Re: [PATCH v9 3/8] block: add check when merging zone device pages

John Hubbard
2022-09-05T23:58:39Z

On 8/25/22 08:24, Logan Gunthorpe wrote:
> Consecutive zone device pages should not be merged into the same sgl
> or bvec segment with other types of pages or if they belong to different
> pgmaps. Otherwise getting the pgmap of a given segment is not possible
> without scanning the entire segment. This helper returns true either if
> both pages are not zone device pages or both pages are zone device
> pages with the same pgmap.
>
> Add a helper to determine if zone device pages are mergeable and use
> this helper in page_is_mergeable().
>
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
> ---
> block/bio.c | 2 ++
> include/linux/mmzone.h | 24 ++++++++++++++++++++++++
> 2 files changed, 26 insertions(+)
>
> diff --git a/block/bio.c b/block/bio.c
> index 3d3a2678fea2..969607bc1f4d 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -865,6 +865,8 @@ static inline bool page_is_mergeable(const struct bio_vec *bv,
> return false;
> if (xen_domain() && !xen_biovec_phys_mergeable(bv, page))
> return false;
> + if (!zone_device_pages_have_same_pgmap(bv->bv_page, page))
> + return false;
>
> *same_page = ((vec_end_addr & PAGE_MASK) == page_addr);
> if (*same_page)
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index e24b40c52468..2c31915b057e 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -794,6 +794,25 @@ static inline bool is_zone_device_page(const struct page *page)
> {
> return page_zonenum(page) == ZONE_DEVICE;
> }
> +
> +/*
> + * Consecutive zone device pages should not be merged into the same sgl
> + * or bvec segment with other types of pages or if they belong to different
> + * pgmaps. Otherwise getting the pgmap of a given segment is not possible
> + * without scanning the entire segment. This helper returns true either if
> + * both pages are not zone device pages or both pages are zone device pages
> + * with the same pgmap.
> + */

Nice work on the documentation here. Approach looks correct.

Reviewed-by: John Hubbard <jhubbard@nvidia.com>

thanks,

--
John Hubbard
NVIDIA

> +static inline bool zone_device_pages_have_same_pgmap(const struct page *a,
> + const struct page *b)
> +{
> + if (is_zone_device_page(a) != is_zone_device_page(b))
> + return false;
> + if (!is_zone_device_page(a))
> + return true;
> + return a->pgmap == b->pgmap;
> +}
> +
> extern void memmap_init_zone_device(struct zone *, unsigned long,
> unsigned long, struct dev_pagemap *);
> #else
> @@ -801,6 +820,11 @@ static inline bool is_zone_device_page(const struct page *page)
> {
> return false;
> }
> +static inline bool zone_device_pages_have_same_pgmap(const struct page *a,
> + const struct page *b)
> +{
> + return true;
> +}
> #endif
>
> static inline bool folio_is_zone_device(const struct folio *folio)