Re: [PATCH v2] mm/dmapool.c: avoid duplicate memset within dma_pool_alloc

[Liu Song]

A helper function "use_dev_coherent_memory" is introduced here to

> > > > determine whether the memory is allocated by "dma_alloc_from_dev_coherent".
> > > >
> > > > And use "get_dma_ops" to determine whether the memory is allocated by
> > > > "dma_direct_alloc".
> WTF?  get_dma_ops is privat to the DMA API layer, and dmapool has no
> business even using that.  Even independent of this particular case,
> consumers of an API never have any business looking at the implementation
> of the API, that is the whole point of the abstraction.
>
> > It's not even that, the change here is just obviously broken, since it ends
> > up entirely ignoring want_init_on_alloc() for devices using dma-direct.
> > Sure, the memory backing a dma_page is zeroed *once* by its initial
> > dma-coherent allocation, but who says we're not not reallocating pool
> > entries from an existing dma_page?
> And yes, in addition to that it also is completely broken.

After reading everyone's comments, I found that fixing this patch will

make the code look strange, so the benefits of the changes will be

dispensable, so I also agree to discard this patch.

Sorry for this trouble again.


Thanks