Gerald Schaefer wrote:

On Mon, 2008-07-07 at 10:09 -0500, Christoph Lameter wrote:

quoted

This will extend the number of pages that are migratable and lead to strange
semantics in the NUMA case. There suddenly vma_is migratable will forbid hotplug
to migrate certain pages. 

I think we need two functions:

vma_migratable()	General migratability

vma_policy_migratable()	Migratable under NUMA policies.

Nothing will change here for the NUMA case, this is all about making it
compile w/o NUMA and with MIGRATION. What new strange semantics do you mean?
BTW, the latest patch in this thread will not touch vma_migratable() anymore,
I haven't read your mail before, sorry.

Ahh. Okay. However, we may still want a function that tells us if the pages in a vma
are migratable in general (independent of policies). The current vma_migratable function
tell you if the pages in a vma were placed according to a NUMA memory policy and should be migrated for NUMA locality optimizations.

quoted

That wont work since the migrate function takes a nodemask! The point of
the function is to move memory from node to node which is something that you
*cannot* do in a non NUMA configuration. So leave this chunk out.

Right, but I noticed that this function definition was needed to make it
compile with MIGRATION and w/o NUMA, although it would never be called in
non-NUMA config.

How does the compile break? It may be better to fix this where the function
is used.

A better solution would probably be to put migrate_vmas(), the only caller
of vm_ops->migrate(), inside '#ifdef CONFIG_NUMA', because it will only be
called from NUMA-only mm/mempolicy.c. Does that sound reasonable?

That sounds right.
 

quoted

Hmmm... Okay. I tried to make MIGRATION as independent of CONFIG_NUMA as possible so hopefully this will work.

Umm, it doesn't compile with MIGRATION and w/o NUMA, which was the reason
for this patch, because of the policy_zone reference in vma_migratable()
and the missing vm_ops->migrate() function.

Right. I did not have a use case for !NUMA when I wrote the code. So you now need to
fix the minor bits that break.

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