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SubjectRe: [PATCH 07/19] mm/mpol: Add MPOL_MF_NOOP
On Tue, Jul 31, 2012 at 09:12:11PM +0200, Peter Zijlstra wrote:
> From: Lee Schermerhorn <lee.schermerhorn@hp.com>
>
> This patch augments the MPOL_MF_LAZY feature by adding a "NOOP"
> policy to mbind(). When the NOOP policy is used with the 'MOVE
> and 'LAZY flags, mbind() [check_range()] will walk the specified
> range and unmap eligible pages so that they will be migrated on
> next touch.
>
> This allows an application to prepare for a new phase of operation
> where different regions of shared storage will be assigned to
> worker threads, w/o changing policy. Note that we could just use
> "default" policy in this case. However, this also allows an
> application to request that pages be migrated, only if necessary,
> to follow any arbitrary policy that might currently apply to a
> range of pages, without knowing the policy, or without specifying
> multiple mbind()s for ranges with different policies.

This is a new kapi change. I could hardly understand the above so I
wonder how long it will take before userland programmers will be
familiar with MPOL_NOOP to actually use it in most apps? Could you
just enable/disable your logics using a sysfs knob instead?

enabling/disabling sched-numa is something an admin can easily do with
a sysfs control, patching and rebuilding a proprietary app using mbind
calls, no way, especially if the app is proprietary.

>
> Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> ---
> include/linux/mempolicy.h | 1 +
> mm/mempolicy.c | 8 ++++----
> 2 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
> index 87fabfa..668311a 100644
> --- a/include/linux/mempolicy.h
> +++ b/include/linux/mempolicy.h
> @@ -21,6 +21,7 @@ enum {
> MPOL_BIND,
> MPOL_INTERLEAVE,
> MPOL_LOCAL,
> + MPOL_NOOP, /* retain existing policy for range */
> MPOL_MAX, /* always last member of enum */
> };
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 4fba5f2..251ef31 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -251,10 +251,10 @@ static struct mempolicy *mpol_new(unsigned short mode, unsigned short flags,
> pr_debug("setting mode %d flags %d nodes[0] %lx\n",
> mode, flags, nodes ? nodes_addr(*nodes)[0] : -1);
>
> - if (mode == MPOL_DEFAULT) {
> + if (mode == MPOL_DEFAULT || mode == MPOL_NOOP) {
> if (nodes && !nodes_empty(*nodes))
> return ERR_PTR(-EINVAL);
> - return NULL; /* simply delete any existing policy */
> + return NULL;
> }
> VM_BUG_ON(!nodes);
>
> @@ -1069,7 +1069,7 @@ static long do_mbind(unsigned long start, unsigned long len,
> if (start & ~PAGE_MASK)
> return -EINVAL;
>
> - if (mode == MPOL_DEFAULT)
> + if (mode == MPOL_DEFAULT || mode == MPOL_NOOP)
> flags &= ~MPOL_MF_STRICT;
>
> len = (len + PAGE_SIZE - 1) & PAGE_MASK;
> @@ -1121,7 +1121,7 @@ static long do_mbind(unsigned long start, unsigned long len,
> flags | MPOL_MF_INVERT, &pagelist);
>
> err = PTR_ERR(vma); /* maybe ... */
> - if (!IS_ERR(vma))
> + if (!IS_ERR(vma) && mode != MPOL_NOOP)
> err = mbind_range(mm, start, end, new);
>
> if (!err) {
> --
> 1.7.2.3
>
>
>
> --
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