On Fri 05-04-13 16:54:44, Simon Jeons wrote: > Hi Michal, > On 04/05/2013 04:12 PM, Michal Hocko wrote: > >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? > > As patch description, "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". Is this a use case that we care about? How often something like that happens? I understand this is "nice to have" but I am interested whether somebody actually _needs_ this. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>