On 11/26/20 4:12 AM, Alex Shi wrote:
在 2020/11/25 下午11:38, Vlastimil Babka 写道:
On 11/20/20 9:27 AM, Alex Shi wrote:
The current relock logical will change lru_lock when found a new
lruvec, so if 2 memcgs are reading file or alloc page at same time,
they could hold the lru_lock alternately, and wait for each other for
fairness attribute of ticket spin lock.
This patch will sort that all lru_locks and only hold them once in
above scenario. That could reduce fairness waiting for lock reget.
Than, vm-scalability/case-lru-file-readtwice could get ~5% performance
gain on my 2P*20core*HT machine.
Hm, once you sort the pages like this, it's a shame not to splice them instead of more list_del() + list_add() iterations. update_lru_size() could be also called once?
Yes, looks it's a good idea to use splice instead of list_del/add, but pages
may on different lru list in a same lruvec, and also may come from different
zones. That could involve 5 cycles for different lists, and more for zones...
Hmm, zones wouldn't affect splicing (there's a per-node lru these days), but
would affect accounting. And yeah, there are 5 lru lists, and we probably need
to be under lru lock to stabilize where a page belongs, so pre-sorting without
lock wouldn't be safe? Bummer.
I give up the try.
