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SubjectRe[2]: MMAP vs READ/WRITE
Hello Oleg,

Wednesday, March 13, 2002, 4:41:58 PM, you wrote:

OD> Hello!

OD> On Wed, Mar 13, 2002 at 04:17:18PM +0300, Peter Zaitsev wrote:
>> So I would say mmap is not really optimized nowdays in Linux and so
>> read() may be wining in cases it should not. May be read-ahead is
>> used with read and is not used with mmap.

OD> how about reading manual page on madvise(2) and redoing your test?

OK. I did but no luck. The results are quite the same.

I think the hugest problem is:

0 2 0 210736 19472 2000 733188 216 0 5068 2 382 340 4 2 94
0 2 0 210424 20108 1860 729596 219 0 4732 0 319 352 4 1 96
0 2 0 210216 19652 1616 727280 254 0 4718 10 313 298 3 4 93
1 1 0 209756 19988 1744 723940 285 0 4523 14 313 197 6 6 88
0 2 0 209700 20096 1904 722236 223 0 4485 15 307 265 7 5 88

So then file is memory mapped and is read from some pages are coming
out from swap instead of being read from file....


OD> Also cache is best cleaned by unmounting filesystem in question
OD> and then mounting it back.

Well. This was not really needed as I repeated the test several times
in a loop without clearing the cache after initial cleaning to see how
stable are results.




--
Best regards,
Peter mailto:pz@spylog.ru

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