On Thu, Jan 28, 2021 at 12:28:37AM -0800, Chris Goldsworthy wrote: > 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 I am not sure it's good deal considering IPI overhead per page release at worst case. A idea is to disable bh_lrus in migrate_prep and enable it when migration is done(need to introduce "migrate_done". It's similar approach with marking pageblock MIGRATE_ISOLATE to disable pcp during the migration.
