linux-kernel - Re: [PATCH V3] mm/thp: Allocate transparent hugepages on local node

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Date:	Sun, 18 Jan 2015 21:20:58 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Davidlohr Bueso <dave@...olabs.net>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	David Rientjes <rientjes@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3] mm/thp: Allocate transparent hugepages on local node

Davidlohr Bueso <dave@...olabs.net> writes:

> On Fri, 2015-01-16 at 16:02 -0800, Andrew Morton wrote:
>> On Fri, 16 Jan 2015 12:56:36 +0530 "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> wrote:
>> 
>> > This make sure that we try to allocate hugepages from local node if
>> > allowed by mempolicy. If we can't, we fallback to small page allocation
>> > based on mempolicy. This is based on the observation that allocating pages
>> > on local node is more beneficial than allocating hugepages on remote node.
>> 
>> The changelog is a bit incomplete.  It doesn't describe the current
>> behaviour, nor what is wrong with it.  What are the before-and-after
>> effects of this change?
>> 
>> And what might be the user-visible effects?
>
> I'd be interested in any performance data. I'll run this by a 4 node box
> next week.


Thanks.

>
>> 
>> > --- a/mm/mempolicy.c
>> > +++ b/mm/mempolicy.c
>> > @@ -2030,6 +2030,46 @@ retry_cpuset:
>> >  	return page;
>> >  }
>> >  
>> > +struct page *alloc_hugepage_vma(gfp_t gfp, struct vm_area_struct *vma,
>> > +				unsigned long addr, int order)
>> 
>> alloc_pages_vma() is nicely documented.  alloc_hugepage_vma() is not
>> documented at all.  This makes it a bit had for readers to work out the
>> difference!
>> 
>> Is it possible to scrunch them both into the same function?  Probably
>> too messy?
>> 
>> > +{
>> > +	struct page *page;
>> > +	nodemask_t *nmask;
>> > +	struct mempolicy *pol;
>> > +	int node = numa_node_id();
>> > +	unsigned int cpuset_mems_cookie;
>> > +
>> > +retry_cpuset:
>> > +	pol = get_vma_policy(vma, addr);
>> > +	cpuset_mems_cookie = read_mems_allowed_begin();
>> > +
>> > +	if (pol->mode != MPOL_INTERLEAVE) {
>> > +		/*
>> > +		 * For interleave policy, we don't worry about
>> > +		 * current node. Otherwise if current node is
>> > +		 * in nodemask, try to allocate hugepage from
>> > +		 * current node. Don't fall back to other nodes
>> > +		 * for THP.
>> > +		 */
>> 
>> This code isn't "interleave policy".  It's everything *but* interleave
>> policy.  Comment makes no sense!
>
> May I add that, while a nit, this indentation is quite ugly:

I updated that and replied here
http://article.gmane.org/gmane.linux.kernel/1868545. Let me know what you think.
>
>> 
>> > +		nmask = policy_nodemask(gfp, pol);
>> > +		if (!nmask || node_isset(node, *nmask)) {
>> > +			mpol_cond_put(pol);
>> > +			page = alloc_pages_exact_node(node, gfp, order);
>> > +			if (unlikely(!page &&
>> > +				     read_mems_allowed_retry(cpuset_mems_cookie)))
>> > +				goto retry_cpuset;
>> > +			return page;
>> > +		}
>> > +	}
>
> Improving it makes the code visually easier on the eye. So this should
> be considered if another re-spin of the patch is to be done anyway. Just
> jump to the mpol refcounting and be done when 'pol->mode ==
> MPOL_INTERLEAVE'.
>


-aneesh

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