On Fri, Nov 27, 2020 at 03:06:24PM +0200, Joonas Lahtinen wrote:
> Quoting [email protected] (2020-11-24 08:07:39)
> > From: Ira Weiny <[email protected]>
> >
> > Working through a conversion to a call such as kmap_thread() revealed
> > many places where the pattern kmap/memcpy/kunmap occurred.
> >
> > Eric Biggers, Matthew Wilcox, Christoph Hellwig, Dan Williams, and Al
> > Viro all suggested putting this code into helper functions. Al Viro
> > further pointed out that these functions already existed in the iov_iter
> > code.[1]
> >
> > Placing these functions in 'highmem.h' is suboptimal especially with the
> > changes being proposed in the functionality of kmap. From a caller
> > perspective including/using 'highmem.h' implies that the functions
> > defined in that header are only required when highmem is in use which is
> > increasingly not the case with modern processors. Some headers like
> > mm.h or string.h seem ok but don't really portray the functionality
> > well. 'pagemap.h', on the other hand, makes sense and is already
> > included in many of the places we want to convert.
> >
> > Another alternative would be to create a new header for the promoted
> > memcpy functions, but it masks the fact that these are designed to copy
> > to/from pages using the kernel direct mappings and complicates matters
> > with a new header.
> >
> > Lift memcpy_to_page(), memcpy_from_page(), and memzero_page() to
> > pagemap.h.
> >
> > Also, add a memcpy_page(), memmove_page, and memset_page() to cover more
> > kmap/mem*/kunmap. patterns.
> >
> > [1]
> > https://lore.kernel.org/lkml/[email protected]/
> > https://lore.kernel.org/lkml/[email protected]/
> >
> > Cc: Dave Hansen <[email protected]>
> > Suggested-by: Matthew Wilcox <[email protected]>
> > Suggested-by: Christoph Hellwig <[email protected]>
> > Suggested-by: Dan Williams <[email protected]>
> > Suggested-by: Al Viro <[email protected]>
> > Suggested-by: Eric Biggers <[email protected]>
> > Signed-off-by: Ira Weiny <[email protected]>
>
> <SNIP>
>
> > +static inline void memset_page(struct page *page, int val, size_t offset,
> > size_t len)
> > +{
> > + char *addr = kmap_atomic(page);
> > + memset(addr + offset, val, len);
> > + kunmap_atomic(addr);
> > +}
>
> Other functions have (page, offset) pair. Insertion of 'val' in the middle
> here required
> to take a double look during review.
Let's be explicit here. Your suggested order is:
(page, offset, val, len)
right? I think I would prefer that to (page, val, offset, len).
