On Sat 18-06-16 12:11:19, KarimAllah Ahmed wrote:
> When sparse memory model is used an array of memory sections is created to
> track each block of contiguous physical pages. Each element of this array
> contains PAGES_PER_SECTION pages. During the creation of this array the actual
> boundaries of the memory block is lost, so the whole block is either
> considered
> as present or not.
>
> pfn_valid() in the sparse memory configuration checks which memory sections
> the
> pfn belongs to then checks whether it's present or not. This yields
> sub-optimal
> results when the available memory doesn't cover the whole memory section,
> because pfn_valid will return 'true' even for the unavailable pfns at the
> boundaries of the memory section.
Please be more verbose of _why_ the patch is needed. Why those
"sub-optimal results" matter?
> Cc: Andrew Morton <a...@linux-foundation.org>
> Cc: Mel Gorman <mgor...@techsingularity.net>
> Cc: Vlastimil Babka <vba...@suse.cz>
> Cc: Michal Hocko <mho...@suse.com>
> Cc: Johannes Weiner <han...@cmpxchg.org>
> Cc: Yaowei Bai <baiyao...@cmss.chinamobile.com>
> Cc: Dan Williams <dan.j.willi...@intel.com>
> Cc: Joe Perches <j...@perches.com>
> Cc: Tejun Heo <t...@kernel.org>
> Cc: Anthony Liguori <aligu...@amazon.com>
> Cc: linux...@kvack.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: KarimAllah Ahmed <karah...@amazon.de>
> Signed-off-by: Jan H. Schönherr <jscho...@amazon.de>
> ---
> include/linux/mmzone.h | 22 ++++++++++++++++------
> mm/sparse.c | 37 ++++++++++++++++++++++++++++++++++++-
> 2 files changed, 52 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 02069c2..f76a0e1 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1067,8 +1067,12 @@ struct mem_section {
> * section. (see page_ext.h about this.)
> */
> struct page_ext *page_ext;
> - unsigned long pad;
> + unsigned long pad[3];
> #endif
> +
> + unsigned long first_pfn;
> + unsigned long last_pfn;
> +
> /*
> * WARNING: mem_section must be a power-of-2 in size for the
> * calculation and use of SECTION_ROOT_MASK to make sense.
> @@ -1140,23 +1144,29 @@ static inline int valid_section_nr(unsigned long nr)
>
> static inline struct mem_section *__pfn_to_section(unsigned long pfn)
> {
> + if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
> + return NULL;
> +
> return __nr_to_section(pfn_to_section_nr(pfn));
> }
>
> #ifndef CONFIG_HAVE_ARCH_PFN_VALID
> static inline int pfn_valid(unsigned long pfn)
> {
> - if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
> + struct mem_section *ms;
> +
> + ms = __pfn_to_section(pfn);
> +
> + if (ms && !(ms->first_pfn <= pfn && ms->last_pfn >= pfn))
> return 0;
> - return valid_section(__nr_to_section(pfn_to_section_nr(pfn)));
> +
> + return valid_section(ms);
> }
> #endif
>
> static inline int pfn_present(unsigned long pfn)
> {
> - if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
> - return 0;
> - return present_section(__nr_to_section(pfn_to_section_nr(pfn)));
> + return present_section(__pfn_to_section(pfn));
> }
>
> /*
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 5d0cf45..3c91837 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -166,24 +166,59 @@ void __meminit mminit_validate_memmodel_limits(unsigned
> long *start_pfn,
> }
> }
>
> +static int __init
> +overlaps(u64 start1, u64 end1, u64 start2, u64 end2)
> +{
> + u64 start, end;
> +
> + start = max(start1, start2);
> + end = min(end1, end2);
> + return start <= end;
> +}
> +
> /* Record a memory area against a node. */
> void __init memory_present(int nid, unsigned long start, unsigned long end)
> {
> + unsigned long first_pfn = start;
> unsigned long pfn;
>
> start &= PAGE_SECTION_MASK;
> mminit_validate_memmodel_limits(&start, &end);
> for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION) {
> unsigned long section = pfn_to_section_nr(pfn);
> + unsigned long last_pfn = min(pfn + PAGES_PER_SECTION, end) - 1;
> struct mem_section *ms;
>
> sparse_index_init(section, nid);
> set_section_nid(section, nid);
>
> ms = __nr_to_section(section);
> - if (!ms->section_mem_map)
> + if (!ms->section_mem_map) {
> ms->section_mem_map = sparse_encode_early_nid(nid) |
> SECTION_MARKED_PRESENT;
> + } else {
> + /* Merge the two regions */
> + WARN_ON(sparse_early_nid(ms) != nid);
> +
> + /*
> + * If they don't overlap there will be a hole in
> + * between where meta-data says it's valid even though
> + * it's not.
> + */
> + if (!overlaps(first_pfn, last_pfn + 1,
> + ms->first_pfn, ms->last_pfn + 1)) {
> + pr_info("Merging non-contiguous pfn ranges
> 0x%lx-0x%lx and 0x%lx-0x%lx\n",
> + ms->first_pfn, ms->last_pfn,
> + first_pfn, last_pfn);
> + }
> + first_pfn = min(first_pfn, ms->first_pfn);
> + last_pfn = max(last_pfn, ms->last_pfn);
> + }
> +
> + ms->first_pfn = first_pfn;
> + ms->last_pfn = last_pfn;
> +
> + first_pfn = pfn + PAGES_PER_SECTION;
> }
> }
>
> --
> 2.8.2
>
--
Michal Hocko
SUSE Labs
