Messages in this thread | | | Date | Thu, 28 Jan 2021 00:28:37 -0800 | From | Chris Goldsworthy <> | Subject | Re: [PATCH v4] fs/buffer.c: Revoke LRU when trying to drop buffers |
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On 2021-01-26 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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