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

[Brice Goglin <Brice.Goglin@inria.fr>]

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.

Brice



>
>> 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/
>>>
>

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