Re: needed lru_add_drain_all() change

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(2012/06/28 15:23), KOSAKI Motohiro wrote:
On Tue, Jun 26, 2012 at 5:37 PM, Andrew Morton
<akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
https://bugzilla.kernel.org/show_bug.cgi?id=43811

lru_add_drain_all() uses schedule_on_each_cpu().  But
schedule_on_each_cpu() hangs if a realtime thread is spinning, pinned
to a CPU.  There's no intention to change the scheduler behaviour, so I
think we should remove schedule_on_each_cpu() from the kernel.

The biggest user of schedule_on_each_cpu() is lru_add_drain_all().

Does anyone have any thoughts on how we can do this?  The obvious
approach is to declare these:

static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS], lru_add_pvecs);
static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs);

to be irq-safe and use on_each_cpu().  lru_rotate_pvecs is already
irq-safe and converting lru_add_pvecs and lru_deactivate_pvecs looks
pretty simple.

Thoughts?

I agree.

But i hope more. In these days, we have plenty lru_add_drain_all()
callsite. So,
i think we should remove struct pagevec and should aim migration aware new
batch mechanism. maybe. This also improve compaction success rate.


migration-aware means an framework which isolate_xxxx_page() can work with ?
To do that, we need to know which object points to the page. Hmm. Do you have
anyidea ?

-Kame








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