[Xen-devel] [PATCH] [linux-2.6.18-xen] (take 2) transcendent memory ("tmem") linux-side changes

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

(take 2: incorporating Jan's comments)

Transcendent memory ("tmem") for Linux

Tmem, when called from a tmem-capable (paravirtualized) guest, makes
use of otherwise unutilized ("fallow") memory to create and manage
pools of pages that can be accessed from the guest either as
"ephemeral" pages or as "persistent" pages. In either case, the pages
are not directly addressible by the guest, only copied to and fro via
the tmem interface. Ephemeral pages are a nice place for a guest to
put recently evicted clean pages that it might need again; these pages
can be reclaimed synchronously by Xen for other guests or other uses.
Persistent pages are a nice place for a guest to put "swap" pages to
avoid sending them to disk. These pages retain data as long as the
guest lives, but count against the guest memory allocation.

This patch contains the Linux paravirtualization changes to
complement the tmem Xen patch (xen-unstable c/s 19646). It
implements "precache" (ext3 only as of now), "preswap",
and limited "shared precache" (ocfs2 only as of now) support.
CONFIG options are required to turn on
the support (but in this patch they default to "y").  If
the underlying Xen does not have tmem support or has it
turned off, this is sensed early to avoid nearly all
hypercalls.

Lots of useful prose about tmem can be found at
http://oss.oracle.com/projects/tmem 

Signed-off-by: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>

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