On 2021-01-26 18:59, Matthew Wilcox wrote:
On Tue, Jan 26, 2021 at 02:59:17PM -0800, Minchan Kim wrote:
The release buffer_head in LRU is great improvement for migration
point of view.
A question:
Hey guys,
Can't we invalidate(e.g., invalidate_bh_lrus) bh_lru in migrate_prep
or
elsewhere when migration found the failure and is about to retry?
Migration has done such a way for other per-cpu stuffs for a long
time,
which would be more consistent with others and might be faster
sometimes
with reducing IPI calls for page.
Should lru_add_drain_all() also handle draining the buffer lru for all
callers? A quick survey ...
invalidate_bdev() already calls invalidate_bh_lrus()
compact_nodes() would probably benefit from the BH LRU being
invalidated
POSIX_FADV_DONTNEED would benefit if the underlying filesystem uses BHs
check_and_migrate_cma_pages() would benefit
khugepaged_do_scan() doesn't need it today
scan_get_next_rmap_item() looks like it only works on anon pages (?) so
doesn't need it
mem_cgroup_force_empty() probably needs it
mem_cgroup_move_charge() ditto
memfd_wait_for_pins() doesn't need it
shake_page() might benefit
offline_pages() would benefit
alloc_contig_range() would benefit
Seems like most would benefit and a few won't care. I think I'd lean
towards having lru_add_drain_all() call invalidate_bh_lrus(), just to
simplify things.
Doing this sounds like a good idea. We would still need a call to
invalidate_bh_lrus() inside of drop_buffers() in the event that we find
busy buffers, since they can be re-added back into the BH LRU - I
believe
it isn't until this point that a BH can't be added back into the BH LRU,
when we acquire the private_lock for the mapping:
https://elixir.bootlin.com/linux/v5.10.10/source/fs/buffer.c#L3240
Thanks,
Chris.
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