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get_mempolicy.2, set_mempolicy: Policy is per thread, not per process 

set/get_mempolicy manpages say that the memory allocation
policy is per process while reading the code and testing shows
that it's actually per thread.  Here's a quick fix, which may
need to be improved to better explain that we're allocating
in the context of a thread within a process address space.

Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Brice Goglin 2015-04-30 12:31:09 +02:00 committed by Michael Kerrisk
parent e23f2a23cd
commit 856778162b
2 changed files with 25 additions and 25 deletions
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22
man2/get_mempolicy.2
View File

@ -26,7 +26,7 @@
.\" .\"
.TH GET_MEMPOLICY 2 2008-08-15 Linux "Linux Programmer's Manual" .TH GET_MEMPOLICY 2 2008-08-15 Linux "Linux Programmer's Manual"
.SH NAME .SH NAME
get_mempolicy \- retrieve NUMA memory policy for a process get_mempolicy \- retrieve NUMA memory policy for a thread
.SH SYNOPSIS .SH SYNOPSIS
.B "#include <numaif.h>" .B "#include <numaif.h>"
.nf .nf
@ -39,19 +39,19 @@ Link with \fI\-lnuma\fP.
.fi .fi
.SH DESCRIPTION .SH DESCRIPTION
.BR get_mempolicy () .BR get_mempolicy ()
retrieves the NUMA policy of the calling process or of a memory address, retrieves the NUMA policy of the calling thread or of a memory address,
depending on the setting of depending on the setting of
.IR flags . .IR flags .
A NUMA machine has different A NUMA machine has different
memory controllers with different distances to specific CPUs. memory controllers with different distances to specific CPUs.
The memory policy defines from which node memory is allocated for The memory policy defines from which node memory is allocated for
the process. the thread.
If If
.I flags .I flags
is specified as 0, is specified as 0,
then information about the calling process's default policy then information about the calling thread's default policy
(as set by (as set by
.BR set_mempolicy (2)) .BR set_mempolicy (2))
is returned. is returned.
@ -59,7 +59,7 @@ The policy returned
.RI [ mode .RI [ mode
and and
.IR nodemask ] .IR nodemask ]
may be used to restore the process's policy to its state at may be used to restore the thread's policy to its state at
the time of the call to the time of the call to
.BR get_mempolicy () .BR get_mempolicy ()
using using
@ -72,7 +72,7 @@ specifies
(available since Linux 2.6.24), the (available since Linux 2.6.24), the
.I mode .I mode
argument is ignored and the set of nodes [memories] that the argument is ignored and the set of nodes [memories] that the
process is allowed to specify in subsequent calls to thread is allowed to specify in subsequent calls to
.BR mbind (2) .BR mbind (2)
or or
.BR set_mempolicy (2) .BR set_mempolicy (2)
@ -94,7 +94,7 @@ specifies
then information is returned about the policy governing the memory then information is returned about the policy governing the memory
address given in address given in
.IR addr . .IR addr .
This policy may be different from the process's default policy if This policy may be different from the thread's default policy if
.BR mbind (2) .BR mbind (2)
or one of the helper functions described in or one of the helper functions described in
.BR numa (3) .BR numa (3)
@ -135,7 +135,7 @@ is allocated into the location pointed to by
.IR mode . .IR mode .
If no page has yet been allocated for the specified address, If no page has yet been allocated for the specified address,
.BR get_mempolicy () .BR get_mempolicy ()
will allocate a page as if the process had performed a read will allocate a page as if the thread had performed a read
[load] access to that address, and return the ID of the node [load] access to that address, and return the ID of the node
where that page was allocated. where that page was allocated.
@ -145,7 +145,7 @@ specifies
.BR MPOL_F_NODE , .BR MPOL_F_NODE ,
but not but not
.BR MPOL_F_ADDR , .BR MPOL_F_ADDR ,
and the process's current policy is and the thread's current policy is
.BR MPOL_INTERLEAVE , .BR MPOL_INTERLEAVE ,
then then
.BR get_mempolicy () .BR get_mempolicy ()
@ -153,7 +153,7 @@ will return in the location pointed to by a non-NULL
.I mode .I mode
argument, argument,
the node ID of the next node that will be used for the node ID of the next node that will be used for
interleaving of internal kernel pages allocated on behalf of the process. interleaving of internal kernel pages allocated on behalf of the thread.
.\" Note: code returns next interleave node via 'mode' argument -Lee Schermerhorn .\" Note: code returns next interleave node via 'mode' argument -Lee Schermerhorn
These allocations include pages for memory-mapped files in These allocations include pages for memory-mapped files in
process memory ranges mapped using the process memory ranges mapped using the
@ -214,7 +214,7 @@ specified
.B MPOL_F_NODE .B MPOL_F_NODE
but not but not
.B MPOL_F_ADDR .B MPOL_F_ADDR
and the current process policy is not and the current thread policy is not
.BR MPOL_INTERLEAVE . .BR MPOL_INTERLEAVE .
Or, Or,
.I flags .I flags

28
man2/set_mempolicy.2
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@ -26,7 +26,7 @@
.\" .\"
.TH SET_MEMPOLICY 2 2014-05-28 Linux "Linux Programmer's Manual" .TH SET_MEMPOLICY 2 2014-05-28 Linux "Linux Programmer's Manual"
.SH NAME .SH NAME
set_mempolicy \- set default NUMA memory policy for a process and its children set_mempolicy \- set default NUMA memory policy for a thread and its children
.SH SYNOPSIS .SH SYNOPSIS
.nf .nf
.B "#include <numaif.h>" .B "#include <numaif.h>"
@ -38,7 +38,7 @@ Link with \fI\-lnuma\fP.
.fi .fi
.SH DESCRIPTION .SH DESCRIPTION
.BR set_mempolicy () .BR set_mempolicy ()
sets the NUMA memory policy of the calling process, sets the NUMA memory policy of the calling thread,
which consists of a policy mode and zero or more nodes, which consists of a policy mode and zero or more nodes,
to the values specified by the to the values specified by the
.IR mode , .IR mode ,
@ -50,28 +50,28 @@ arguments.
A NUMA machine has different A NUMA machine has different
memory controllers with different distances to specific CPUs. memory controllers with different distances to specific CPUs.
The memory policy defines from which node memory is allocated for The memory policy defines from which node memory is allocated for
the process. the thread.
This system call defines the default policy for the process. This system call defines the default policy for the thread.
The process policy governs allocation of pages in the process's The thread policy governs allocation of pages in the process's
address space outside of memory ranges address space outside of memory ranges
controlled by a more specific policy set by controlled by a more specific policy set by
.BR mbind (2). .BR mbind (2).
The process default policy also controls allocation of any pages for The thread default policy also controls allocation of any pages for
memory-mapped files mapped using the memory-mapped files mapped using the
.BR mmap (2) .BR mmap (2)
call with the call with the
.B MAP_PRIVATE .B MAP_PRIVATE
flag and that are only read [loaded] from by the process flag and that are only read [loaded] from by the thread
and of memory-mapped files mapped using the and of memory-mapped files mapped using the
.BR mmap (2) .BR mmap (2)
call with the call with the
.B MAP_SHARED .B MAP_SHARED
flag, regardless of the access type. flag, regardless of the access type.
The policy is applied only when a new page is allocated The policy is applied only when a new page is allocated
for the process. for the thread.
For anonymous memory this is when the page is first For anonymous memory this is when the page is first
touched by the application. touched by the thread.
The The
.I mode .I mode
@ -154,7 +154,7 @@ cpuset context includes one or more of the nodes specified by
The The
.B MPOL_DEFAULT .B MPOL_DEFAULT
mode specifies that any nondefault process memory policy be removed, mode specifies that any nondefault thread memory policy be removed,
so that the memory policy "falls back" to the system default policy. so that the memory policy "falls back" to the system default policy.
The system default policy is "local allocation"\(emthat is, The system default policy is "local allocation"\(emthat is,
allocate memory on the node of the CPU that triggered the allocation. allocate memory on the node of the CPU that triggered the allocation.
@ -211,9 +211,9 @@ arguments specify the empty set, then the policy
specifies "local allocation" specifies "local allocation"
(like the system default policy discussed above). (like the system default policy discussed above).
The process memory policy is preserved across an The thread memory policy is preserved across an
.BR execve (2), .BR execve (2),
and is inherited by child processes created using and is inherited by child threads created using
.BR fork (2) .BR fork (2)
or or
.BR clone (2). .BR clone (2).
@ -279,9 +279,9 @@ system call was added to the Linux kernel in version 2.6.7.
.SH CONFORMING TO .SH CONFORMING TO
This system call is Linux-specific. This system call is Linux-specific.
.SH NOTES .SH NOTES
Process policy is not remembered if the page is swapped out. Memory policy is not remembered if the page is swapped out.
When such a page is paged back in, it will use the policy of When such a page is paged back in, it will use the policy of
the process or memory range that is in effect at the time the the thread or memory range that is in effect at the time the
page is allocated. page is allocated.
For information on library support, see For information on library support, see