136 lines
6.0 KiB
ReStructuredText
136 lines
6.0 KiB
ReStructuredText
|
==================
|
||
|
|
HugeTLB Controller
|
||
|
|
==================
|
||
|
|
|
||
|
|
HugeTLB controller can be created by first mounting the cgroup filesystem.
|
||
|
|
|
||
|
|
# mount -t cgroup -o hugetlb none /sys/fs/cgroup
|
||
|
|
|
||
|
|
With the above step, the initial or the parent HugeTLB group becomes
|
||
|
|
visible at /sys/fs/cgroup. At bootup, this group includes all the tasks in
|
||
|
|
the system. /sys/fs/cgroup/tasks lists the tasks in this cgroup.
|
||
|
|
|
||
|
|
New groups can be created under the parent group /sys/fs/cgroup::
|
||
|
|
|
||
|
|
# cd /sys/fs/cgroup
|
||
|
|
# mkdir g1
|
||
|
|
# echo $$ > g1/tasks
|
||
|
|
|
||
|
|
The above steps create a new group g1 and move the current shell
|
||
|
|
process (bash) into it.
|
||
|
|
|
||
|
|
Brief summary of control files::
|
||
|
|
|
||
|
|
hugetlb.<hugepagesize>.rsvd.limit_in_bytes # set/show limit of "hugepagesize" hugetlb reservations
|
||
|
|
hugetlb.<hugepagesize>.rsvd.max_usage_in_bytes # show max "hugepagesize" hugetlb reservations and no-reserve faults
|
||
|
|
hugetlb.<hugepagesize>.rsvd.usage_in_bytes # show current reservations and no-reserve faults for "hugepagesize" hugetlb
|
||
|
|
hugetlb.<hugepagesize>.rsvd.failcnt # show the number of allocation failure due to HugeTLB reservation limit
|
||
|
|
hugetlb.<hugepagesize>.limit_in_bytes # set/show limit of "hugepagesize" hugetlb faults
|
||
|
|
hugetlb.<hugepagesize>.max_usage_in_bytes # show max "hugepagesize" hugetlb usage recorded
|
||
|
|
hugetlb.<hugepagesize>.usage_in_bytes # show current usage for "hugepagesize" hugetlb
|
||
|
|
hugetlb.<hugepagesize>.failcnt # show the number of allocation failure due to HugeTLB usage limit
|
||
|
|
hugetlb.<hugepagesize>.numa_stat # show the numa information of the hugetlb memory charged to this cgroup
|
||
|
|
|
||
|
|
For a system supporting three hugepage sizes (64k, 32M and 1G), the control
|
||
|
|
files include::
|
||
|
|
|
||
|
|
hugetlb.1GB.limit_in_bytes
|
||
|
|
hugetlb.1GB.max_usage_in_bytes
|
||
|
|
hugetlb.1GB.numa_stat
|
||
|
|
hugetlb.1GB.usage_in_bytes
|
||
|
|
hugetlb.1GB.failcnt
|
||
|
|
hugetlb.1GB.rsvd.limit_in_bytes
|
||
|
|
hugetlb.1GB.rsvd.max_usage_in_bytes
|
||
|
|
hugetlb.1GB.rsvd.usage_in_bytes
|
||
|
|
hugetlb.1GB.rsvd.failcnt
|
||
|
|
hugetlb.64KB.limit_in_bytes
|
||
|
|
hugetlb.64KB.max_usage_in_bytes
|
||
|
|
hugetlb.64KB.numa_stat
|
||
|
|
hugetlb.64KB.usage_in_bytes
|
||
|
|
hugetlb.64KB.failcnt
|
||
|
|
hugetlb.64KB.rsvd.limit_in_bytes
|
||
|
|
hugetlb.64KB.rsvd.max_usage_in_bytes
|
||
|
|
hugetlb.64KB.rsvd.usage_in_bytes
|
||
|
|
hugetlb.64KB.rsvd.failcnt
|
||
|
|
hugetlb.32MB.limit_in_bytes
|
||
|
|
hugetlb.32MB.max_usage_in_bytes
|
||
|
|
hugetlb.32MB.numa_stat
|
||
|
|
hugetlb.32MB.usage_in_bytes
|
||
|
|
hugetlb.32MB.failcnt
|
||
|
|
hugetlb.32MB.rsvd.limit_in_bytes
|
||
|
|
hugetlb.32MB.rsvd.max_usage_in_bytes
|
||
|
|
hugetlb.32MB.rsvd.usage_in_bytes
|
||
|
|
hugetlb.32MB.rsvd.failcnt
|
||
|
|
|
||
|
|
|
||
|
|
1. Page fault accounting
|
||
|
|
|
||
|
|
hugetlb.<hugepagesize>.limit_in_bytes
|
||
|
|
hugetlb.<hugepagesize>.max_usage_in_bytes
|
||
|
|
hugetlb.<hugepagesize>.usage_in_bytes
|
||
|
|
hugetlb.<hugepagesize>.failcnt
|
||
|
|
|
||
|
|
The HugeTLB controller allows users to limit the HugeTLB usage (page fault) per
|
||
|
|
control group and enforces the limit during page fault. Since HugeTLB
|
||
|
|
doesn't support page reclaim, enforcing the limit at page fault time implies
|
||
|
|
that, the application will get SIGBUS signal if it tries to fault in HugeTLB
|
||
|
|
pages beyond its limit. Therefore the application needs to know exactly how many
|
||
|
|
HugeTLB pages it uses before hand, and the sysadmin needs to make sure that
|
||
|
|
there are enough available on the machine for all the users to avoid processes
|
||
|
|
getting SIGBUS.
|
||
|
|
|
||
|
|
|
||
|
|
2. Reservation accounting
|
||
|
|
|
||
|
|
hugetlb.<hugepagesize>.rsvd.limit_in_bytes
|
||
|
|
hugetlb.<hugepagesize>.rsvd.max_usage_in_bytes
|
||
|
|
hugetlb.<hugepagesize>.rsvd.usage_in_bytes
|
||
|
|
hugetlb.<hugepagesize>.rsvd.failcnt
|
||
|
|
|
||
|
|
The HugeTLB controller allows to limit the HugeTLB reservations per control
|
||
|
|
group and enforces the controller limit at reservation time and at the fault of
|
||
|
|
HugeTLB memory for which no reservation exists. Since reservation limits are
|
||
|
|
enforced at reservation time (on mmap or shget), reservation limits never causes
|
||
|
|
the application to get SIGBUS signal if the memory was reserved before hand. For
|
||
|
|
MAP_NORESERVE allocations, the reservation limit behaves the same as the fault
|
||
|
|
limit, enforcing memory usage at fault time and causing the application to
|
||
|
|
receive a SIGBUS if it's crossing its limit.
|
||
|
|
|
||
|
|
Reservation limits are superior to page fault limits described above, since
|
||
|
|
reservation limits are enforced at reservation time (on mmap or shget), and
|
||
|
|
never causes the application to get SIGBUS signal if the memory was reserved
|
||
|
|
before hand. This allows for easier fallback to alternatives such as
|
||
|
|
non-HugeTLB memory for example. In the case of page fault accounting, it's very
|
||
|
|
hard to avoid processes getting SIGBUS since the sysadmin needs precisely know
|
||
|
|
the HugeTLB usage of all the tasks in the system and make sure there is enough
|
||
|
|
pages to satisfy all requests. Avoiding tasks getting SIGBUS on overcommited
|
||
|
|
systems is practically impossible with page fault accounting.
|
||
|
|
|
||
|
|
|
||
|
|
3. Caveats with shared memory
|
||
|
|
|
||
|
|
For shared HugeTLB memory, both HugeTLB reservation and page faults are charged
|
||
|
|
to the first task that causes the memory to be reserved or faulted, and all
|
||
|
|
subsequent uses of this reserved or faulted memory is done without charging.
|
||
|
|
|
||
|
|
Shared HugeTLB memory is only uncharged when it is unreserved or deallocated.
|
||
|
|
This is usually when the HugeTLB file is deleted, and not when the task that
|
||
|
|
caused the reservation or fault has exited.
|
||
|
|
|
||
|
|
|
||
|
|
4. Caveats with HugeTLB cgroup offline.
|
||
|
|
|
||
|
|
When a HugeTLB cgroup goes offline with some reservations or faults still
|
||
|
|
charged to it, the behavior is as follows:
|
||
|
|
|
||
|
|
- The fault charges are charged to the parent HugeTLB cgroup (reparented),
|
||
|
|
- the reservation charges remain on the offline HugeTLB cgroup.
|
||
|
|
|
||
|
|
This means that if a HugeTLB cgroup gets offlined while there is still HugeTLB
|
||
|
|
reservations charged to it, that cgroup persists as a zombie until all HugeTLB
|
||
|
|
reservations are uncharged. HugeTLB reservations behave in this manner to match
|
||
|
|
the memory controller whose cgroups also persist as zombie until all charged
|
||
|
|
memory is uncharged. Also, the tracking of HugeTLB reservations is a bit more
|
||
|
|
complex compared to the tracking of HugeTLB faults, so it is significantly
|
||
|
|
harder to reparent reservations at offline time.
|