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From: Mina Almasry <almasrymina@google.com>
To: mike.kravetz@oracle.com
Cc: shuah@kernel.org, almasrymina@google.com, rientjes@google.com,
	shakeelb@google.com, gthelen@google.com,
	akpm@linux-foundation.org, khalid.aziz@oracle.com,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-kselftest@vger.kernel.org, cgroups@vger.kernel.org,
	aneesh.kumar@linux.vnet.ibm.com, mkoutny@suse.com,
	Hillf Danton <hdanton@sina.com>
Subject: [PATCH v6 9/9] hugetlb_cgroup: Add hugetlb_cgroup reservation docs
Date: Sat, 12 Oct 2019 17:30:24 -0700
Message-ID: <20191013003024.215429-9-almasrymina@google.com> (raw)
In-Reply-To: <20191013003024.215429-1-almasrymina@google.com>

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

      parent reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-13  0:30 [PATCH v6 1/9] hugetlb_cgroup: Add hugetlb_cgroup reservation counter Mina Almasry
2019-10-13  0:30 ` [PATCH v6 2/9] hugetlb_cgroup: add interface for charge/uncharge hugetlb reservations Mina Almasry
2019-10-13  0:30 ` [PATCH v6 3/9] hugetlb_cgroup: add cgroup-v2 support Mina Almasry
2019-10-13  0:30 ` [PATCH v6 4/9] hugetlb_cgroup: add reservation accounting for private mappings Mina Almasry
2019-10-13  0:30 ` [PATCH v6 5/9] hugetlb: disable region_add file_region coalescing Mina Almasry
2019-10-13  0:30 ` [PATCH v6 6/9] hugetlb_cgroup: add accounting for shared mappings Mina Almasry
2019-10-13  0:30 ` [PATCH v6 7/9] hugetlb_cgroup: support noreserve mappings Mina Almasry
2019-10-13  0:30 ` [PATCH v6 8/9] hugetlb_cgroup: Add hugetlb_cgroup reservation tests Mina Almasry
2019-10-13  0:30 ` Mina Almasry [this message]

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