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

["Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>]

Hi Andi,

On 05/06/2015 02:57 PM, Andi Kleen wrote:
> 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 ?

No, it doesn't seem to be quite that. Brice, can you say a little more here?

> 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.

Okay -- I'll await further input from Brice, and then apply.

Cheers,

Michael


>> 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/
>>
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

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