2. PERFORMANCE REPORTING ANALYSIS › 2.3 Auxiliary Storage Management Analysis › 2.3.4 MVS Concepts › 2.3.4.3 Swapping › 2.3.4.3.1 Physical Swap Algorithm

2.3.4.3.1 Physical Swap Algorithm

Ignoring the quiesce/restore and trimming steps, the swap
process of the extended swap IUP and MVS/SP 1.3 and beyond is
really a two-stage swap-out and a single-stage swap-in.

Changed but unreferenced pages are paged-out to local
data sets, saving the ASM slot locations in LSQA control
blocks.  MVS/XA and MVS/ESA use the sequential slot
allocation algorithm to select slots on the local page data
sets.

Then LSQA and non-LSQA referenced pages are paged-out to swap
data sets.  All the pages needed for a swap-in receive the
advantage of the sequential slots of swap sets.

If multiple swap sets are required for the larger working
sets, they will be split among multiple swap data sets and
the I/O will run concurrently (assuming a sufficient number
of allocated data sets).  When an address space is swapped
back into real memory, all of its pages are brought in from
the swap data sets in a single stage operation.