Re: [PATCH] mm: do not drain pagevecs for mlock
From: KOSAKI Motohiro
Date: Fri Jan 06 2012 - 01:33:08 EST
(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.
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