[RFC v2 2/3] lib: add fastmem library

[Mattias Rönnblom]

On 5/26/26 15:23, Stephen Hemminger wrote:
> On Tue, 26 May 2026 10:57:42 +0200
> Mattias Rönnblom <hofors at lysator.liu.se> wrote:
> 
>> +__rte_experimental
>> +void *
>> +rte_fastmem_alloc(size_t size, size_t align, unsigned int flags)
>> +	__rte_alloc_size(1) __rte_alloc_align(2);
> 
> Should also add attribute __rte_malloc which tells compiler
> that pointer returned cannot alias other memory
> 
> And add __rte_dealloc(rte_fastmem_free, 1)
> which tells compiler that the returned pointer should only go
> back to fastmem (not free, rte_free, etc).

Done. Only works for the single-object ops (not bulk) though.

I've had a look at how to extend fastmem to support larger allocations 
(without suggesting this is the way to go).

Seems to me that implementation should be something like
a) slab allocator for small objects.
b) a cache-less per-socket page run allocator for mid-sized objects.
c) per-object memzones for large objects.

If one would implement that, you would essentially have a plug-in 
replacement for rte_malloc.h (maybe minus some debug and some more 
esoteric DPDK heap features).

Should fastmem be an outright replacement, or something that at least 
initially lives alongside the regular heap, maybe with a run- or 
compile-time option to make rte_malloc.h functions delegate to fastmem? 
This is unclear to me at this point. I fear the more ambitious, cleaner 
and more risky DPDK heap replacement path will go they way my attempts 
to replace rte_memcpy or rte_timer went.

I would agree with anyone saying that we should have only one heap-like 
API for memory allocations. rte_malloc.h obviously needs to stay, for 
backward compatibility reason, if nothing else. I would like to add bulk 
alloc/free, and allow for smaller alignments than 64, since slabs can do 
that efficiently (DPDK heap per-object header is 128 bytes!). One could 
either go about that by extending rte_malloc.h or deprecating that API 
and starting anew. In the latter case, one could do many more minor 
tweaks, like removing the type pointers (only a nuance), remove the 
validate function, change and extend the stats interface, etc.