[PATCH v6 5/6] mm/mempolicy: Advertise new MPOL_PREFERRED_MANY
From: Feng Tang <hidden>
Date: 2021-07-12 09:04:18
Also in:
linux-api, lkml
Subsystem:
documentation, memory management, memory management - memory policy and migration, memory management - misc, the rest · Maintainers:
Jonathan Corbet, Andrew Morton, David Hildenbrand, Linus Torvalds
From: Ben Widawsky <redacted> Adds a new mode to the existing mempolicy modes, MPOL_PREFERRED_MANY. MPOL_PREFERRED_MANY will be adequately documented in the internal admin-guide with this patch. Eventually, the man pages for mbind(2), get_mempolicy(2), set_mempolicy(2) and numactl(8) will also have text about this mode. Those shall contain the canonical reference. NUMA systems continue to become more prevalent. New technologies like PMEM make finer grain control over memory access patterns increasingly desirable. MPOL_PREFERRED_MANY allows userspace to specify a set of nodes that will be tried first when performing allocations. If those allocations fail, all remaining nodes will be tried. It's a straight forward API which solves many of the presumptive needs of system administrators wanting to optimize workloads on such machines. The mode will work either per VMA, or per thread. Link: https://lore.kernel.org/r/20200630212517.308045-13-ben.widawsky@intel.com (local) Signed-off-by: Ben Widawsky <redacted> Signed-off-by: Feng Tang <redacted> --- Documentation/admin-guide/mm/numa_memory_policy.rst | 16 ++++++++++++---- mm/mempolicy.c | 7 +------ 2 files changed, 13 insertions(+), 10 deletions(-)
diff --git a/Documentation/admin-guide/mm/numa_memory_policy.rst b/Documentation/admin-guide/mm/numa_memory_policy.rst
index 067a90a1499c..cd653561e531 100644
--- a/Documentation/admin-guide/mm/numa_memory_policy.rst
+++ b/Documentation/admin-guide/mm/numa_memory_policy.rst@@ -245,6 +245,14 @@ MPOL_INTERLEAVED address range or file. During system boot up, the temporary interleaved system default policy works in this mode. +MPOL_PREFERRED_MANY + This mode specifies that the allocation should be attempted from the + nodemask specified in the policy. If that allocation fails, the kernel + will search other nodes, in order of increasing distance from the first + set bit in the nodemask based on information provided by the platform + firmware. It is similar to MPOL_PREFERRED with the main exception that + is an error to have an empty nodemask. + NUMA memory policy supports the following optional mode flags: MPOL_F_STATIC_NODES
@@ -253,10 +261,10 @@ MPOL_F_STATIC_NODES nodes changes after the memory policy has been defined. Without this flag, any time a mempolicy is rebound because of a - change in the set of allowed nodes, the node (Preferred) or - nodemask (Bind, Interleave) is remapped to the new set of - allowed nodes. This may result in nodes being used that were - previously undesired. + change in the set of allowed nodes, the preferred nodemask (Preferred + Many), preferred node (Preferred) or nodemask (Bind, Interleave) is + remapped to the new set of allowed nodes. This may result in nodes + being used that were previously undesired. With this flag, if the user-specified nodes overlap with the nodes allowed by the task's cpuset, then the memory policy is
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 93f8789758a7..d90247d6a71b 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c@@ -1463,12 +1463,7 @@ static inline int sanitize_mpol_flags(int *mode, unsigned short *flags) *flags = *mode & MPOL_MODE_FLAGS; *mode &= ~MPOL_MODE_FLAGS; - /* - * The check should be 'mode >= MPOL_MAX', but as 'prefer_many' - * is not fully implemented, don't permit it to be used for now, - * and the logic will be restored in following patch - */ - if ((unsigned int)(*mode) >= MPOL_PREFERRED_MANY) + if ((unsigned int)(*mode) >= MPOL_MAX) return -EINVAL; if ((*flags & MPOL_F_STATIC_NODES) && (*flags & MPOL_F_RELATIVE_NODES)) return -EINVAL;
--
2.7.4