Re: [PATCH] set/get_mempolicy.2: policy is per thread, not per process

[Andi Kleen <andi@firstfloor.org>]

On Wed, May 06, 2015 at 02:31:58PM +0200, Michael Kerrisk (man-pages) wrote:
> Hi Andi,
> 
> Brice's patch seems broadly okay to me, but you originally wrote the
> pages, so I'd be happy if you could comment. Could you take a look please?

Just s/process/thread/g ?

The distinction between process and thread is fuzzy in Linux of course,
but i suppose it matches the user's terms better.

Fine for me.

-Andi

> 
> Cheers,
> 
> Michael
> 
> 
> On 04/30/2015 12:31 PM, Brice Goglin wrote:
> > Hello,
> > 
> > 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.
> > 
> > Brice
> >  
> > 
> > 
> > 
> > 
> > 
> > set/get_mempolicy.2: policy is per thread, not per process
> > 
> > Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>
> > 
> > diff --git a/man2/get_mempolicy.2 b/man2/get_mempolicy.2
> > index a17c0f3..c0e9639 100644
> > --- a/man2/get_mempolicy.2
> > +++ b/man2/get_mempolicy.2
> > @@ -26,7 +26,7 @@
> >  .\"
> >  .TH GET_MEMPOLICY 2 2008-08-15 Linux "Linux Programmer's Manual"
> >  .SH NAME
> > -get_mempolicy \- retrieve NUMA memory policy for a process
> > +get_mempolicy \- retrieve NUMA memory policy for a thread
> >  .SH SYNOPSIS
> >  .B "#include <numaif.h>"
> >  .nf
> > @@ -39,19 +39,19 @@ Link with \fI\-lnuma\fP.
> >  .fi
> >  .SH DESCRIPTION
> >  .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
> >  .IR flags .
> >  
> >  A NUMA machine has different
> >  memory controllers with different distances to specific CPUs.
> >  The memory policy defines from which node memory is allocated for
> > -the process.
> > +the thread.
> >  
> >  If
> >  .I flags
> >  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
> >  .BR set_mempolicy (2))
> >  is returned.
> > @@ -59,7 +59,7 @@ The policy returned
> >  .RI [ mode
> >  and
> >  .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
> >  .BR get_mempolicy ()
> >  using
> > @@ -72,7 +72,7 @@ specifies
> >  (available since Linux 2.6.24), the
> >  .I mode
> >  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)
> >  or
> >  .BR set_mempolicy (2)
> > @@ -94,7 +94,7 @@ specifies
> >  then information is returned about the policy governing the memory
> >  address given in
> >  .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)
> >  or one of the helper functions described in
> >  .BR numa (3)
> > @@ -135,7 +135,7 @@ is allocated into the location pointed to by
> >  .IR mode .
> >  If no page has yet been allocated for the specified address,
> >  .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
> >  where that page was allocated.
> >  
> > @@ -145,7 +145,7 @@ specifies
> >  .BR MPOL_F_NODE ,
> >  but not
> >  .BR MPOL_F_ADDR ,
> > -and the process's current policy is
> > +and the thread's current policy is
> >  .BR MPOL_INTERLEAVE ,
> >  then
> >  .BR get_mempolicy ()
> > @@ -153,7 +153,7 @@ will return in the location pointed to by a non-NULL
> >  .I mode
> >  argument,
> >  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
> >  These allocations include pages for memory-mapped files in
> >  process memory ranges mapped using the
> > @@ -214,7 +214,7 @@ specified
> >  .B MPOL_F_NODE
> >  but not
> >  .B MPOL_F_ADDR
> > -and the current process policy is not
> > +and the current thread policy is not
> >  .BR MPOL_INTERLEAVE .
> >  Or,
> >  .I flags
> > diff --git a/man2/set_mempolicy.2 b/man2/set_mempolicy.2
> > index 9d7d1de..f5169da 100644
> > --- a/man2/set_mempolicy.2
> > +++ b/man2/set_mempolicy.2
> > @@ -26,7 +26,7 @@
> >  .\"
> >  .TH SET_MEMPOLICY 2 2014-05-28 Linux "Linux Programmer's Manual"
> >  .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
> >  .nf
> >  .B "#include <numaif.h>"
> > @@ -38,7 +38,7 @@ Link with \fI\-lnuma\fP.
> >  .fi
> >  .SH DESCRIPTION
> >  .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,
> >  to the values specified by the
> >  .IR mode ,
> > @@ -50,28 +50,28 @@ arguments.
> >  A NUMA machine has different
> >  memory controllers with different distances to specific CPUs.
> >  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.
> > -The process policy governs allocation of pages in the process's
> > +This system call defines the default policy for the thread.
> > +The thread policy governs allocation of pages in the process's
> >  address space outside of memory ranges
> >  controlled by a more specific policy set by
> >  .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
> >  .BR mmap (2)
> >  call with the
> >  .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
> >  .BR mmap (2)
> >  call with the
> >  .B MAP_SHARED
> >  flag, regardless of the access type.
> >  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
> > -touched by the application.
> > +touched by the thread.
> >  
> >  The
> >  .I mode
> > @@ -154,7 +154,7 @@ cpuset context includes one or more of the nodes specified by
> >  
> >  The
> >  .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.
> >  The system default policy is "local allocation"\(emthat is,
> >  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"
> >  (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),
> > -and is inherited by child processes created using
> > +and is inherited by child threads created using
> >  .BR fork (2)
> >  or
> >  .BR clone (2).
> > @@ -279,9 +279,9 @@ system call was added to the Linux kernel in version 2.6.7.
> >  .SH CONFORMING TO
> >  This system call is Linux-specific.
> >  .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
> > -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.
> >  
> >  For information on library support, see
> > 
> > 
> 
> 
> -- 
> Michael Kerrisk
> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
> Linux/UNIX System Programming Training: http://man7.org/training/
> 

-- 
ak@linux.intel.com -- Speaking for myself only.

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