Re: [PATCH RESEND v2 3/5] mm_zone: add function to check if managed dma zone exists

John Donnelly
2021-12-07T03:54:48Z

On 12/6/21 9:07 PM, Baoquan He wrote:
> In some places of the current kernel, it assumes that dma zone must have
> managed pages if CONFIG_ZONE_DMA is enabled. While this is not always true.
> E.g in kdump kernel of x86_64, only low 1M is presented and locked down
> at very early stage of boot, so that there's no managed pages at all in
> DMA zone. This exception will always cause page allocation failure if page
> is requested from DMA zone.
>
> Here add function has_managed_dma() and the relevant helper functions to
> check if there's DMA zone with managed pages. It will be used in later
> patches.
>
> Signed-off-by: Baoquan He <bhe@redhat.com>
Reviewed-by: John Donnelly <john.p.donnelly@oracle.com>
Tested-by: John Donnelly <john.p.donnelly@oracle.com>
> ---
> include/linux/mmzone.h | 21 +++++++++++++++++++++
> mm/page_alloc.c | 11 +++++++++++
> 2 files changed, 32 insertions(+)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 58e744b78c2c..82d23e13e0e5 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -998,6 +998,18 @@ static inline bool zone_is_zone_device(struct zone *zone)
> }
> #endif
>
> +#ifdef CONFIG_ZONE_DMA
> +static inline bool zone_is_dma(struct zone *zone)
> +{
> + return zone_idx(zone) == ZONE_DMA;
> +}
> +#else
> +static inline bool zone_is_dma(struct zone *zone)
> +{
> + return false;
> +}
> +#endif
> +
> /*
> * Returns true if a zone has pages managed by the buddy allocator.
> * All the reclaim decisions have to use this function rather than
> @@ -1046,6 +1058,7 @@ static inline int is_highmem_idx(enum zone_type idx)
> #endif
> }
>
> +bool has_managed_dma(void);
> /**
> * is_highmem - helper function to quickly check if a struct zone is a
> * highmem zone or not. This is an attempt to keep references
> @@ -1131,6 +1144,14 @@ extern struct zone *next_zone(struct zone *zone);
> ; /* do nothing */ \
> else
>
> +#define for_each_managed_zone(zone) \
> + for (zone = (first_online_pgdat())->node_zones; \
> + zone; \
> + zone = next_zone(zone)) \
> + if (!managed_zone(zone)) \
> + ; /* do nothing */ \
> + else
> +
> static inline struct zone *zonelist_zone(struct zoneref *zoneref)
> {
> return zoneref->zone;
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c5952749ad40..ac0ea42a4e5f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -9459,4 +9459,15 @@ bool take_page_off_buddy(struct page *page)
> spin_unlock_irqrestore(&zone->lock, flags);
> return ret;
> }
> +
> +bool has_managed_dma(void)
> +{
> + struct zone *zone;
> +
> + for_each_managed_zone(zone) {
> + if (zone_is_dma(zone))
> + return true;
> + }
> + return false;
> +}
> #endif
>