From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752827AbcFTIXu (ORCPT ); Mon, 20 Jun 2016 04:23:50 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:34589 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751099AbcFTIXn (ORCPT ); Mon, 20 Jun 2016 04:23:43 -0400 Date: Mon, 20 Jun 2016 10:23:40 +0200 From: Michal Hocko To: KarimAllah Ahmed Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Mel Gorman , Vlastimil Babka , Johannes Weiner , Yaowei Bai , Dan Williams , Joe Perches , Tejun Heo , Anthony Liguori , Jan H =?iso-8859-1?Q?=2E_Sch=F6nherr?= Subject: Re: [PATCH] sparse: Track the boundaries of memory sections for accurate checks Message-ID: <20160620082339.GC4340@dhcp22.suse.cz> References: <1466244679-23824-1-git-send-email-karahmed@amazon.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1466244679-23824-1-git-send-email-karahmed@amazon.de> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > Cc: Mel Gorman > Cc: Vlastimil Babka > Cc: Michal Hocko > Cc: Johannes Weiner > Cc: Yaowei Bai > Cc: Dan Williams > Cc: Joe Perches > Cc: Tejun Heo > Cc: Anthony Liguori > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > Signed-off-by: KarimAllah Ahmed > Signed-off-by: Jan H. Schönherr > --- > 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