On Mon, Jun 20, 2022 at 09:51:42AM +0200, David Hildenbrand wrote:
> On 19.06.22 15:38, 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@xxxxxxxxxxxxx>
> > ---
> > include/linux/mmzone.h | 44 +++++++++++++++++++++++++++++++++++---------
> > mm/memory_hotplug.c | 6 ++++++
> > mm/sparse.c | 2 +-
> > 3 files changed, 42 insertions(+), 10 deletions(-)
> >
> > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> > index aab70355d64f..932843c6459b 100644
> > --- a/include/linux/mmzone.h
> > +++ b/include/linux/mmzone.h
> > @@ -1418,16 +1418,35 @@ 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 SECTION_MAP_MASK (~(SECTION_MAP_LAST_BIT-1))
> > -#define SECTION_NID_SHIFT 6
> > +enum {
> > + SECTION_MARKED_PRESENT_BIT,
> > + SECTION_HAS_MEM_MAP_BIT,
> > + SECTION_IS_ONLINE_BIT,
> > + SECTION_IS_EARLY_BIT,
> > +#ifdef CONFIG_ZONE_DEVICE
> > + SECTION_TAINT_ZONE_DEVICE_BIT,
> > +#endif
> > + SECTION_MAP_LAST_BIT,
> > +};
> > +
> > +enum {
> > + SECTION_MARKED_PRESENT = BIT(SECTION_MARKED_PRESENT_BIT),
> > + SECTION_HAS_MEM_MAP = BIT(SECTION_HAS_MEM_MAP_BIT),
> > + SECTION_IS_ONLINE = BIT(SECTION_IS_ONLINE_BIT),
> > + SECTION_IS_EARLY = BIT(SECTION_IS_EARLY_BIT),
> > +#ifdef CONFIG_ZONE_DEVICE
> > + SECTION_TAINT_ZONE_DEVICE = BIT(SECTION_TAINT_ZONE_DEVICE_BIT),
> > +#endif
> > +};
>
> I can understand the reason for the other enum, to auto-assing numbers.
> What's the underlying reason for the enum here? Personally, I'd just
> stay with defines, so I'm curious :)
>
Oh, just my personal preference. I can replace those with defines in
next version if you prefer it. :-)
Thanks.
> LGTM
>
> --
> Thanks,
>
> David / dhildenb
>
>
