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@xxxxxxxxxxxxxxxxxx> 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.
>
> > --- 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:
>
> > + 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'.
Thanks,
Davidlohr
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