On Fri, Apr 05, 2013 at 10:12:39AM +0200, 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? The use case I can figure out is when memory pressure is serious and gigantic huge pages pools still pin large number of free pages. Regards, Wanpeng Li > >-- >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>