在 2020/6/21 上午7:08, Andrew Morton 写道:
> On Fri, 19 Jun 2020 16:33:38 +0800 Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx> wrote:
>
>> This is a new version which bases on linux-next, merged much suggestion
>> from Hugh Dickins, from compaction fix to less TestClearPageLRU and
>> comments reverse etc. Thank a lot, Hugh!
>>
>> Johannes Weiner has suggested:
>> "So here is a crazy idea that may be worth exploring:
>>
>> Right now, pgdat->lru_lock protects both PageLRU *and* the lruvec's
>> linked list.
>>
>> Can we make PageLRU atomic and use it to stabilize the lru_lock
>> instead, and then use the lru_lock only serialize list operations?
>
> I don't understand this sentence. How can a per-page flag stabilize a
> per-pgdat spinlock? Perhaps some additional description will help.
Hi Andrew,
Well, above comments miss a context, which lru_lock means new lru_lock on each
of memcg not the current per node lru_lock. Sorry!
Currently the lru bit changed under lru_lock, so isolate a page from lru just
need take lru_lock. New patch will change it with a atomic action alone from
lru_lock, so isolate a page need both actions: TestClearPageLRU and take the
lru_lock. like followings in isolate_lru_page():
The main reason for this comes from isolate_migratepages_block() in compaction.c
we have to take lru bit before lru lock, that serialized the page isolation in
memcg page charge/migration which will change page's lruvec and new lru_lock
in it. The current isolation just take lru lock directly which fails on guard
page's lruvec change(memcg change).
changes in isolate_lru_page():- if (PageLRU(page)) {
+ if (TestClearPageLRU(page)) {
pg_data_t *pgdat = page_pgdat(page);
struct lruvec *lruvec;
+ int lru = page_lru(page);
- spin_lock_irq(&pgdat->lru_lock);
+ get_page(page);
lruvec = mem_cgroup_page_lruvec(page, pgdat);
- if (PageLRU(page)) {
- int lru = page_lru(page);
- get_page(page);
- ClearPageLRU(page);
- del_page_from_lru_list(page, lruvec, lru);
- ret = 0;
- }
+ spin_lock_irq(&pgdat->lru_lock);
+ del_page_from_lru_list(page, lruvec, lru);
spin_unlock_irq(&pgdat->lru_lock);
+ ret = 0;
}
>
>>
>> Following Daniel Jordan's suggestion, I have run 208 'dd' with on 104
>> containers on a 2s * 26cores * HT box with a modefied case:
>> https://git.kernel.org/pub/scm/linux/kernel/git/wfg/vm-scalability.git/tree/case-lru-file-readtwice
>>
>> With this patchset, the readtwice performance increased about 80%
>> in concurrent containers.
>>
>> Thanks Hugh Dickins and Konstantin Khlebnikov, they both brought this
>> idea 8 years ago, and others who give comments as well: Daniel Jordan,
>> Mel Gorman, Shakeel Butt, Matthew Wilcox etc.
>>
>> Thanks for Testing support from Intel 0day and Rong Chen, Fengguang Wu,
>> and Yun Wang. Hugh Dickins also shared his kbuild-swap case. Thanks!
>>
>> ...
>>
>> 24 files changed, 500 insertions(+), 357 deletions(-)
>
> It's a large patchset and afaict the whole point is performance gain.
> 80% in one specialized test sounds nice, but is there a plan for more
> extensive quantification?
Once I got 5% aim7 performance gain on 16 cores machine, and about 20+%
readtwice performance gain. the performance gain is increased a lot following
larger cores.
Is there some suggestion for this?
>
> There isn't much sign of completed review activity here, so I'll go
> into hiding for a while.
>
Yes, it's relatively big. also much of change from comments part. :)
Anyway, thanks for look into!
Thanks
Alex
