Understanding memhog

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From: tom@ancilla.toronto.on.ca (Tom Kelly)
Subject: Re: memhog/u386mon/ps  Why the differences?
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In article <3777A0B0.C186DF4F@caldera.com>,
 "James R. Sullivan" <jim@caldera.com> writes:
|> 
|> 
|> Ken Wolff wrote:
|> > 
|> > Running OSR505 I can look at a specific process using memhog (from
|> > Skunk98), u386mon 2.74 and ps and each gives me a different memory size.
|> > 
|> > memhog shows 1228
|> 
|> If I remember correctly, memhog shows the memory pages, which are 4K
|> in size.  Memhog also takes into account any shared libraries/text
|> that the process uses and spreads those shared pages across the
|> various processes that use the shared memory.  For instance, if you
|> had two processes that both used a shared library that used 10 pages
|> of memory, both process would be allocated 5 pages.

The sizes reported by memhog are in system pages (4K).  The vsize
column is the size (in pages) of the virtual address space for the
process.  All the other columns are real memory pages.

shrd is the total number of real pages in shareable memory regions
attached to this process.  priv shows the total number of real pages
in private memory regions attached to this process.  wtd attempts to
account for the actual sharing of shareable regions.  As Jim says,
the memory in a shared region is allocated equally among all the
sharing processes; this is the value in wtd.

Total is the sum of wtd and priv, and is intended to measure the process'
impact on the system's real memory.

Having said all that, just looking at a memhog running on my system
the wtd and shared columns are always the same, which suggests to me
that a bug has crept in.  (Or that my memory has completely 

|> 
|> I don't know about u386mon, but the man page for ps(C) is pretty clear
|> about the output for ps -l:
|> 
|> SZ
|> THe swappable size (in kilobytes) of the virtual data and stack segments

I wrote memhog partly because ps gives only virtual memory, not real, and I
wanted to look at real memory use.

Tom Kelly
tom@ancilla.toronto.on.ca

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