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Date: Wed, 15 Jun 2022 11:35:09 +0200
From: David Hildenbrand <david@...hat.com>
To: Muchun Song <songmuchun@...edance.com>, corbet@....net,
akpm@...ux-foundation.org, paulmck@...nel.org,
mike.kravetz@...cle.com, osalvador@...e.de
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, duanxiongchun@...edance.com, smuchun@...il.com
Subject: Re: [PATCH v2 1/2] mm: memory_hotplug: enumerate all supported
section flags
On 20.05.22 04:55, Muchun Song wrote:
> We are almost running out of section flags, only one bit is available in
> the worst case (powerpc with 256k pages). However, there are still some
> free bits (in ->section_mem_map) on other architectures (e.g. x86_64 has
> 10 bits available, arm64 has 8 bits available with worst case of 64K
> pages). We have hard coded those numbers in code, it is inconvenient to
> use those bits on other architectures except powerpc. So transfer those
> section flags to enumeration to make it easy to add new section flags in
> the future. Also, move SECTION_TAINT_ZONE_DEVICE into the scope of
> CONFIG_ZONE_DEVICE to save a bit on non-zone-device case.
>
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
Sorry for the late reply. This looks overly complicated to me.
IOW, staring at that patch I don't quite like what I am seeing.
Something like the following is *a lot* easier to read than some
MAPPER macro magic. What speaks against it?
/*
* Section bits use the lower unused bits in the ->section_mem_map
*/
enum {
SECTION_MARKED_PRESENT_BIT = 0,
SECTION_HAS_MEM_MAP_BIT,
...
#ifdef ZONE_DEVICE
SECTION_TAINT_ZONE_DEVICE_BIT
#endif
}
#define SECTION_MARKED_PRESENT (1ULL << SECTION_MARKED_PRESENT_BIT)
...
#ifdef ZONE_DEVICE
#define SECTION_TAINT_ZONE_DEVICE (1ULL << SECTION_TAINT_ZONE_DEVICE_BIT)
#endif /* ZONE_DEVICE */
> ---
> include/linux/kconfig.h | 1 +
> include/linux/mmzone.h | 54 +++++++++++++++++++++++++++++++++++++++++--------
> mm/memory_hotplug.c | 6 ++++++
> 3 files changed, 53 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/kconfig.h b/include/linux/kconfig.h
> index 20d1079e92b4..7044032b9f42 100644
> --- a/include/linux/kconfig.h
> +++ b/include/linux/kconfig.h
> @@ -10,6 +10,7 @@
> #define __LITTLE_ENDIAN 1234
> #endif
>
> +#define __ARG_PLACEHOLDER_ 0,
> #define __ARG_PLACEHOLDER_1 0,
> #define __take_second_arg(__ignored, val, ...) val
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 299259cfe462..2cf2a76535ab 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1422,16 +1422,47 @@ extern size_t mem_section_usage_size(void);
> * (equal SECTION_SIZE_BITS - PAGE_SHIFT), and the
> * worst combination is powerpc with 256k pages,
> * which results in PFN_SECTION_SHIFT equal 6.
> - * To sum it up, at least 6 bits are available.
> + * To sum it up, at least 6 bits are available on all architectures.
> + * However, we can exceed 6 bits on some other architectures except
> + * powerpc (e.g. 15 bits are available on x86_64, 13 bits are available
> + * with the worst case of 64K pages on arm64) if we make sure the
> + * exceeded bit is not applicable to powerpc.
> */
> -#define SECTION_MARKED_PRESENT (1UL<<0)
> -#define SECTION_HAS_MEM_MAP (1UL<<1)
> -#define SECTION_IS_ONLINE (1UL<<2)
> -#define SECTION_IS_EARLY (1UL<<3)
> -#define SECTION_TAINT_ZONE_DEVICE (1UL<<4)
> -#define SECTION_MAP_LAST_BIT (1UL<<5)
> +#define ENUM_SECTION_FLAG(MAPPER) \
> + MAPPER(MARKED_PRESENT) \
> + MAPPER(HAS_MEM_MAP) \
> + MAPPER(IS_ONLINE) \
> + MAPPER(IS_EARLY) \
> + MAPPER(TAINT_ZONE_DEVICE, CONFIG_ZONE_DEVICE) \
> + MAPPER(MAP_LAST_BIT)
> +
> +#define __SECTION_SHIFT_FLAG_MAPPER_0(x)
> +#define __SECTION_SHIFT_FLAG_MAPPER_1(x) SECTION_##x##_SHIFT,
> +#define __SECTION_SHIFT_FLAG_MAPPER(x, ...) \
> + __PASTE(__SECTION_SHIFT_FLAG_MAPPER_, IS_ENABLED(__VA_ARGS__))(x)
> +
> +#define __SECTION_FLAG_MAPPER_0(x)
> +#define __SECTION_FLAG_MAPPER_1(x) SECTION_##x = BIT(SECTION_##x##_SHIFT),
> +#define __SECTION_FLAG_MAPPER(x, ...) \
> + __PASTE(__SECTION_FLAG_MAPPER_, IS_ENABLED(__VA_ARGS__))(x)
> +
> +enum {
> + /*
> + * Generate a series of enumeration flags like SECTION_$name_SHIFT.
> + * Each entry in ENUM_SECTION_FLAG() macro will be generated to one
> + * enumeration iff the 2nd parameter of MAPPER() is defined or absent.
> + * The $name comes from the 1st parameter of MAPPER() macro.
> + */
> + ENUM_SECTION_FLAG(__SECTION_SHIFT_FLAG_MAPPER)
> + /*
> + * Generate a series of enumeration flags like:
> + * SECTION_$name = BIT(SECTION_$name_SHIFT)
> + */
> + ENUM_SECTION_FLAG(__SECTION_FLAG_MAPPER)
> +};
> +
> #define SECTION_MAP_MASK (~(SECTION_MAP_LAST_BIT-1))
> -#define SECTION_NID_SHIFT 6
> +#define SECTION_NID_SHIFT SECTION_MAP_LAST_BIT_SHIFT
>
> static inline struct page *__section_mem_map_addr(struct mem_section *section)
> {
> @@ -1470,12 +1501,19 @@ static inline int online_section(struct mem_section *section)
> return (section && (section->section_mem_map & SECTION_IS_ONLINE));
> }
>
> +#ifdef CONFIG_ZONE_DEVICE
> static inline int online_device_section(struct mem_section *section)
> {
> unsigned long flags = SECTION_IS_ONLINE | SECTION_TAINT_ZONE_DEVICE;
>
> return section && ((section->section_mem_map & flags) == flags);
> }
> +#else
> +static inline int online_device_section(struct mem_section *section)
> +{
> + return 0;
> +}
> +#endif
>
> static inline int online_section_nr(unsigned long nr)
> {
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 1213d0c67a53..3b360eda933f 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -672,12 +672,18 @@ static void __meminit resize_pgdat_range(struct pglist_data *pgdat, unsigned lon
>
> }
>
> +#ifdef CONFIG_ZONE_DEVICE
> static void section_taint_zone_device(unsigned long pfn)
> {
> struct mem_section *ms = __pfn_to_section(pfn);
>
> ms->section_mem_map |= SECTION_TAINT_ZONE_DEVICE;
> }
> +#else
> +static inline void section_taint_zone_device(unsigned long pfn)
> +{
> +}
> +#endif
>
> /*
> * Associate the pfn range with the given zone, initializing the memmaps
--
Thanks,
David / dhildenb
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