On 2024/2/15 15:06, Yu Zhao wrote: > On Wed, Feb 14, 2024 at 4:18 AM Chengming Zhou <chengming.zhou@xxxxxxxxx> wrote: >> >> On 2024/2/14 15:13, Yu Zhao wrote: >>> On Fri, Feb 9, 2024 at 6:00 AM <chengming.zhou@xxxxxxxxx> wrote: >>>> >>>> From: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx> >>>> >>>> All LRU move interfaces have a problem that it has no effect if the >>>> folio is isolated from LRU (in cpu batch or isolated by shrinker). >>>> Since it can't move/change folio LRU status when it's isolated, mostly >>>> just clear the folio flag and do nothing in this case. >>>> >>>> In our case, a written back and reclaimable folio won't be rotated to >>>> the tail of inactive list, since it's still in cpu lru_add batch. It >>>> may cause the delayed reclaim of this folio and evict other folios. >>>> >>>> This patch changes to queue the reclaimable folio to cpu rotate batch >>>> even when !folio_test_lru(), hoping it will likely be handled after >>>> the lru_add batch which will put folio on the LRU list first, so >>>> will be rotated to the tail successfully when handle rotate batch. >>>> >>>> Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx> >>> >>> I don't think the analysis is correct. IIRC, writeback from non >>> reclaim paths doesn't require isolation and the reclaim path doesn't >>> use struct folio_batch lru_add. >> >> Ah, my bad, I forgot to mention the important context in the message: >> >> This is not from the normal reclaim context, it's from zswap writeback >> reclaim context, which will first set PG_reclaim flag, then submit the >> async writeback io. >> >> If the writeback io complete fast enough, folio_rotate_reclaimable() >> will be called before that folio put on LRU list (it still in the local >> lru_add batch, so it's somewhat like isolated too) >> >>> >>> Did you see any performance improvements with this patch? In general, >>> this kind of patches should have performance numbers to show it really >>> helps (not just in theory). >> >> Right, there are some improvements, the numbers are put in cover letter. >> But this solution is not good enough, just RFC for discussion. :) >> >> mm-unstable-hot zswap-lru-reclaim >> real 63.34 62.72 >> user 1063.20 1060.30 >> sys 272.04 256.14 >> workingset_refault_anon 2103297.00 1788155.80 >> workingset_refault_file 28638.20 39249.40 >> workingset_activate_anon 746134.00 695435.40 >> workingset_activate_file 4344.60 4255.80 >> workingset_restore_anon 653163.80 605315.60 >> workingset_restore_file 1079.00 883.00 >> workingset_nodereclaim 0.00 0.00 >> pgscan 12971305.60 12730331.20 >> pgscan_kswapd 0.00 0.00 >> pgscan_direct 12971305.60 12730331.20 >> pgscan_khugepaged 0.00 0.00 >> >>> >>> My guess is that you are hitting this problem [1]. >>> >>> [1] https://lore.kernel.org/linux-mm/20221116013808.3995280-1-yuzhao@xxxxxxxxxx/ >> >> Right, I just see it, it's the same problem. The only difference is that >> in your case the folio is isolated by shrinker, in my case, the folio is >> in cpu lru_add batch. Anyway, the result is the same, that folio can't be >> rotated successfully when writeback complete. > > In that case, a better solution would be to make lru_add add > (_reclaim() && !_dirty() && !_writeback()) folios at the tail. > (_rotate() needs to leave _reclaim() set if it fails to rotate.) Right, this is a solution. But PG_readahead is alias of PG_reclaim, I'm afraid this would rotate readahead folio to the inactive tail.
