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SubjectRe: [PATCH] 2.6.25-rc3-mm1 - Mempolicy - update stale documentation and comments
On (04/03/08 15:20), Lee Schermerhorn didst pronounce:
> Was Re: [PATCH 5/6] Filter based on a nodemask as well as a gfp_mask
>
> On Thu, 2008-02-28 at 23:01 -0600, Paul Jackson wrote:
> > Mel wrote:
> > > A positive benefit of
> > > this is that allocations using MPOL_BIND now use the local-node-ordered
> > > zonelist instead of a custom node-id-ordered zonelist.
> >
> > Could you update the now obsolete documentation (perhaps just delete
> > the no longer correct remark):
> >
> > Documentation/vm/numa_memory_policy.txt:
> >
> > MPOL_BIND: This mode specifies that memory must come from the
> > set of nodes specified by the policy.
> >
> > The memory policy APIs do not specify an order in which the nodes
> > will be searched. However, unlike "local allocation", the Bind
> > policy does not consider the distance between the nodes. Rather,
> > allocations will fallback to the nodes specified by the policy in
> > order of numeric node id. Like everything in Linux, this is subject
> > to change.
> >
>
> How's this:
>
> PATCH Mempolicy: update documentation and comments
>
> Address stale comments and numa_memory_policy.txt discussion
> based on Mel Gorman's changes to page allocation zonelist handling.
>
> Specifically: mpol_free() and mpol_copy() no longer need to deal
> with a custom zonelist for MPOL_BIND policy, and MPOL_BIND now
> allocates memory from the nearest node with available memory in the
> specified nodemask.
>
> In "fixing" the mpol_free() and mpol_copy() comments in mempolicy.h,
> I wanted to replace them with something, rather than just deleting
> them. So, I described the reference counting. Not directly related
> to the zonelist changes, but useful, IMO.
>
> Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
>

Looks great.

Acked-by: Mel Gorman <mel@csn.ul.ie>

> Documentation/vm/numa_memory_policy.txt | 11 +++--------
> include/linux/mempolicy.h | 8 +++++---
> 2 files changed, 8 insertions(+), 11 deletions(-)
>
> Index: linux-2.6.25-rc3-mm1/Documentation/vm/numa_memory_policy.txt
> ===================================================================
> --- linux-2.6.25-rc3-mm1.orig/Documentation/vm/numa_memory_policy.txt 2008-01-24 17:58:37.000000000 -0500
> +++ linux-2.6.25-rc3-mm1/Documentation/vm/numa_memory_policy.txt 2008-03-04 14:44:51.000000000 -0500
> @@ -182,14 +182,9 @@ Components of Memory Policies
> The Default mode does not use the optional set of nodes.
>
> MPOL_BIND: This mode specifies that memory must come from the
> - set of nodes specified by the policy.
> -
> - The memory policy APIs do not specify an order in which the nodes
> - will be searched. However, unlike "local allocation", the Bind
> - policy does not consider the distance between the nodes. Rather,
> - allocations will fallback to the nodes specified by the policy in
> - order of numeric node id. Like everything in Linux, this is subject
> - to change.
> + set of nodes specified by the policy. Memory will be allocated from
> + the node in the set with sufficient free memory that is closest to
> + the node where the allocation takes place.
>
> MPOL_PREFERRED: This mode specifies that the allocation should be
> attempted from the single node specified in the policy. If that
> Index: linux-2.6.25-rc3-mm1/include/linux/mempolicy.h
> ===================================================================
> --- linux-2.6.25-rc3-mm1.orig/include/linux/mempolicy.h 2008-03-04 14:19:06.000000000 -0500
> +++ linux-2.6.25-rc3-mm1/include/linux/mempolicy.h 2008-03-04 14:38:29.000000000 -0500
> @@ -54,11 +54,13 @@ struct mm_struct;
> * mmap_sem.
> *
> * Freeing policy:
> - * When policy is MPOL_BIND v.zonelist is kmalloc'ed and must be kfree'd.
> - * All other policies don't have any external state. mpol_free() handles this.
> + * Mempolicy objects are reference counted. A mempolicy will be freed when
> + * mpol_free() decrements the reference count to zero.
> *
> * Copying policy objects:
> - * For MPOL_BIND the zonelist must be always duplicated. mpol_clone() does this.
> + * mpol_copy() allocates a new mempolicy and copies the specified mempolicy
> + * to the new storage. The reference count of the new object is initialized
> + * to 1, representing the caller of mpol_copy().
> */
> struct mempolicy {
> atomic_t refcnt;
>
>

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab


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