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SubjectRe: [PATCH 0/6] mm/hugetlb: gigantic hugetlb page pools shrink supporting
On Fri 05-04-13 07:41:23, Wanpeng Li wrote:
> On Thu, Apr 04, 2013 at 06:17:46PM +0200, Michal Hocko wrote:
> >On Thu 04-04-13 17:09:08, Wanpeng Li wrote:
> >> order >= MAX_ORDER pages are only allocated at boot stage using the
> >> bootmem allocator with the "hugepages=xxx" option. These pages are never
> >> free after boot by default since it would be a one-way street(>= MAX_ORDER
> >> pages cannot be allocated later), but if administrator confirm not to
> >> use these gigantic pages any more, these pinned pages will waste memory
> >> since other users can't grab free pages from gigantic hugetlb pool even
> >> if OOM, it's not flexible. The patchset add hugetlb gigantic page pools
> >> shrink supporting. Administrator can enable knob exported in sysctl to
> >> permit to shrink gigantic hugetlb pool.
> >
> >I am not sure I see why the new knob is needed.
> >/sys/kernel/mm/hugepages/hugepages-*/nr_hugepages is root interface so
> >an additional step to allow writing to the file doesn't make much sense
> >to me to be honest.
> >
> >Support for shrinking gigantic huge pages makes some sense to me but I
> >would be interested in the real world example. GB pages are usually used
> >in very specific environments where the amount is usually well known.
>
> Gigantic huge pages in hugetlb means h->order >= MAX_ORDER instead of GB
> pages. ;-)

Yes, I am aware of that but the question remains the same (and
unanswered). What is the use case?

--
Michal Hocko
SUSE Labs


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