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.
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
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