Messages in this thread | | | Subject | Re: [PATCH v13 00/18] per memcg lru lock | From | Alex Shi <> | Date | Sun, 21 Jun 2020 23:44:47 +0800 |
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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@linux.alibaba.com> 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
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