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. ;-) Regards, Wanpeng Li > >I could imagine nr_hugepages_mempolicy would make more sense to free >pages from particular nodes so they could be offlined for example. >Does the patchset handles this as well? > >> Testcase: >> boot: hugepagesz=1G hugepages=10 >> >> [root@localhost hugepages]# free -m >> total used free shared buffers cached >> Mem: 36269 10836 25432 0 11 288 >> -/+ buffers/cache: 10537 25732 >> Swap: 35999 0 35999 >> [root@localhost hugepages]# echo 0 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages >> -bash: echo: write error: Invalid argument >> [root@localhost hugepages]# echo 1 > /proc/sys/vm/hugetlb_shrink_gigantic_pool >> [root@localhost hugepages]# echo 0 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages >> [root@localhost hugepages]# free -m >> total used free shared buffers cached >> Mem: 36269 597 35672 0 11 288 >> -/+ buffers/cache: 297 35972 >> Swap: 35999 0 35999 >> >> Wanpeng Li (6): >> introduce new sysctl knob which control gigantic page pools shrinking >> update_and_free_page gigantic pages awareness >> enable gigantic hugetlb page pools shrinking >> use already exist huge_page_order() instead of h->order >> remove redundant hugetlb_prefault >> use already exist interface huge_page_shift >> >> Documentation/sysctl/vm.txt | 13 +++++++ >> include/linux/hugetlb.h | 5 +-- >> kernel/sysctl.c | 7 ++++ >> mm/hugetlb.c | 83 +++++++++++++++++++++++++++++-------------- >> mm/internal.h | 1 + >> mm/page_alloc.c | 2 +- >> 6 files changed, 82 insertions(+), 29 deletions(-) >> >> -- >> 1.7.10.4 >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in >> the body of a message to majordomo@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> Please read the FAQ at http://www.tux.org/lkml/ > >-- >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>