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

On 01/10/2012 07:58 AM, KOSAKI Motohiro wrote:

(1/6/12 1:46 AM), Tao Ma wrote:

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On 01/06/2012 02:33 PM, KOSAKI Motohiro wrote:

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(1/6/12 1:30 AM), Tao Ma wrote:

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On 01/06/2012 02:18 PM, KOSAKI Motohiro wrote:

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2012/1/6 Tao Ma[off-list ref]:

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Hi Kosaki,
On 12/30/2011 06:07 PM, KOSAKI Motohiro wrote:

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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

Oh, your patch set doesn't cc to me, so my mail filter moved it to
another directory..
Sorry and I will read the whole thread. Thanks again for your time.

Thanks
Tao

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