On 05.04.2012 19:54, Alan Cox wrote:
On 04/04/2012 02:17, Konstantin Belousov wrote:
On Tue, Apr 03, 2012 at 11:02:53PM +0400, Andrey Zonov wrote:
[snip]
This is what I expect. But why this doesn't work without reading file
manually?
Issue seems to be in some change of the behaviour of the reserv or
phys allocator. I Cc:ed Alan.
I'm pretty sure that the behavior here hasn't significantly changed in
about twelve years. Otherwise, I agree with your analysis.
On more than one occasion, I've been tempted to change:
pmap_remove_all(mt);
if (mt->dirty != 0)
vm_page_deactivate(mt);
else
vm_page_cache(mt);
to:
vm_page_dontneed(mt);
Thanks Alan! Now it works as I expect!
But I have more questions to you and kib@. They are in my test below.
So, prepare file as earlier, and take information about memory usage
from top(1). After preparation, but before test:
Mem: 80M Active, 55M Inact, 721M Wired, 215M Buf, 46G Free
First run:
$ ./mmap /mnt/random
mmap: 1 pass took: 7.462865 (none: 0; res: 262144; super:
0; other: 0)
No super pages after first run, why?..
Mem: 79M Active, 1079M Inact, 722M Wired, 216M Buf, 45G Free
Now the file is in inactive memory, that's good.
Second run:
$ ./mmap /mnt/random
mmap: 1 pass took: 0.004191 (none: 0; res: 262144; super:
511; other: 0)
All super pages are here, nice.
Mem: 1103M Active, 55M Inact, 722M Wired, 216M Buf, 45G Free
Wow, all inactive pages moved to active and sit there even after process
was terminated, that's not good, what do you think?
Read the file:
$ cat /mnt/random > /dev/null
Mem: 79M Active, 55M Inact, 1746M Wired, 1240M Buf, 45G Free
Now the file is in wired memory. I do not understand why so.
Could you please give me explanation about active/inactive/wired memory?
because I suspect that the current code does more harm than good. In
theory, it saves activations of the page daemon. However, more often
than not, I suspect that we are spending more on page reactivations than
we are saving on page daemon activations. The sequential access
detection heuristic is just too easily triggered. For example, I've seen
it triggered by demand paging of the gcc text segment. Also, I think
that pmap_remove_all() and especially vm_page_cache() are too severe for
a detection heuristic that is so easily triggered.
[snip]
--
Andrey Zonov
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