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Subject[PATCH v6 9/9] hugetlb_cgroup: Add hugetlb_cgroup reservation docs
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Add docs for how to use hugetlb_cgroup reservations, and their behavior.

Signed-off-by: Mina Almasry <almasrymina@google.com>
Acked-by: Hillf Danton <hdanton@sina.com>

---

Changes in v6:
- Updated docs to reflect the new design based on a new counter that
tracks both reservations and faults.

---
.../admin-guide/cgroup-v1/hugetlb.rst | 64 +++++++++++++++----
1 file changed, 53 insertions(+), 11 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v1/hugetlb.rst b/Documentation/admin-guide/cgroup-v1/hugetlb.rst
index a3902aa253a96..efb94e4db9d5a 100644
--- a/Documentation/admin-guide/cgroup-v1/hugetlb.rst
+++ b/Documentation/admin-guide/cgroup-v1/hugetlb.rst
@@ -2,13 +2,6 @@
HugeTLB Controller
==================

-The HugeTLB controller allows to limit the HugeTLB usage per control group and
-enforces the controller 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 access HugeTLB pages
-beyond its limit. This requires the application to know beforehand how much
-HugeTLB pages it would require for its use.
-
HugeTLB controller can be created by first mounting the cgroup filesystem.

# mount -t cgroup -o hugetlb none /sys/fs/cgroup
@@ -28,10 +21,14 @@ process (bash) into it.

Brief summary of control files::

- hugetlb.<hugepagesize>.limit_in_bytes # set/show limit of "hugepagesize" hugetlb usage
- 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 limit
+ hugetlb.<hugepagesize>.reservation_limit_in_bytes # set/show limit of "hugepagesize" hugetlb reservations
+ hugetlb.<hugepagesize>.reservation_max_usage_in_bytes # show max "hugepagesize" hugetlb reservations and no-reserve faults.
+ hugetlb.<hugepagesize>.reservation_usage_in_bytes # show current reservations and no-reserve faults for "hugepagesize" hugetlb
+ hugetlb.<hugepagesize>.reservation_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

For a system supporting three hugepage sizes (64k, 32M and 1G), the control
files include::
@@ -40,11 +37,56 @@ files include::
hugetlb.1GB.max_usage_in_bytes
hugetlb.1GB.usage_in_bytes
hugetlb.1GB.failcnt
+ hugetlb.1GB.reservation_limit_in_bytes
+ hugetlb.1GB.reservation_max_usage_in_bytes
+ hugetlb.1GB.reservation_usage_in_bytes
+ hugetlb.1GB.reservation_failcnt
hugetlb.64KB.limit_in_bytes
hugetlb.64KB.max_usage_in_bytes
hugetlb.64KB.usage_in_bytes
hugetlb.64KB.failcnt
+ hugetlb.64KB.reservation_limit_in_bytes
+ hugetlb.64KB.reservation_max_usage_in_bytes
+ hugetlb.64KB.reservation_usage_in_bytes
+ hugetlb.64KB.reservation_failcnt
hugetlb.32MB.limit_in_bytes
hugetlb.32MB.max_usage_in_bytes
hugetlb.32MB.usage_in_bytes
hugetlb.32MB.failcnt
+ hugetlb.32MB.reservation_limit_in_bytes
+ hugetlb.32MB.reservation_max_usage_in_bytes
+ hugetlb.32MB.reservation_usage_in_bytes
+ hugetlb.32MB.reservation_failcnt
+
+
+1. Reservation limits
+
+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. Reservation limits
+are superior to Page fault limits (see section 2), 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. 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.
+
+2. Page fault limits
+
+The HugeTLB controller allows to limit the HugeTLB usage (page fault) per
+control group and enforces the controller 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 access HugeTLB
+pages beyond its limit. This requires the application to know beforehand how
+much HugeTLB pages it would require for its use.
+
+
+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 hugetlbfs file is deleted, and not when the task that
+caused the reservation or fault has exited.
--
2.23.0.700.g56cf767bdb-goog
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