Linux-kselftest Archive on lore.kernel.org
 help / color / Atom feed
From: Mina Almasry <almasrymina@google.com>
To: mike.kravetz@oracle.com, rientjes@google.com, shakeelb@google.com
Cc: shuah@kernel.org, almasrymina@google.com, gthelen@google.com,
	akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
	cgroups@vger.kernel.org, aneesh.kumar@linux.vnet.ibm.com
Subject: [PATCH v10 8/8] hugetlb_cgroup: Add hugetlb_cgroup reservation docs
Date: Tue, 14 Jan 2020 17:26:51 -0800
Message-ID: <20200115012651.228058-8-almasrymina@google.com> (raw)
In-Reply-To: <20200115012651.228058-1-almasrymina@google.com>

Add docs for how to use hugetlb_cgroup reservations, and their behavior.

Signed-off-by: Mina Almasry <almasrymina@google.com>

---

Changes in v10:
- Clarify reparenting behavior.
- Reword benefits of reservation limits.
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         | 103 ++++++++++++++++--
 1 file changed, 92 insertions(+), 11 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v1/hugetlb.rst b/Documentation/admin-guide/cgroup-v1/hugetlb.rst
index a3902aa253a96..00dd4daf55f19 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>.resv.limit_in_bytes            # set/show limit of "hugepagesize" hugetlb reservations
+ hugetlb.<hugepagesize>.resv.max_usage_in_bytes        # show max "hugepagesize" hugetlb reservations and no-reserve faults
+ hugetlb.<hugepagesize>.resv.usage_in_bytes            # show current reservations and no-reserve faults for "hugepagesize" hugetlb
+ hugetlb.<hugepagesize>.resv.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 +37,95 @@ files include::
   hugetlb.1GB.max_usage_in_bytes
   hugetlb.1GB.usage_in_bytes
   hugetlb.1GB.failcnt
+  hugetlb.1GB.resv.limit_in_bytes
+  hugetlb.1GB.resv.max_usage_in_bytes
+  hugetlb.1GB.resv.usage_in_bytes
+  hugetlb.1GB.resv.failcnt
   hugetlb.64KB.limit_in_bytes
   hugetlb.64KB.max_usage_in_bytes
   hugetlb.64KB.usage_in_bytes
   hugetlb.64KB.failcnt
+  hugetlb.64KB.resv.limit_in_bytes
+  hugetlb.64KB.resv.max_usage_in_bytes
+  hugetlb.64KB.resv.usage_in_bytes
+  hugetlb.64KB.resv.failcnt
   hugetlb.32MB.limit_in_bytes
   hugetlb.32MB.max_usage_in_bytes
   hugetlb.32MB.usage_in_bytes
   hugetlb.32MB.failcnt
+  hugetlb.32MB.resv.limit_in_bytes
+  hugetlb.32MB.resv.max_usage_in_bytes
+  hugetlb.32MB.resv.usage_in_bytes
+  hugetlb.32MB.resv.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>.resv.limit_in_bytes
+hugetlb.<hugepagesize>.resv.max_usage_in_bytes
+hugetlb.<hugepagesize>.resv.usage_in_bytes
+hugetlb.<hugepagesize>.resv.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.
--
2.25.0.rc1.283.g88dfdc4193-goog

  parent reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-15  1:26 [PATCH v10 1/8] hugetlb_cgroup: Add hugetlb_cgroup reservation counter Mina Almasry
2020-01-15  1:26 ` [PATCH v10 2/8] hugetlb_cgroup: add interface for charge/uncharge hugetlb reservations Mina Almasry
2020-01-17 19:26   ` Mike Kravetz
2020-01-17 19:34     ` Mina Almasry
2020-01-29 21:21   ` David Rientjes
2020-01-30  0:41     ` Mike Kravetz
2020-01-15  1:26 ` [PATCH v10 3/8] hugetlb_cgroup: add reservation accounting for private mappings Mina Almasry
2020-01-17 22:57   ` Mike Kravetz
2020-01-29 21:28   ` David Rientjes
2020-02-03 23:17     ` Mina Almasry
2020-01-15  1:26 ` [PATCH v10 4/8] hugetlb: disable region_add file_region coalescing Mina Almasry
2020-01-21 18:50   ` Mike Kravetz
2020-01-15  1:26 ` [PATCH v10 5/8] hugetlb_cgroup: add accounting for shared mappings Mina Almasry
2020-01-15  1:26 ` [PATCH v10 6/8] hugetlb_cgroup: support noreserve mappings Mina Almasry
2020-01-15  1:26 ` [PATCH v10 7/8] hugetlb_cgroup: Add hugetlb_cgroup reservation tests Mina Almasry
2020-01-23  9:15   ` Sandipan Das
2020-01-23 20:05     ` Mina Almasry
2020-01-29 21:00     ` David Rientjes
2020-01-30  6:11       ` Sandipan Das
2020-02-03 23:18         ` Mina Almasry
2020-01-15  1:26 ` Mina Almasry [this message]
2020-01-16 22:44 ` [PATCH v10 1/8] hugetlb_cgroup: Add hugetlb_cgroup reservation counter Mike Kravetz
2020-01-29 21:09 ` David Rientjes
2020-02-03 23:16   ` Mina Almasry

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200115012651.228058-8-almasrymina@google.com \
    --to=almasrymina@google.com \
    --cc=akpm@linux-foundation.org \
    --cc=aneesh.kumar@linux.vnet.ibm.com \
    --cc=cgroups@vger.kernel.org \
    --cc=gthelen@google.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-kselftest@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mike.kravetz@oracle.com \
    --cc=rientjes@google.com \
    --cc=shakeelb@google.com \
    --cc=shuah@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-kselftest Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-kselftest/0 linux-kselftest/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-kselftest linux-kselftest/ https://lore.kernel.org/linux-kselftest \
		linux-kselftest@vger.kernel.org
	public-inbox-index linux-kselftest

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kselftest


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git