From: Anatoly Burakov <anatoly.burakov@intel.com>
To: dev@dpdk.org
Cc: John McNamara <john.mcnamara@intel.com>,
Marko Kovacevic <marko.kovacevic@intel.com>,
ferruh.yigit@intel.com, bruce.richardson@intel.com,
padraig.j.connolly@intel.com, stable@dpdk.org
Subject: [dpdk-dev] [PATCH v3 2/2] doc/linux_gsg: update information on using hugepages
Date: Tue, 25 Aug 2020 14:57:35 +0100 [thread overview]
Message-ID: <6f93d916bbceb67e09083a2be05f23a572a0d614.1598363848.git.anatoly.burakov@intel.com> (raw)
In-Reply-To: <242515b3b0d4ac57ee86cada96af90fb78e14997.1598363848.git.anatoly.burakov@intel.com>
In-Reply-To: <196e97d2802cf2250577aaa113b9093b0beadb3d.1598357863.git.anatoly.burakov@intel.com>
Current information regarding hugepage usage is a little out of date.
Update it to include information on in-memory mode, as well as on
default mountpoints provided by systemd.
Cc: stable@dpdk.org
Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>
---
Notes:
v3:
- Clarified wording around non-default hugepage sizes
v2:
- Reworked the description
- Put runtime reservation first, and boot time as an alternative
- Clarified wording and fixed typos
- Mentioned that some kernel versions not supporting reserving 1G pages
doc/guides/linux_gsg/sys_reqs.rst | 70 +++++++++++++++++++------------
1 file changed, 44 insertions(+), 26 deletions(-)
diff --git a/doc/guides/linux_gsg/sys_reqs.rst b/doc/guides/linux_gsg/sys_reqs.rst
index a124656bcb..587f9e85e5 100644
--- a/doc/guides/linux_gsg/sys_reqs.rst
+++ b/doc/guides/linux_gsg/sys_reqs.rst
@@ -155,8 +155,35 @@ Without hugepages, high TLB miss rates would occur with the standard 4k page siz
Reserving Hugepages for DPDK Use
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-The allocation of hugepages should be done at boot time or as soon as possible after system boot
-to prevent memory from being fragmented in physical memory.
+The reservation of hugepages can be performed at run time. This is done by
+echoing the number of hugepages required to a ``nr_hugepages`` file in the
+``/sys/kernel/`` directory corresponding to a specific page size (in
+Kilobytes). For a single-node system, the command to use is as follows
+(assuming that 1024 of 2MB pages are required)::
+
+ echo 1024 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
+
+On a NUMA machine, the above command will usually divide the number of hugepages
+equally across all NUMA nodes (assuming there is enough memory on all NUMA
+nodes). However, pages can also be reserved explicitly on individual NUMA
+nodes using a ``nr_hugepages`` file in the ``/sys/devices/`` directory::
+
+ echo 1024 > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages
+ echo 1024 > /sys/devices/system/node/node1/hugepages/hugepages-2048kB/nr_hugepages
+
+.. note::
+
+ Some kernel versions may not allow reserving 1 GB hugepages at run time, so
+ reserving them at boot time may be the only option. Please see below for
+ instructions.
+
+**Alternative:**
+
+In the general case, reserving hugepages at run time is perfectly fine, but in
+use cases where having lots of physically contiguous memory is required, it is
+preferable to reserve hugepages at boot time, as that will help in preventing
+physical memory from becoming heavily fragmented.
+
To reserve hugepages at boot time, a parameter is passed to the Linux kernel on the kernel command line.
For 2 MB pages, just pass the hugepages option to the kernel. For example, to reserve 1024 pages of 2 MB, use::
@@ -185,35 +212,26 @@ the number of hugepages reserved at boot time is generally divided equally betwe
See the Documentation/admin-guide/kernel-parameters.txt file in your Linux source tree for further details of these and other kernel options.
-**Alternative:**
-
-For 2 MB pages, there is also the option of allocating hugepages after the system has booted.
-This is done by echoing the number of hugepages required to a nr_hugepages file in the ``/sys/devices/`` directory.
-For a single-node system, the command to use is as follows (assuming that 1024 pages are required)::
-
- echo 1024 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
-
-On a NUMA machine, pages should be allocated explicitly on separate nodes::
-
- echo 1024 > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages
- echo 1024 > /sys/devices/system/node/node1/hugepages/hugepages-2048kB/nr_hugepages
-
-.. note::
-
- For 1G pages, it is not possible to reserve the hugepage memory after the system has booted.
-
Using Hugepages with the DPDK
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-Once the hugepage memory is reserved, to make the memory available for DPDK use, perform the following steps::
+If secondary process support is not required, DPDK is able to use hugepages
+without any configuration by using "in-memory" mode. Please see
+:ref:`linux_eal_parameters` for more details.
+
+If secondary process support is required, mount points for hugepages need to be
+created. On modern Linux distributions, a default mount point for hugepages is provided
+by the system and is located at ``/dev/hugepages``. This mount point will use the
+default hugepage size set by the kernel parameters as described above.
+
+However, in order to use hugepage sizes other than the default, it is necessary
+to manually create mount points for those hugepage sizes (e.g. 1GB pages).
+
+To make the hugepages of size 1GB available for DPDK use, perform the following steps::
mkdir /mnt/huge
- mount -t hugetlbfs nodev /mnt/huge
+ mount -t hugetlbfs pagesize=1GB /mnt/huge
The mount point can be made permanent across reboots, by adding the following line to the ``/etc/fstab`` file::
- nodev /mnt/huge hugetlbfs defaults 0 0
-
-For 1GB pages, the page size must be specified as a mount option::
-
- nodev /mnt/huge_1GB hugetlbfs pagesize=1GB 0 0
+ nodev /mnt/huge hugetlbfs pagesize=1GB 0 0
--
2.17.1
next prev parent reply other threads:[~2020-08-25 13:57 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-24 15:45 [dpdk-dev] [PATCH 1/2] doc/linux_gsg: clarify instructions on running as non-root Anatoly Burakov
2020-08-24 15:45 ` [dpdk-dev] [PATCH 2/2] doc/linux_gsg: update information on using hugepages Anatoly Burakov
2020-08-24 17:13 ` Bruce Richardson
2020-08-25 9:28 ` Burakov, Anatoly
2020-08-24 17:08 ` [dpdk-dev] [PATCH 1/2] doc/linux_gsg: clarify instructions on running as non-root Bruce Richardson
2020-08-25 9:29 ` Burakov, Anatoly
2020-08-25 7:47 ` Ferruh Yigit
2020-08-25 12:17 ` [dpdk-dev] [PATCH v2 " Anatoly Burakov
2020-08-25 13:06 ` Bruce Richardson
2020-08-25 13:57 ` [dpdk-dev] [PATCH v3 " Anatoly Burakov
2020-11-19 10:52 ` [dpdk-dev] [PATCH v4 1/2] doc: " Anatoly Burakov
2020-11-19 10:52 ` [dpdk-dev] [PATCH v4 2/2] doc/linux_gsg: update information on using hugepages Anatoly Burakov
2020-11-19 21:03 ` David Marchand
2020-11-20 10:50 ` Burakov, Anatoly
2020-11-27 15:23 ` [dpdk-dev] [dpdk-stable] " Thomas Monjalon
2020-08-25 13:57 ` Anatoly Burakov [this message]
2020-08-25 12:17 ` [dpdk-dev] [PATCH v2 " Anatoly Burakov
2020-08-25 13:10 ` Bruce Richardson
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