Re: [PATCH 1/7] mm/page_alloc: Rename ALLOC_HIGH to ALLOC_MIN_RESERVE

Michal Hocko
2023-01-11T15:19:30Z

On Mon 09-01-23 15:16:25, Mel Gorman wrote:
> __GFP_HIGH aliases to ALLOC_HIGH but the name does not really hint
> what it means. As ALLOC_HIGH is internal to the allocator, rename
> it to ALLOC_MIN_RESERVE to document that the min reserves can
> be depleted.
>
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>

Naming is hard but ALLOC_HIGH is definitely much more confusing as it
can collide with high watermark. ALLOC_MIN_RESERVE says that some
reserves are involved. ALl the reserves are below min watermark by
defition but I cannot really come up with a better name. I do not think
we want to encode the amount of reserves into the name.

Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!
> ---
> mm/internal.h | 4 +++-
> mm/page_alloc.c | 8 ++++----
> 2 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/mm/internal.h b/mm/internal.h
> index bcf75a8b032d..403e4386626d 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -736,7 +736,9 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
> #endif
>
> #define ALLOC_HARDER 0x10 /* try to alloc harder */
> -#define ALLOC_HIGH 0x20 /* __GFP_HIGH set */
> +#define ALLOC_MIN_RESERVE 0x20 /* __GFP_HIGH set. Allow access to 50%
> + * of the min watermark.
> + */
> #define ALLOC_CPUSET 0x40 /* check for correct cpuset */
> #define ALLOC_CMA 0x80 /* allow allocations from CMA areas */
> #ifdef CONFIG_ZONE_DMA32
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 0745aedebb37..244c1e675dc8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3976,7 +3976,7 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
> /* free_pages may go negative - that's OK */
> free_pages -= __zone_watermark_unusable_free(z, order, alloc_flags);
>
> - if (alloc_flags & ALLOC_HIGH)
> + if (alloc_flags & ALLOC_MIN_RESERVE)
> min -= min / 2;
>
> if (unlikely(alloc_harder)) {
> @@ -4818,18 +4818,18 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
> unsigned int alloc_flags = ALLOC_WMARK_MIN | ALLOC_CPUSET;
>
> /*
> - * __GFP_HIGH is assumed to be the same as ALLOC_HIGH
> + * __GFP_HIGH is assumed to be the same as ALLOC_MIN_RESERVE
> * and __GFP_KSWAPD_RECLAIM is assumed to be the same as ALLOC_KSWAPD
> * to save two branches.
> */
> - BUILD_BUG_ON(__GFP_HIGH != (__force gfp_t) ALLOC_HIGH);
> + BUILD_BUG_ON(__GFP_HIGH != (__force gfp_t) ALLOC_MIN_RESERVE);
> BUILD_BUG_ON(__GFP_KSWAPD_RECLAIM != (__force gfp_t) ALLOC_KSWAPD);
>
> /*
> * The caller may dip into page reserves a bit more if the caller
> * cannot run direct reclaim, or if the caller has realtime scheduling
> * policy or is asking for __GFP_HIGH memory. GFP_ATOMIC requests will
> - * set both ALLOC_HARDER (__GFP_ATOMIC) and ALLOC_HIGH (__GFP_HIGH).
> + * set both ALLOC_HARDER (__GFP_ATOMIC) and ALLOC_MIN_RESERVE(__GFP_HIGH).
> */
> alloc_flags |= (__force int)
> (gfp_mask & (__GFP_HIGH | __GFP_KSWAPD_RECLAIM));
> --
> 2.35.3

--
Michal Hocko
SUSE Labs