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

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

Hi Brice,

On 05/06/2015 06:32 PM, Brice Goglin wrote:
> Le 06/05/2015 18:28, Michael Kerrisk (man-pages) a ecrit :
>> 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?
> 
> It's pretty much s/process/thread/ when process means "group of
> threads". When process is used for "address space", I didn't change much.

Okay. I've applied this patch. Thanks!

Thanks,

Michael


>>> 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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