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SubjectRe: [PATCH] memcg: remove trylock_page_cgroup
On Tue, 21 Apr 2009 23:01:47 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Wed, 22 Apr 2009 13:41:08 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>
> > > I expect that it will reliably fail if the caller is running as
> > > SCHED_FIFO and the machine is single-CPU, or if we're trying to yield
> > > to a SCHED_OTHER task which is pinned to this CPU, etc. The cond_resched()
> > > won't work.
> > >
> > Hm, signal_pending() is supported now (so special user scan use alaram())
> > I used yield() before cond_resched() but I was told don't use it.
> > Should I replace cond_resched() with congestion_wait(HZ/10) or some ?
>
> msleep(1) would be typical. That can also be used to give a
> predictable number of seconds for the timeout.
>
> If 1 millisecond is too coarse then it's possible to sleep for much
> shorter intervals if the platform implements hi-res timers. We don't
> appear to have a handy interface to that (usleep, microsleep,
> nanosleep, etc?).
>
> And an attempt to sleep for 1us will fall back to 1/HZ if the platform
> doesn't implement hi-res timers, so that loop will need to be turned
> into a do {} while(!timer_after(jiffies, start))) thing. Probably it
> should be converted to that anyway, to be better behaved/predictable,
> etc.
>
I'm now consdiering to make this loop _short_ and call lru_add_drain_all()
when the loop finds a page is busy. (lru_add_drain_all() will sleep until
the end of keventd.) And yes, checking jiffies and do sleep if it seems
necessary.


I'll write some RFC today.

Thanks,
-Kame



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