Re: [PATCH v6 03/12] mm/sparsemem: Add helpers track active portions of a section at boot

[Pavel Tatashin <pasha.tatashin@soleen.com>]

[-- Attachment #1: Type: text/plain, Size: 8535 bytes --]

On Sat, May 4, 2019, 3:26 PM Dan Williams <dan.j.williams@intel.com> wrote:

> On Thu, May 2, 2019 at 9:12 AM Pavel Tatashin <pasha.tatashin@soleen.com>
> wrote:
> >
> > On Wed, Apr 17, 2019 at 2:53 PM Dan Williams <dan.j.williams@intel.com>
> wrote:
> > >
> > > Prepare for hot{plug,remove} of sub-ranges of a section by tracking a
> > > section active bitmask, each bit representing 2MB (SECTION_SIZE (128M)
> /
> > > map_active bitmask length (64)). If it turns out that 2MB is too large
> > > of an active tracking granularity it is trivial to increase the size of
> > > the map_active bitmap.
> >
> > Please mention that 2M on Intel, and 16M on Arm64.
> >
> > >
> > > The implications of a partially populated section is that pfn_valid()
> > > needs to go beyond a valid_section() check and read the sub-section
> > > active ranges from the bitmask.
> > >
> > > Cc: Michal Hocko <mhocko@suse.com>
> > > Cc: Vlastimil Babka <vbabka@suse.cz>
> > > Cc: Logan Gunthorpe <logang@deltatee.com>
> > > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> > > ---
> > >  include/linux/mmzone.h |   29 ++++++++++++++++++++++++++++-
> > >  mm/page_alloc.c        |    4 +++-
> > >  mm/sparse.c            |   48
> ++++++++++++++++++++++++++++++++++++++++++++++++
> > >  3 files changed, 79 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> > > index 6726fc175b51..cffde898e345 100644
> > > --- a/include/linux/mmzone.h
> > > +++ b/include/linux/mmzone.h
> > > @@ -1175,6 +1175,8 @@ struct mem_section_usage {
> > >         unsigned long pageblock_flags[0];
> > >  };
> > >
> > > +void section_active_init(unsigned long pfn, unsigned long nr_pages);
> > > +
> > >  struct page;
> > >  struct page_ext;
> > >  struct mem_section {
> > > @@ -1312,12 +1314,36 @@ static inline struct mem_section
> *__pfn_to_section(unsigned long pfn)
> > >
> > >  extern int __highest_present_section_nr;
> > >
> > > +static inline int section_active_index(phys_addr_t phys)
> > > +{
> > > +       return (phys & ~(PA_SECTION_MASK)) / SECTION_ACTIVE_SIZE;
> >
> > How about also defining SECTION_ACTIVE_SHIFT like this:
> >
> > /* BITS_PER_LONG = 2^6 */
> > #define BITS_PER_LONG_SHIFT 6
> > #define SECTION_ACTIVE_SHIFT (SECTION_SIZE_BITS - BITS_PER_LONG_SHIFT)
> > #define SECTION_ACTIVE_SIZE (1 << SECTION_ACTIVE_SHIFT)
> >
> > The return above would become:
> > return (phys & ~(PA_SECTION_MASK)) >> SECTION_ACTIVE_SHIFT;
> >
> > > +}
> > > +
> > > +#ifdef CONFIG_SPARSEMEM_VMEMMAP
> > > +static inline int pfn_section_valid(struct mem_section *ms, unsigned
> long pfn)
> > > +{
> > > +       int idx = section_active_index(PFN_PHYS(pfn));
> > > +
> > > +       return !!(ms->usage->map_active & (1UL << idx));
> > > +}
> > > +#else
> > > +static inline int pfn_section_valid(struct mem_section *ms, unsigned
> long pfn)
> > > +{
> > > +       return 1;
> > > +}
> > > +#endif
> > > +
> > >  #ifndef CONFIG_HAVE_ARCH_PFN_VALID
> > >  static inline int pfn_valid(unsigned long pfn)
> > >  {
> > > +       struct mem_section *ms;
> > > +
> > >         if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
> > >                 return 0;
> > > -       return valid_section(__nr_to_section(pfn_to_section_nr(pfn)));
> > > +       ms = __nr_to_section(pfn_to_section_nr(pfn));
> > > +       if (!valid_section(ms))
> > > +               return 0;
> > > +       return pfn_section_valid(ms, pfn);
> > >  }
> > >  #endif
> > >
> > > @@ -1349,6 +1375,7 @@ void sparse_init(void);
> > >  #define sparse_init()  do {} while (0)
> > >  #define sparse_index_init(_sec, _nid)  do {} while (0)
> > >  #define pfn_present pfn_valid
> > > +#define section_active_init(_pfn, _nr_pages) do {} while (0)
> > >  #endif /* CONFIG_SPARSEMEM */
> > >
> > >  /*
> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > index f671401a7c0b..c9ad28a78018 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -7273,10 +7273,12 @@ void __init free_area_init_nodes(unsigned long
> *max_zone_pfn)
> > >
> > >         /* Print out the early node map */
> > >         pr_info("Early memory node ranges\n");
> > > -       for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn,
> &nid)
> > > +       for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn,
> &nid) {
> > >                 pr_info("  node %3d: [mem %#018Lx-%#018Lx]\n", nid,
> > >                         (u64)start_pfn << PAGE_SHIFT,
> > >                         ((u64)end_pfn << PAGE_SHIFT) - 1);
> > > +               section_active_init(start_pfn, end_pfn - start_pfn);
> > > +       }
> > >
> > >         /* Initialise every node */
> > >         mminit_verify_pageflags_layout();
> > > diff --git a/mm/sparse.c b/mm/sparse.c
> > > index f87de7ad32c8..5ef2f884c4e1 100644
> > > --- a/mm/sparse.c
> > > +++ b/mm/sparse.c
> > > @@ -210,6 +210,54 @@ static inline unsigned long
> first_present_section_nr(void)
> > >         return next_present_section_nr(-1);
> > >  }
> > >
> > > +static unsigned long section_active_mask(unsigned long pfn,
> > > +               unsigned long nr_pages)
> > > +{
> > > +       int idx_start, idx_size;
> > > +       phys_addr_t start, size;
> > > +
> > > +       if (!nr_pages)
> > > +               return 0;
> > > +
> > > +       start = PFN_PHYS(pfn);
> > > +       size = PFN_PHYS(min(nr_pages, PAGES_PER_SECTION
> > > +                               - (pfn & ~PAGE_SECTION_MASK)));
> > > +       size = ALIGN(size, SECTION_ACTIVE_SIZE);
> > > +
> > > +       idx_start = section_active_index(start);
> > > +       idx_size = section_active_index(size);
> > > +
> > > +       if (idx_size == 0)
> > > +               return -1;
> > > +       return ((1UL << idx_size) - 1) << idx_start;
> > > +}
> > > +
> > > +void section_active_init(unsigned long pfn, unsigned long nr_pages)
> > > +{
> > > +       int end_sec = pfn_to_section_nr(pfn + nr_pages - 1);
> > > +       int i, start_sec = pfn_to_section_nr(pfn);
> > > +
> > > +       if (!nr_pages)
> > > +               return;
> > > +
> > > +       for (i = start_sec; i <= end_sec; i++) {
> > > +               struct mem_section *ms;
> > > +               unsigned long mask;
> > > +               unsigned long pfns;
> > > +
> > > +               pfns = min(nr_pages, PAGES_PER_SECTION
> > > +                               - (pfn & ~PAGE_SECTION_MASK));
> > > +               mask = section_active_mask(pfn, pfns);
> > > +
> > > +               ms = __nr_to_section(i);
> > > +               pr_debug("%s: sec: %d mask: %#018lx\n", __func__, i,
> mask);
> > > +               ms->usage->map_active = mask;
> > > +
> > > +               pfn += pfns;
> > > +               nr_pages -= pfns;
> > > +       }
> > > +}
> >
> > For some reasons the above code is confusing to me. It seems all the
> > code supposed to do is set all map_active to -1, and trim the first
> > and last sections (can be the same section of course). So, I would
> > replace the above two functions with one function like this:
> >
> > void section_active_init(unsigned long pfn, unsigned long nr_pages)
> > {
> >         int end_sec = pfn_to_section_nr(pfn + nr_pages - 1);
> >         int i, idx, start_sec = pfn_to_section_nr(pfn);
> >         struct mem_section *ms;
> >
> >         if (!nr_pages)
> >                 return;
> >
> >         for (i = start_sec; i <= end_sec; i++) {
> >                 ms = __nr_to_section(i);
> >                 ms->usage->map_active = ~0ul;
> >         }
> >
> >         /* Might need to trim active pfns from the beginning and end */
> >         idx = section_active_index(PFN_PHYS(pfn));
> >         ms = __nr_to_section(start_sec);
> >         ms->usage->map_active &= (~0ul << idx);
> >
> >         idx = section_active_index(PFN_PHYS(pfn + nr_pages -1));
> >         ms = __nr_to_section(end_sec);
> >         ms->usage->map_active &= (~0ul >> (BITS_PER_LONG - idx - 1));
> > }
>
> I like the cleanup, but one of the fixes in v7 resulted in the
> realization that a given section may be populated twice at init time.
> For example, enabling that pr_debug() yields:
>
>     section_active_init: sec: 12 mask: 0x00000003ffffffff
>     section_active_init: sec: 12 mask: 0xe000000000000000
>
> So, the implementation can't blindly clear bits based on the current
> parameters. However, I'm switching this code over to use bitmap_*()
> helpers which should help with the readability.
>

Yes, bitmap_* will help, and I assume you will also make active_map size
scalable?

I will take another look at version 8.


Thank you,
Pasha

[-- Attachment #2: Type: text/html, Size: 12008 bytes --]