Re: [PATCH] iommu/dma: Zero pages manually in a length of scatterlist

[Robin Murphy]

On 05/11/2018 14:58, Christoph Hellwig wrote:
> On Fri, Nov 02, 2018 at 04:36:13PM -0700, Nicolin Chen wrote:
> > > What if the pages came from highmem? I know that doesn't happen on arm64
> > > today, but the point of this code *is* to be generic, and other users will
> > > arrive eventually.
> >
> > Hmm, so it probably should use sg_miter_start/stop() too? Looking
> > at the flush routine doing in PAGE_SIZE for each iteration, would
> > be possible to map and memset contiguous pages together? Actually
> > the flush routine might be also optimized if we can map contiguous
> > pages.
>
> FYI, I have patches I plan to submit soon that gets rid of the
> struct scatterlist use in this code to simplify it:

...and I have some significant objections to that simplification which I 
plan to respond with ;)

(namely that it defaults the whole higher-order page allocation business 
which will have varying degrees of performance impact on certain cases)

Robin.