Re: [PATCH v1 3/6] mem: add dirty malloc element support

[Thomas Monjalon <thomas@monjalon.net>]

17/01/2022 09:07, Dmitry Kozlyuk:
> EAL malloc layer assumed all free elements content
> is filled with zeros ("clean"), as opposed to uninitialized ("dirty").
> This assumption was ensured in two ways:
> 1. EAL memalloc layer always returned clean memory.
> 2. Freed memory was cleared before returning into the heap.
> 
> Clearing the memory can be as slow as around 14 GiB/s.
> To save doing so, memalloc layer is allowed to return dirty memory.
> Such segments being marked with RTE_MEMSEG_FLAG_DIRTY.
> The allocator tracks elements that contain dirty memory
> using the new flag in the element header.
> When clean memory is requested via rte_zmalloc*()
> and the suitable element is dirty, it is cleared on allocation.
> When memory is deallocated, the freed element is joined
> with adjacent free elements, and the dirty flag is updated:
> 
>     dirty + freed + dirty = dirty  =>  no need to clean
>             freed + dirty = dirty      the freed memory

It is not said why dirty parts are not cleaned.

> 
>     clean + freed + clean = clean  =>  freed memory
>     clean + freed         = clean      must be cleared
>             freed + clean = clean
>             freed         = clean
> 
> As a result, memory is either cleared on free, as before,
> or it will be cleared on allocation if need be, but never twice.

It is not said whether it is a change for everybody,
or only when enabling an option.