SKEY TCODE FLNU (1'10') -- Nucleus chain. Set for both the low storage
and high storage nucleus chains.
FLPA (1'08') -- Page available. This flag is set if there is
a full 4K page available on the chain. This flag may be set
even if there is no such page available.
contains the one-byte storage key assigned to storage on this
chain.
contains the one-byte FREETAB table code for storage on this
chain. When DMSFREE with TYPE=USER (the default) is called, one or more of the
following steps are taken in an attempt to satisfy the request. As soon as one of following then frea allocation processing terminates.
1. Search the low storage user chain for a block of the required size.
2. Search the high storage user chain for a block of the required
size.
3. Extend high storage user storage downward into the user program
area, modifying FREELOVE in the process.
4. For a variable request, put all available storage in the user
program area onto the high storage user chain, and then allocate
the largest block available on either the high storage user chain
or the low storage user chain. The allocated block will not be
satisfactory unless it is larger than the minimum requested size. When DMSFREE with TYPE=NUCLEUS is called, the fcllowing steps are taken
in an attempt td satisfy the until one succeeds:
1. Search the low storage nucleus chain for a block of the required 2. Get free pages from the low storage user chain, if any are
available, and put them on the low storage nucleus chain.
3. Search the high storage nucleus chain for a block of the -required size.
4. Get free pages from the high storage user chain, if they are
available, and put them on the high storage nucleus chain.
5. Extend high storage nucleus storage downward into the User Program Area, modifying FREELOVE in the process.
6. For variable requests, put all available pages from the user chains
and the user program area onto the nucleus chains, and allocate the
largest block available on either the low storage nucleus chains,
or the high storage nucleus chains. 2-20 IBM VM/370 System Logic and Program Determination--Volume 2

The DMSFRET macro releases free storage previously allocated with the DMSFREE macro. The format of the DMSFRET macro is:
[label] DMSFRET I label DiORDS={ n } (0) LOC={laddr} (1) r ,
ERR=lladdrl 1*' L r , I I r r " r r " I I,ERR=lladdrl I II I I I * II I IBALRII I L L JJ L L JJ J is any valid Assembler language label.
is the number of doublewords of storage to be released. DWORDS=n specifies the number of doublewords directly and DWORDS=(O) indicates that register 0 contains the number of doublewords being released.
is the address
"laddr" is any
(load address)
address directly
in register 1.
of the block of storage being released.
address that can be referred to in an LA instruction. LOC=laddr specifies the
while LOC=(1) indicates the address is
is the return address if an error occurs. "laddr" is any
address that can be referred to ty an LA (load address)
instruction. The error return is taken if there is a macro coding error or if there is a problem returning the
storage. If an asterisk (*) is specified, the error
return address is the same as the normal return address.
There is no default for this operand. If it is oaitted and an error occurs, the system will abend. I indicates how control is passed to Since DMSFRET IBALRI is a nucleus-resident routine, otner nucleus-resident
L routines can branch directly to it while
routines that are not nucleus-resident must use SVC linkage (TYPCALL=SVC). When DMSFRET is called, the block being released is placed on the
appropriate chain. At that point, the final update operation is
performed, if necessary, to advance FREELOWE, or to move pages from the
nucleus chain to the corresponding user chain. Similar update operations will be performed, when necessary, after
calls to DMSFREE, as well. RELEASING ALLOCATED STORAGE Storage allocated by the GETMAIN macro instruction may be released in
any of the following ways:
1. A specific block of such storage may be released by means of the FREEMAIN macro instruction. CMS Introduction 2-21