Re: strange i/o faults.....

From: Jonathan Larmour <>
Date: Thu, 28 Nov 1996 23:50:16 GMT

At 21:12 28/11/96 +0100, Michael Boettger wrote:
>> From: James R Grinter <>
>> On Thu 28 Nov, 1996, "Michael Boettger" <> wrote:
>> > Is it normal to get that much physikal i/o page faults ????
>> > Page faults with physical i/o: 28122
>Thanx for the quick answer but that canīt be true. Here is my "cat

I think you'll find that 28122*PAGE_SIZE i.e. 28122*4096 = 115Mb, then add a
few Mb of shared libraries (from ps -axu), will not be too dissimilar from
the total size of Squid (from ps -axu or mallinfo() (NOT necessarily what
squid declares as its usage)). There will be a little difference but not much.

The reason is that while Linux may allocate you the space in principle when
you malloc, it does not actually give you real pages in memory (whether
immediately available or not). It instead relies on page faulting do this.
This is because malloc() calls brk() which calls into the kernel as
sys_brk() which calls do_mmap() i.e. it is the same process as mmap.

I would imagine the same holds for most half-decent modern OS's.

Jonathan L.
Origin IT Services Ltd., 323 Cambridge Science Park, Cambridge, England.
Tel: +44 (1223) 423355 Fax: +44 (1223) 420724 E-mail: guess...
-------[ Do not think that every sad-eyed woman has loved and lost... ]------
-----------------------[ she may have got him. -Anon ]-----------------------
These opinions are all my own fault.
Received on Thu Nov 28 1996 - 15:54:17 MST

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