My current test focuses on the looping case, where I repeatedly
scan a file whose size is larger than the memory size but less
than two times of memory sizes. My initial results are as follows:
My machine has 2GB memory.
The size of the file to be scanned is 2.5GB.
I looped for 4 time. The times and associated disk bandwidths
for each loop are below:
loop 0 time = 34.229424s bandwith = 76.58MB
loop 1 time = 37.574041s bandwith = 69.76MB
loop 2 time = 38.181791s bandwith = 68.65MB
loop 3 time = 38.141794s bandwith = 68.72MB
This shows that the current patches cannot do a
better job than the original kernel, which notoriously
underperforms for the case -- no matter how many times
the file is accessed, no hits at all. Meanwhile, Clock-Pro
is supposed to do a better job, because part of the
file can be protected in the active list and get a decent
number of hits.
Here is from /proc/meminfo:
Active: 11356 kB
Inactive: 1994400 kB
So no file pages are promoted into the active list, just
as in the original kernel.
Here is from /proc/refaults:
Refault distance Hits
0 - 32768 192
32768 - 65536 269
65536 - 98304 447
98304 - 131072 603
131072 - 163840 1087
163840 - 196608 909
196608 - 229376 558
229376 - 262144 404
262144 - 294912 287
294912 - 327680 191
327680 - 360448 79
360448 - 393216 68
393216 - 425984 41
425984 - 458752 45
458752 - 491520 31
New/Beyond 491520 2443
In the statistic, we do see many hits at the distance of around
150,000 pages. If we consider the inactive list size (1.9GB),
this position corresponds to the file size. However, if everything
happens as expected, all the hits should happen at the
distance. Unfortunately, there are also many hits listed as
New/Beyond. Because "Beyond"s should not be there, are they all
"New"s? Futhermore, I didn't see where the refault_histogram
statistics get reset, though they almost stop increasing after
the first run. Can you show me that?
Song Jiang
at LANL
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