2011-06-30

alloc'order and size

6.2: adda/mem'mgt/alloc'order and size:
. when using the c lang's dynamic mem'allocator (malloc)
the c`runtime assumes you will be
returning mem in mostly the same order as
when you obtained them .
. if this is not the case,
then there could be heap fragmentation problems .
[6.3:
. use of malloc order may be less complicated
because in modern systems there is v.mem,
so the parts of heap that are
in the way of compacting it
can simply be paged out .]

. the less mem you use at any one time,
the better chance buggy programs around you
don't blow up from exceeding mem limits .

. if needing to alloc mem in a way that could
cause heap fragmentation,
consider how much mem your program is using at once,
and whether you can break it into pieces
that do inout on temp files .

6.17: other strategies:
# at the app level:
. it's easier to find mem even in a fragmented heap
if you're decomposing your mem needs into smaller parts;
eg, instead of alloc'ing 100 contiguous words
for a 10x10 matrix,
you could do 10 alloc's of 10 words each
arranged as an array of pointer to arrays .
# at the os level:
. just as logical files are strings of
many non-contiguous physical mem blocks;
malloc could be impl'ing large mem requests
as strings of smaller mem blocks .