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Date: 2 Aug 2016 17:36:49 -0000
From: "John Levine" <>
Subject: Re: application frequently map and unmap memory

In article <> you write:
>I am looking for real-world applications
>I guess if some applications use large chunk of memory, map and unmap
>are necessary.
>I just am not aware which applications have such requirements.

If you just want to use a large chunk of memory, malloc() and free()
work fine.  Memory mapping is for situtations where you need to share
data between applications, or you want to do something on a whole file
so it's more efficicient to map the file into memory than to use reads
and writes.

My version of grepcidr uses mmap so it can scan through whole files as
fast as possible.  It's like the usual grep utility but specialized to
look for IP addresses, typically in large log files.

It uses a state machine to scan through each file which never backs up
by more than one character so its usage is map a file, scan through
the whole thing sequentially, unmap it, map in the next file, and so


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