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SubjectRe: [PATCH 6/8] mm/highmem: make kmap cache coloring aware
On 07/22/2014 12:01 PM, Max Filippov wrote:
> From: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
>
> Provide hooks that allow architectures with aliasing cache to align
> mapping address of high pages according to their color. Such architectures
> may enforce similar coloring of low- and high-memory page mappings and
> reuse existing cache management functions to support highmem.
>
> Cc: linux-mm@kvack.org
> Cc: linux-arch@vger.kernel.org
> Cc: linux-mips@linux-mips.org
> Cc: David Rientjes <rientjes@google.com>
> Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
> [ Max: extract architecture-independent part of the original patch, clean
> up checkpatch and build warnings. ]
> Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
> ---
> Changes since the initial version:
> - define set_pkmap_color(pg, cl) as do { } while (0) instead of /* */;
> - rename is_no_more_pkmaps to no_more_pkmaps;
> - change 'if (count > 0)' to 'if (count)' to better match the original
> code behavior;
>
> mm/highmem.c | 19 ++++++++++++++++---
> 1 file changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/mm/highmem.c b/mm/highmem.c
> index b32b70c..88fb62e 100644
> --- a/mm/highmem.c
> +++ b/mm/highmem.c
> @@ -44,6 +44,14 @@ DEFINE_PER_CPU(int, __kmap_atomic_idx);
> */
> #ifdef CONFIG_HIGHMEM
>
> +#ifndef ARCH_PKMAP_COLORING
> +#define set_pkmap_color(pg, cl) do { } while (0)
> +#define get_last_pkmap_nr(p, cl) (p)
> +#define get_next_pkmap_nr(p, cl) (((p) + 1) & LAST_PKMAP_MASK)
> +#define no_more_pkmaps(p, cl) (!(p))
> +#define get_next_pkmap_counter(c, cl) ((c) - 1)
> +#endif
> +
> unsigned long totalhigh_pages __read_mostly;
> EXPORT_SYMBOL(totalhigh_pages);
>
> @@ -161,19 +169,24 @@ static inline unsigned long map_new_virtual(struct page *page)
> {
> unsigned long vaddr;
> int count;
> + int color __maybe_unused;
> +
> + set_pkmap_color(page, color);
> + last_pkmap_nr = get_last_pkmap_nr(last_pkmap_nr, color);
>
> start:
> count = LAST_PKMAP;
> /* Find an empty entry */
> for (;;) {
> - last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
> - if (!last_pkmap_nr) {
> + last_pkmap_nr = get_next_pkmap_nr(last_pkmap_nr, color);
> + if (no_more_pkmaps(last_pkmap_nr, color)) {
> flush_all_zero_pkmaps();
> count = LAST_PKMAP;
> }
> if (!pkmap_count[last_pkmap_nr])
> break; /* Found a usable entry */
> - if (--count)
> + count = get_next_pkmap_counter(count, color);
> + if (count)
> continue;
>
> /*
I would like to return back to "if (count >0)".

The reason is in easy way to jump through the same coloured pages - next
element is calculated via decrementing by non "1" value of colours and
it can easy become negative on last page available:

#define get_next_pkmap_counter(c,cl) (c - FIX_N_COLOURS)

where FIX_N_COLOURS is a max number of page colours.

Besides that it is a good practice in stopping cycle.

- Leonid.



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