| Re: [RFC][PATCH][3/4] Add reclaim support [message #10442 is a reply to message #10434] |
Mon, 19 February 2007 11:10   |
Andrew Morton
Messages: 127
Registered: December 2005
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Senior Member |
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On Mon, 19 Feb 2007 16:20:53 +0530 Balbir Singh <balbir@in.ibm.com> wrote:
> >> + * so, is the container over it's limit. Returns 1 if the container is above
> >> + * its limit.
> >> + */
> >> +int memctlr_mm_overlimit(struct mm_struct *mm, void *sc_cont)
> >> +{
> >> + struct container *cont;
> >> + struct memctlr *mem;
> >> + long usage, limit;
> >> + int ret = 1;
> >> +
> >> + if (!sc_cont)
> >> + goto out;
> >> +
> >> + read_lock(&mm->container_lock);
> >> + cont = mm->container;
> >> +
> >> + /*
> >> + * Regular reclaim, let it proceed as usual
> >> + */
> >> + if (!sc_cont)
> >> + goto out;
> >> +
> >> + ret = 0;
> >> + if (cont != sc_cont)
> >> + goto out;
> >> +
> >> + mem = memctlr_from_cont(cont);
> >> + usage = atomic_long_read(&mem->counter.usage);
> >> + limit = atomic_long_read(&mem->counter.limit);
> >> + if (limit && (usage > limit))
> >> + ret = 1;
> >> +out:
> >> + read_unlock(&mm->container_lock);
> >> + return ret;
> >> +}
> >
> > hm, I wonder how much additional lock traffic all this adds.
> >
>
> It's a read_lock() and most of the locks are read_locks
> which allow for concurrent access, until the container
> changes or goes away
read_lock isn't free, and I suspect we're calling this function pretty
often (every pagefault?) It'll be measurable on some workloads, on some
hardware.
It probably won't be terribly bad because each lock-taking is associated
with a clear_page(). But still, if there's any possibility of lightening
the locking up, now is the time to think about it.
> >> @@ -66,6 +67,9 @@ struct scan_control {
> >> int swappiness;
> >>
> >> int all_unreclaimable;
> >> +
> >> + void *container; /* Used by containers for reclaiming */
> >> + /* pages when the limit is exceeded */
> >> };
> >
> > eww. Why void*?
> >
>
> I did not want to expose struct container in mm/vmscan.c.
It's already there, via rmap.h
> An additional
> thought was that no matter what container goes in the field would be
> useful for reclaim.
Am having trouble parsing that sentence ;)
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