On Wed, Jan 27, 2021 at 02:59:22AM +0000, Matthew Wilcox wrote:

On Tue, Jan 26, 2021 at 02:59:17PM -0800, Minchan Kim wrote:

quoted

The release buffer_head in LRU is great improvement for migration
point of view.

A question: 

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.

Fair enough.