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

[Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>]

Hi.

On Fri, 24 Dec 2010 09:37:39 +0100
Johannes Weiner <hannes@cmpxchg.org> wrote:

> On Fri, Dec 24, 2010 at 09:31:31AM +0900, Daisuke Nishimura wrote:
> > 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>
> 

> > --- 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);
> 
> Can you put those under CONFIG_DEBUG_VM and the dummies below under
> !CONFIG_CGROUP_MEM_RES_CTLR || !CONFIG_DEBUG_VM?
> 
> The most likely configuration on distro kernels is memcg enabled and
> VM debugging disabled.  It would be good to save the unneeded function
> calls in the allocator hotpath for the common case.
> 
Will do.

> Also:
> 
> > @@ -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
> 
> That needs an `inline' as well.
> 
Will do.

> > --- 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;
> 
> I think it is not necessary to have two return values.  Just return
> the pc if it's in use:
> 
> static struct page_cgroup *lookup_page_cgroup_used(struct page)
> {
> 	struct page_cgroup *pc;
> 
> 	pc = lookup_page_cgroup(page);
> 	if (likely(pc) && PageCgroupUsed(pc))
> 		return pc;
> 	return NULL;
> }
> 
Nice idea.

> > +bool mem_cgroup_bad_page_check(struct page *page)
> > +{
> > +	if (mem_cgroup_disabled())
> > +		return false;
> > +
> > +	return __mem_cgroup_bad_page_check(page, NULL);
> 
> 	return !!lookup_page_cgroup_used(page);
> 
> > +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);
> 
> 	pc = lookup_page_cgroup_used(page);
> 	if (pc)
> 		printk()
> 
> Other than that, I agree with the patch.

Thank you for your reviews!


Daisuke Nishimura.

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