 Dec 2010 14:39:27 +0530
> Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> 
> > * nishimura@mxp.nes.nec.co.jp <nishimura@mxp.nes.nec.co.jp> [2010-12-24 09:31:31]:
> > 
> > > Hi,
> > > 
> > > I know we have many works to be done: THP, dirty limit, per-memcg background reclaim.
> > > So, I'm not in hurry to push this patch.
> > > 
> > > This patch add checks at allocating or freeing a page whether the page is used
> > > (iow, charged) from the view point of memcg. In fact, I've hit this check while
> > > debugging a problem on RHEL6 kernel, which have stuck me these days and have not
> > > been fixed unfortunately...
> > > 
> > > ===
> > > From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> > > 
> > > This patch add checks at allocating or freeing a page whether the page is used
> > > (iow, charged) from the view point of memcg.
> > > This check may be usefull in debugging a problem and we did a similar checks
> > > before the commit 52d4b9ac(memcg: allocate all page_cgroup at boot).
> > > 
> > > This patch adds some overheads at allocating or freeing memory, so it's enabled
> > > only when CONFIG_DEBUG_VM is enabled.
> > > 
> > > Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> > > ---
> > >  include/linux/memcontrol.h |   12 +++++++++++
> > >  mm/memcontrol.c            |   47 ++++++++++++++++++++++++++++++++++++++++++++
> > >  mm/page_alloc.c            |    8 +++++-
> > >  3 files changed, 65 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > > index 067115c..04754c4 100644
> > > --- a/include/linux/memcontrol.h
> > > +++ b/include/linux/memcontrol.h
> > > @@ -146,6 +146,8 @@ 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);
> > > 
> > > +bool mem_cgroup_bad_page_check(struct page *page);
> > > +void mem_cgroup_print_bad_page(struct page *page);
> > >  #else /* CONFIG_CGROUP_MEM_RES_CTLR */
> > >  struct mem_cgroup;
> > > 
> > > @@ -336,6 +338,16 @@ u64 mem_cgroup_get_limit(struct mem_cgroup *mem)
> > >  	return 0;
> > >  }
> > > 
> > > +static inline bool
> > > +mem_cgroup_bad_page_check(struct page *page)
> > > +{
> > > +	return false;
> > > +}
> > > +
> > > +static void
> > > +mem_cgroup_print_bad_page(struct page *page)
> > > +{
> > > +}
> > >  #endif /* CONFIG_CGROUP_MEM_CONT */
> > > 
> > >  #endif /* _LINUX_MEMCONTROL_H */
> > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > > index 7d89517..21af8b2 100644
> > > --- a/mm/memcontrol.c
> > > +++ b/mm/memcontrol.c
> > > @@ -2971,6 +2971,53 @@ int mem_cgroup_shmem_charge_fallback(struct page *page,
> > >  	return ret;
> > >  }
> > > 
> > > +#ifdef CONFIG_DEBUG_VM
> > > +static bool
> > > +__mem_cgroup_bad_page_check(struct page *page, struct page_cgroup **pcp)
> > > +{
> > > +	struct page_cgroup *pc;
> > > +	bool ret = false;
> > > +
> > > +	pc = lookup_page_cgroup(page);
> > > +	if (unlikely(!pc))
> > > +		goto out;
> > > +
> > > +	if (PageCgroupUsed(pc)) {
> > > +		ret = true;
> > > +		if (pcp)
> > > +			*pcp = pc;
> > > +	}
> > > +out:
> > > +	return ret;
> > > +}
> > > +
> > > +bool mem_cgroup_bad_page_check(struct page *page)
> > > +{
> > > +	if (mem_cgroup_disabled())
> > > +		return false;
> > > +
> > > +	return __mem_cgroup_bad_page_check(page, NULL);
> > > +}
> > > +
> > > +void mem_cgroup_print_bad_page(struct page *page)
> > > +{
> > > +	struct page_cgroup *pc;
> > > +
> > > +	if (__mem_cgroup_bad_page_check(page, &pc))
> > > +		printk(KERN_ALERT "pc:%p pc->flags:%ld pc->mem_cgroup:%p\n",
> > > +			pc, pc->flags, pc->mem_cgroup);
> > 
> > I like the patch overall, I'm not sure if KERN_ALERT is the right
> > level and I'd also like to see the pfn and page information printed.
> Using the same level as dump_page() does would be better, IMHO.
> And, I think this function should show information only about memcg. Information
> about the page itself like pfn should be showed by dump_page().
>

OK, fair enough
 
> > pc->mem_cgroup itself is a pointer and not very useful, how about
> > printing pc->mem_cgroup.css->cgroup->dentry->d_name->name (Phew!)
> > 
> pc->mem_cgroup is enough to me(we can know path of it by using "crash" utility),
> but I agree showing the path of it would be more informative.
> I'll try it as mem_cgroup_print_oom_info() does.
>

Yes, because pointers are hard to follow, having a warning with more
information helps the user report better bugs on what was going on in
a particular cgroup for example.
 
-- 
	Three Cheers,
	Balbir

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>