From: Anatoly Burakov Date: Thu, 19 Nov 2020 10:52:45 +0000 (+0000) Subject: doc: update information on using hugepages X-Git-Url: http://git.droids-corp.org/?a=commitdiff_plain;h=8397cac725e43562df3ce7d230aa3b4390b64b10;p=dpdk.git doc: update information on using hugepages Current information regarding hugepage usage is a little out of date.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 Acked-by: Bruce Richardson --- diff --git a/doc/guides/linux_gsg/sys_reqs.rst b/doc/guides/linux_gsg/sys_reqs.rst index e074faf514..be714adf22 100644 --- a/doc/guides/linux_gsg/sys_reqs.rst +++ b/doc/guides/linux_gsg/sys_reqs.rst @@ -158,8 +158,36 @@ 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:: @@ -188,35 +216,29 @@ 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 +Using Hugepages with the DPDK +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -.. note:: +If secondary process support is not required, DPDK is able to use hugepages +without any configuration by using "in-memory" mode. +Please see :doc:`linux_eal_parameters` for more details. - For 1G pages, it is not possible to reserve the hugepage memory after the system has booted. +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. -Using Hugepages with the DPDK -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +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). -Once the hugepage memory is reserved, to make the memory available for DPDK use, perform the following steps:: +To make the hugepages of size 1GB available for DPDK use, +following steps must be performed:: 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