Peter:
It's been several years since I had a hand in that code (as the team
leader of the VSM development team for the first release of MVS back in
1972-1974), but someone mentioned the existence of the FQE (Free Queue
Element). The FQE described the number of bytes that were free within
the block of storage obtained. If the storage size requested was less
than a page or some multiple of pages, there would be some free space,
which would always be in the first page of the obtained area and an FQE
would be put at the start of that first page to identify the amount of
free space.
Storage requests were always oriented to the high end of of the last
page of the requested area, so that an attempt to access storage beyond
the end of the area would result in a page fault. The idea being that
the more common storage addressing error resulted from having a
legitimate storage address, but an offset that exceeded the size of the
actual obtained area.
Mike Myers
Mentor Services Corporation
On 12/02/2015 10:07 AM, Peter Hunkeler wrote:
Allocating 100 MB area, I found that the first page in the newly allocated area
always seems to be backed by real storage upon return from STORAGE OBTAIN.
Before or after actual reference?
I tought "upon return from STORAGE OBTAIN" would be clear. Anyway, no I have
not referenced any byte within the new area. I found by looking at the area in a dump.
--
Peter Hunkeler
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