Dale Ghent wrote:
I'm observing the segmap_kpm variable on a running 64bit kernel and
it's value is 0. It seems to be explicitly set as such at:
http://src.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/i86pc/os/startup.c#1969
The segmap segment cannot use KPM mappings on x64 systems
(x86 64bit systems) due to the PAGESIZE, MAXBSIZE mismatch,
hence segmap_kpm = 0.
...which overrides the apparent and perhaps desirable default defined at:
http://src.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/vm/seg_kpm.c#100
Does this mean that the segmap is not using the new KPM subsystem on
x86? Would it be correct to assume that the traditional segmap knob,
segmapsize, still applies? I'm
Yes segmap does not use KPM, but segmap segment still exists.
The knob still apply. The default segmap size on x64 system is 64MB.
The size of segmap segment can be tweaked by changing segmapsize
value.
trying to figure out the impact this has on systems that are large
NFSv3 clients.
However, a new set of interfaces called VPM was introduced
which provide transient mappings to file pages similar, to segmap. The
VPM interfaces use KPM mappings. The UFS, NFS, TMPFS and
SPECfs filesystem use the VPM interface where available.
Segmap is still available and is in limited use, there should be no need
to tweak the segmap size when VPM is available.
So, if you are concerned about the excessive cross calls issues
associated with the traditional segmap mappings, that has been
addressed by the VPM interfaces.
The VPM interface is also available for x64 systems on S10
starting update 6(I believe).
-Prakash.
Thanks for any insight
/dale
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