On 12.03.21 10:03, David Hildenbrand wrote:
On 10.03.21 17:14, Minchan Kim wrote:
ffer_head LRU caches will be pinned and thus cannot be migrated.
This can prevent CMA allocations from succeeding, which are often used
on platforms with co-processors (such as a DSP) that can only use
physically contiguous memory. It can also prevent memory
hot-unplugging from succeeding, which involves migrating at least
MIN_MEMORY_BLOCK_SIZE bytes of memory, which ranges from 8 MiB to 1
GiB based on the architecture in use.
Actually, it's memory_block_size_bytes(), which can be even bigger
(IIRC, 128MiB..2 GiB on x86-64) that fails to get offlined. But that
will prevent bigger granularity (e.g., a whole DIMM) from getting unplugged.
Correspondingly, invalidate the BH LRU caches before a migration
starts and stop any buffer_head from being cached in the LRU caches,
until migration has finished.
Sounds sane to me.
Diving a bit into the code, I am wondering:
a) Are these buffer head pages marked as movable?
IOW, are they either PageLRU() or __PageMovable()?
b) How do these pages end up on ZONE_MOVABLE or MIGRATE_CMA?
I assume these pages come via
alloc_page_buffers()->alloc_buffer_head()->kmem_cache_zalloc(GFP_NOFS |
__GFP_ACCOUNT)
--
Thanks,
David / dhildenb
