Messages in this thread | | | Date | Thu, 28 Jan 2021 10:43:38 -0800 | From | Chris Goldsworthy <> | Subject | Re: [PATCH v4] fs/buffer.c: Revoke LRU when trying to drop buffers |
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On 2021-01-28 09:08, Minchan Kim wrote: > 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.
I'll try creating that mechanism then for the BH LRU, and will come back with a patch that does the invalidate in lru_add_drain_all().
Thanks Matthew and Minchan for the feedback!
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