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)
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
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