Messages in this thread | | | From | David Hildenbrand <> | Subject | Re: [PATCH v3 3/3] mm: fs: Invalidate BH LRU during page migration | Date | Fri, 12 Mar 2021 10:33:48 +0100 |
| |
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
| |