Linux-kernel mailing list archive 1998-10,: Re: mmap() versus read()

# Re: mmap() versus read()

Albert D. Cahalan (acahalan@cs.uml.edu)
Sun, 8 Mar 1998 16:32:57 -0500 (EST)

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>> Why does Linux page executables from their original location?
>> Isn't that slower than putting it into the swapfile because
>> you have to wade through the filesystem layer when you need
>> to page in? Or is the penalty for writing it into the swap
>> bigger than the filesystem overhead?

Linux does not need as much swap that way. It is easy to run
Linux without any swap at all.

> Later versions of OS/2 have an attribute to specify that certain
> executables (DLLs that are of comparable usefulness to libc) get
> swapped out instead of having the code pages discarded and paged
> in from file. This apparently gives good performance gains.

Advanced filesystems like ext2 provide a way to mark an executable
so that the code pages won't get discarded: the sticky bit. :-)
It is an ancient feature actually, and it could be useful for libc.
I don't see any reason why it would have to be restricted to executables.

> I've seen reports stating that people were investigating the
> possibility of making certain file systems page code to the swap
> partition instead of discarding and paging in from the executable
> (for CD-ROM, NFS, and floppy).

That looks like a global sticky bit.

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