[v4,2/2] doc/linux_gsg: update information on using hugepages
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Message ID 232d6d0413903434d0dcef516570d424d0dfab53.1605783141.git.anatoly.burakov@intel.com
State New
Delegated to: Thomas Monjalon
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  • [v4,1/2] doc: clarify instructions on running as non-root
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Commit Message

Anatoly Burakov Nov. 19, 2020, 10:52 a.m. UTC
Current information regarding hugepage usage is a little out of date.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(-)

Comments

David Marchand Nov. 19, 2020, 9:03 p.m. UTC | #1
On Thu, Nov 19, 2020 at 11:53 AM Anatoly Burakov
<anatoly.burakov@intel.com> wrote:
> -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.

There is no such reference:

Found ninja-1.9.0 at /usr/bin/ninja
[3/4] Generating html_guides with a custom command.
Install the sphinx ReadTheDocs theme for improved html documentation
layout: https://sphinx-rtd-theme.readthedocs.io/
/home/dmarchan/dpdk/doc/guides/linux_gsg/sys_reqs.rst:210: WARNING:
undefined label: linux_eal_parameters (if the link has no caption the
label must precede a section header)
[3/4] Running external command doc.
Building docs: Doxygen_API HTML_Guides

Did you mean :doc: ?
Anatoly Burakov Nov. 20, 2020, 10:50 a.m. UTC | #2
On 19-Nov-20 9:03 PM, David Marchand wrote:
> On Thu, Nov 19, 2020 at 11:53 AM Anatoly Burakov
> <anatoly.burakov@intel.com> wrote:
>> -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.
> 
> There is no such reference:
> 
> Found ninja-1.9.0 at /usr/bin/ninja
> [3/4] Generating html_guides with a custom command.
> Install the sphinx ReadTheDocs theme for improved html documentation
> layout: https://sphinx-rtd-theme.readthedocs.io/
> /home/dmarchan/dpdk/doc/guides/linux_gsg/sys_reqs.rst:210: WARNING:
> undefined label: linux_eal_parameters (if the link has no caption the
> label must precede a section header)
> [3/4] Running external command doc.
> Building docs: Doxygen_API HTML_Guides
> 
> Did you mean :doc: ?
> 
> 

Most probably yes, i have. Fix or respin?

Patch
diff mbox series

diff --git a/doc/guides/linux_gsg/sys_reqs.rst b/doc/guides/linux_gsg/sys_reqs.rst
index 6ecdc04aa9..3966c30456 100644
--- a/doc/guides/linux_gsg/sys_reqs.rst
+++ b/doc/guides/linux_gsg/sys_reqs.rst
@@ -147,8 +147,35 @@  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::
@@ -177,35 +204,26 @@  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