8 Nov
2007
8 Nov
'07
10:13 p.m.
2007/11/9, David Olofson <david(a)olofson.net>et>:
Mmmm... in my opinion someone could contact the TLSF authors and see
what can be done.
However, I was thinking something like this: IIRC the TLSF allocator
uses a bitmap with chunks of different size, covering the whole pool,
which is built when the allocator is instantiated. Then, when you
request some piece of memory, it starts looking for it from the block
of minimum size which could be used, and then continues looking for
the next block available (which is by construction equal or bigger in
size then the first).
The address of the first block can be resolved with a O(1) algorithm.
I was thinking that when the memory is "near to saturation", the
allocator could malloc() a new pool whose size is equal to that of the
first pool (maybe using a background thread) so that the bitmap for
the new pool is actually the same. Now the address resolving algorithm
should know in some way that the first pool is full for blocks of that
size or bigger, so the adress should be resolved in the second pool,
and so on.
This is just a thought... I never really wrote or worked on an allocator :-)
Anyway, getting back to the initial question, I think that we should
have two separate extensions, one for RT fixed size allocators and one
for "real" RT-safe allocators.
Stefano
On Friday 09 November 2007, Stefano D'Angelo
wrote:
[...]
Yes, that's what it does - which is why I suggested it. ;-)
[...]
Well, not really; you could just wrap the memory manager, adding
a 'manager' field to every chunk. Then you can just throw in another
TLSF manager instance when you need more memory. The 'manager' field
will point the free() wrapper to the correct manager instance.
Argh!
Yes,
that's exactly my point, but I think it needs to deal with
arbitrary size chunks to actually be able to serve that purpose in
real applications.
IIRC the TLSF allocator can do that.
Wouldn't it be more useful with some interface that allows plugins
to request memory in a non-blocking manner, and if instant
allocation fails, have the host notify the plugin when the memory
is available?
Basically, a malloc() call that means "If I can't have this memory
right away, please expand the pool so I can have it later!"
Mmmm.. I guess it's not easy to resize the pool in a rt-safe way. However, a nice, clean, efficient solution might be a
bit harder to
come up with, I think. IIRC, the current TLSF implementations scale
various internal structures and stuff to fit the pool size, so you
can't just bump the "brk limit" later.
I remember this way too.
Maybe hack TLSF to take a "maximum address
span" init argument, so you
can extend the pool as needed up to that limit? You'd just allocate
new blocks with malloc() and instruct the hacked TLSF to extend to
the end of that block, while pre-allocating (throwing away) any holes
caused by unrelated malloc()s.
Maybe I just don't understand, but however doesn't this mean, in
practice, allocating all of the memory right from the start? In such
case, why should you do something like that?
And even if
you have some background thread doing it when it's
needed, I think it's very hard to do that while plugins are running,
and so allocating and modifying on that memory.
Yes, that's why you can't realloc() the pool. You really have to add
new blocks of memory to it.