Re: Handling NUMA page migration

[Robin Holt <holt@sgi.com>]

This is probably more appropriate to be directed at the linux-mm
mailing list.

On Tue, Jun 04, 2013 at 09:22:10AM +0200, Frank Mehnert wrote:
> Hi,
> 
> our memory management on Linux hosts conflicts with NUMA page migration.
> I assume this problem existed for a longer time but Linux 3.8 introduced
> automatic NUMA page balancing which makes the problem visible on
> multi-node hosts leading to kernel oopses.
> 
> NUMA page migration means that the physical address of a page changes.
> This is fatal if the application assumes that this never happens for
> that page as it was supposed to be pinned.
> 
> We have two kind of pinned memory:
> 
> A) 1. allocate memory in userland with mmap()
>    2. madvise(MADV_DONTFORK)
>    3. pin with get_user_pages().
>    4. flush dcache_page()
>    5. vm_flags |= (VM_DONTCOPY | VM_LOCKED)
>       (resulting flags are VM_MIXEDMAP | VM_DONTDUMP | VM_DONTEXPAND |
>        VM_DONTCOPY | VM_LOCKED | 0xff)

I don't think this type of allocation should be affected.  The
get_user_pages() call should elevate the pages reference count which
should prevent migration from completing.  I would, however, wait for
a more definitive answer.

> B) 1. allocate memory with alloc_pages()
>    2. SetPageReserved()
>    3. vm_mmap() to allocate a userspace mapping
>    4. vm_insert_page()
>    5. vm_flags |= (VM_DONTEXPAND | VM_DONTDUMP)
>       (resulting flags are VM_MIXEDMAP | VM_DONTDUMP | VM_DONTEXPAND | 0xff)
> 
> At least the memory allocated like B) is affected by automatic NUMA page
> migration. I'm not sure about A).
> 
> 1. How can I prevent automatic NUMA page migration on this memory?
> 2. Can NUMA page migration also be handled on such kind of memory without
>    preventing migration?
> 
> Thanks,
> 
> Frank
> -- 
> Dr.-Ing. Frank Mehnert | Software Development Director, VirtualBox
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