On 6/20/16, 10:23 AM, "Michal Hocko" <mhocko@xxxxxxxxxx> wrote: 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? Does this make sense to you ? > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> > Cc: Vlastimil Babka <vbabka@xxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> > Cc: Johannes Weiner <hannes@xxxxxxxxxxx> > Cc: Yaowei Bai <baiyaowei@xxxxxxxxxxxxxxxxxxxx> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx> > Cc: Joe Perches <joe@xxxxxxxxxxx> > Cc: Tejun Heo <tj@xxxxxxxxxx> > Cc: Anthony Liguori <aliguori@xxxxxxxxxx> > Cc: linux-mm@xxxxxxxxx > Cc: linux-kernel@xxxxxxxxxxxxxxx > Signed-off-by: KarimAllah Ahmed <karahmed@xxxxxxxxx> > Signed-off-by: Jan H. Schönherr <jschoenh@xxxxxxxxx> > --- > 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 Amazon Development Center Germany GmbH Berlin - Dresden - Aachen main office: Krausenstr. 38, 10117 Berlin Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger Ust-ID: DE289237879 Eingetragen am Amtsgericht Charlottenburg HRB 149173 B ��.n������g����a����&ޖ)���)��h���&������梷�����Ǟ�m������)������^�����������v���O��zf������