Re: [RFC 2.6.11-rc2-mm2 0/7] mm: manual page migration -- overview II

[Ray Bryant <raybry@sgi.com>]

Andi Kleen wrote:

> 
> How about you add the va_start, va_end but only accept them 
> when pid is 0 (= current process). Otherwise enforce with EINVAL
> that they are both 0. This way you could map the
> shared object into the batch manager, migrate it there, then
> mark it somehow to not be migrated further, and then
> migrate the anonymous pages using migrate_pages(pid, ...) 
>

We'd have to use up a struct page flag (PG_MIGRATED?) to mark
the page as migrated to keep the call to migrate_pages() for
the anonymous pages from migrating the pages again.  Then we'd
have to have some way to clear PG_MIGRATED once all of the
migrate_pages() calls are complete (we can't have the anonymous
page migrate_pages() calls clear the flags, since the second
such call would find the flag clear and remigrate the pages
in the overlapping nodes case.)

How about ignoring the va_start and va_end values unless
either:

       pid == current->pid
   or  current->euid == 0 /* we're root */

I like the first check a bit better than checking for 0.  Are
there other system calls that follow that convention (e. g.
pid = 0 implies current?)

The second check lets a sufficiently responsible task manipulate
other tasks.  This task can choose to have the target tasks
suspended before it starts fussing with them.

> BTW it might be better to make va_end a size, just to be more
> symmetric with mlock,madvise,mmap et.al.
> 

Yes,.that's been pointed out to me before.  Let's make it so.

-- 
Best Regards,
Ray
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                   Ray Bryant
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raybry@sgi.com             raybry@austin.rr.com
The box said: "Requires Windows 98 or better",
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