Re: [PATCH] mm: do not drain pagevecs for mlock

[KOSAKI Motohiro]

(1/6/12 1:46 AM), Tao Ma wrote:
> On 01/06/2012 02:33 PM, KOSAKI Motohiro wrote:
> > (1/6/12 1:30 AM), Tao Ma wrote:
> > > On 01/06/2012 02:18 PM, KOSAKI Motohiro wrote:
> > > > 2012/1/6 Tao Ma<tm@xxxxxx>:
> > > > > Hi Kosaki,
> > > > > On 12/30/2011 06:07 PM, KOSAKI Motohiro wrote:
> > > > > > > > Because your test program is too artificial. 20sec/100000times =
> > > > > > > > 200usec. And your
> > > > > > > > program repeat mlock and munlock the exact same address. so, yes, if
> > > > > > > > lru_add_drain_all() is removed, it become near no-op. but it's
> > > > > > > > worthless comparision.
> > > > > > > > none of any practical program does such strange mlock usage.
> > > > > > > yes, I should say it is artificial. But mlock did cause the
> > > > > > > problem in
> > > > > > > our product system and perf shows that the mlock uses the system time
> > > > > > > much more than others. That's the reason we created this program
> > > > > > > to test
> > > > > > > whether mlock really sucks. And we compared the result with
> > > > > > > rhel5(2.6.18) which runs much much faster.
> > > > > > >
> > > > > > > And from the commit log you described, we can remove
> > > > > > > lru_add_drain_all
> > > > > > > safely here, so why add it? At least removing it makes mlock much
> > > > > > > faster
> > > > > > > compared to the vanilla kernel.
> > > > > >
> > > > > > If we remove it, we lose to a test way of mlock. "Memlocked" field of
> > > > > > /proc/meminfo
> > > > > > show inaccurate number very easily. So, if 200usec is no avoidable,
> > > > > > I'll ack you.
> > > > > > But I'm not convinced yet.
> > > > > Do you find something new for this?
> > > >
> > > > No.
> > > >
> > > > Or more exactly, 200usec is my calculation mistake. your program call
> > > > mlock
> > > > 3 times per each iteration. so, correct cost is 66usec.
> > > yes, so mlock can do 15000/s, it is even slower than the whole i/o time
> > > for some not very fast ssd disk and I don't think it is endurable. I
> > > guess we should remove it, right? Or you have another other suggestion
> > > that I can try for it?
> >
> > read whole thread.
> I have read the whole thread, and you just described that the test case
> is artificial and there is no suggestion or patch about how to resolve
> it. As I have said that it is very time-consuming and with more cpu
> cores, the more penalty, and an i/o time for a ssd can be faster than
> it. So do you think 66 usec is OK for a memory operation?

I don't think you've read the thread at all. please read akpm's commnet.

http://www.spinics.net/lists/linux-mm/msg28290.html




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