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SubjectRe: [PATCH 1/7] ubi: block: Refactor sg list processing for highmem
On Fri, Aug 11, 2023 at 10:34:52AM +0200, Richard Weinberger wrote:
> ----- Ursprüngliche Mail -----
> > Von: "Christoph Hellwig" <hch@infradead.org>
> > On Thu, Aug 10, 2023 at 09:54:46PM +0200, Richard Weinberger wrote:
> >> > But why add the bounce buffering first if you can avoid it from the
> >> > very beginning by just using kmap_local instead of adding a new
> >> > caller for the deprecate kmap_atomic?
> >>
> >> Because I want this fix also in all stable trees. kmap_local() is rather
> >> new. When back porting patch 1/7, bounce buffers and kmap_atomic()
> >> are needed anyway.
> >> By doing this in patch 1/7 I avoid backport troubles and keep the
> >> delta between upstream and stable trees minimal.
> >
> > Just use plain kmap for the historic backports.
>
> Hm, yes. For UBIblock kmap should be too expensive.

? kmap is a no-op for !highmem. And it will always be way cheaper
than bounce buffering for the case where you are actually fed highmem
pages.

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