Re: [PATCH] eal: allow swapping of malloc heaps

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 15 Sep 2023 13:27:03 +0100
Bruce Richardson <bruce.richardson@intel.com> wrote:

> The external memory functions in DPDK allow the addition of externally
> access memory to malloc heaps, but with one major restriction - the
> memory must be allocated to an application-created heap, not one of the
> standard DPDK heaps for a NUMA node.
> 
> This restriction makes it difficult - if not impossible - to use
> externally allocated memory for DPDK by default. However, even if the
> restriction is relaxed, so we can add external memory to e.g. the socket
> 0 heap, there would be no way to guarantee that the external memory
> would be used in preference to the standard DPDK hugepage memory for a
> given allocation.
> 
> To give appropriately defined behaviour, a better solution is to allow
> the application to explicitly swap a pair of heaps. With this one new
> API in place, it allows the user to configure a new malloc heap, add
> external memory to it, and then replace a standard socket heap with the
> newly created one - thereby guaranteeing future allocations from the
> external memory.
> 
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> ---

Should document any restrictions about when this can be done.
Doesn't look thread safe. Would expect that application would do this
just after EAL init before doing any work.

What happens to memory allocated from old heap.