On Sat 16-12-17 08:44:19, Matthew Wilcox wrote:
> From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
>
> I found the struct { union { struct { union { struct { } } } } }
> layout rather confusing. Fortunately, there is an easier way to write
> this. The innermost union is of four things which are the size of an
> int, so the ones which are used by slab/slob/slub can be pulled up
> two levels to be in the outermost union with 'counters'. That leaves
> us with struct { union { struct { atomic_t; atomic_t; } } } which
> has the same layout, but is easier to read.
This is where the pahole output would be really helpeful. The patch
looks OK, I will double check with a fresh brain tomorrow (with the rest
of the series), though.
> Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
> ---
> include/linux/mm_types.h | 40 +++++++++++++++++++---------------------
> 1 file changed, 19 insertions(+), 21 deletions(-)
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 4509f0cfaf39..27973166af28 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -84,28 +84,26 @@ struct page {
> */
> unsigned counters;
> #endif
> - struct {
> + unsigned int active; /* SLAB */
> + struct { /* SLUB */
> + unsigned inuse:16;
> + unsigned objects:15;
> + unsigned frozen:1;
> + };
> + int units; /* SLOB */
> +
> + struct { /* Page cache */
> + /*
> + * Count of ptes mapped in mms, to show when
> + * page is mapped & limit reverse map searches.
> + *
> + * Extra information about page type may be
> + * stored here for pages that are never mapped,
> + * in which case the value MUST BE <= -2.
> + * See page-flags.h for more details.
> + */
> + atomic_t _mapcount;
>
> - union {
> - /*
> - * Count of ptes mapped in mms, to show when
> - * page is mapped & limit reverse map searches.
> - *
> - * Extra information about page type may be
> - * stored here for pages that are never mapped,
> - * in which case the value MUST BE <= -2.
> - * See page-flags.h for more details.
> - */
> - atomic_t _mapcount;
> -
> - unsigned int active; /* SLAB */
> - struct { /* SLUB */
> - unsigned inuse:16;
> - unsigned objects:15;
> - unsigned frozen:1;
> - };
> - int units; /* SLOB */
> - };
> /*
> * Usage count, *USE WRAPPER FUNCTION* when manual
> * accounting. See page_ref.h
> --
> 2.15.1
>
> --
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--
Michal Hocko
SUSE Labs
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