Re: [Lhms-devel] [PATCH 0/7] Fragmentation Avoidance V19

[Jeff Dike]

On Wed, Nov 02, 2005 at 05:28:35PM -0600, Rob Landley wrote:
> With fragmentation reduction and prezeroing, UML suddenly gains the option of 
> calling madvise(DONT_NEED) on sufficiently large blocks as A) a fast way of 
> prezeroing, B) a way of giving memory back to the host OS when it's not in 
> use.

DONT_NEED is insufficient.  It doesn't discard the data in dirty
file-backed pages.

Badari Pulavarty has a test patch (google for madvise(MADV_REMOVE))
which does do the trick, and I have a UML patch which adds memory
hotplug.  This combination does free memory back to the host.

				Jeff
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