From: Dan Williams <dan.j.williams@intel.com>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Oscar Salvador <osalvador@suse.de>, Qian Cai <cai@lca.pw>,
Andrew Morton <akpm@linux-foundation.org>,
Linux MM <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
jmoyer <jmoyer@redhat.com>
Subject: Re: [PATCH -next] mm/hotplug: skip bad PFNs from pfn_to_online_page()
Date: Fri, 14 Jun 2019 09:22:29 -0700 [thread overview]
Message-ID: <CAPcyv4j_QQB8SrhTqL2mnEEHGYCg4H7kYanChiww35k0fwNv8Q@mail.gmail.com> (raw)
In-Reply-To: <c3f2c05d-e42f-c942-1385-664f646ddd33@linux.ibm.com>
On Fri, Jun 14, 2019 at 9:18 AM Aneesh Kumar K.V
<aneesh.kumar@linux.ibm.com> wrote:
>
> On 6/14/19 9:05 PM, Oscar Salvador wrote:
> > On Fri, Jun 14, 2019 at 02:28:40PM +0530, Aneesh Kumar K.V wrote:
> >> Can you check with this change on ppc64. I haven't reviewed this series yet.
> >> I did limited testing with change . Before merging this I need to go
> >> through the full series again. The vmemmap poplulate on ppc64 needs to
> >> handle two translation mode (hash and radix). With respect to vmemap
> >> hash doesn't setup a translation in the linux page table. Hence we need
> >> to make sure we don't try to setup a mapping for a range which is
> >> arleady convered by an existing mapping.
> >>
> >> diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
> >> index a4e17a979e45..15c342f0a543 100644
> >> --- a/arch/powerpc/mm/init_64.c
> >> +++ b/arch/powerpc/mm/init_64.c
> >> @@ -88,16 +88,23 @@ static unsigned long __meminit vmemmap_section_start(unsigned long page)
> >> * which overlaps this vmemmap page is initialised then this page is
> >> * initialised already.
> >> */
> >> -static int __meminit vmemmap_populated(unsigned long start, int page_size)
> >> +static bool __meminit vmemmap_populated(unsigned long start, int page_size)
> >> {
> >> unsigned long end = start + page_size;
> >> start = (unsigned long)(pfn_to_page(vmemmap_section_start(start)));
> >>
> >> - for (; start < end; start += (PAGES_PER_SECTION * sizeof(struct page)))
> >> - if (pfn_valid(page_to_pfn((struct page *)start)))
> >> - return 1;
> >> + for (; start < end; start += (PAGES_PER_SECTION * sizeof(struct page))) {
> >>
> >> - return 0;
> >> + struct mem_section *ms;
> >> + unsigned long pfn = page_to_pfn((struct page *)start);
> >> +
> >> + if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
> >> + return 0;
> >
> > I might be missing something, but is this right?
> > Having a section_nr above NR_MEM_SECTIONS is invalid, but if we return 0 here,
> > vmemmap_populate will go on and populate it.
>
> I should drop that completely. We should not hit that condition at all.
> I will send a final patch once I go through the full patch series making
> sure we are not breaking any ppc64 details.
>
> Wondering why we did the below
>
> #if defined(ARCH_SUBSECTION_SHIFT)
> #define SUBSECTION_SHIFT (ARCH_SUBSECTION_SHIFT)
> #elif defined(PMD_SHIFT)
> #define SUBSECTION_SHIFT (PMD_SHIFT)
> #else
> /*
> * Memory hotplug enabled platforms avoid this default because they
> * either define ARCH_SUBSECTION_SHIFT, or PMD_SHIFT is a constant, but
> * this is kept as a backstop to allow compilation on
> * !ARCH_ENABLE_MEMORY_HOTPLUG archs.
> */
> #define SUBSECTION_SHIFT 21
> #endif
>
> why not
>
> #if defined(ARCH_SUBSECTION_SHIFT)
> #define SUBSECTION_SHIFT (ARCH_SUBSECTION_SHIFT)
> #else
> #define SUBSECTION_SHIFT SECTION_SHIFT
> #endif
>
> ie, if SUBSECTION is not supported by arch we have one sub-section per
> section?
A couple comments:
The only reason ARCH_SUBSECTION_SHIFT exists is because PMD_SHIFT on
PowerPC was a non-constant value. However, I'm planning to remove the
distinction in the next rev of the patches. Jeff rightly points out
that having a variable subsection size per arch will lead to
situations where persistent memory namespaces are not portable across
archs. So I plan to just make SUBSECTION_SHIFT 21 everywhere.
next prev parent reply other threads:[~2019-06-14 16:22 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-12 19:15 [PATCH -next] mm/hotplug: skip bad PFNs from pfn_to_online_page() Qian Cai
2019-06-12 19:37 ` Dan Williams
2019-06-12 19:38 ` Dan Williams
2019-06-12 21:47 ` Qian Cai
2019-06-12 21:52 ` Dan Williams
2019-06-12 23:13 ` Dan Williams
2019-06-13 0:06 ` Dan Williams
2019-06-14 8:58 ` Aneesh Kumar K.V
2019-06-14 14:59 ` Qian Cai
2019-06-14 18:03 ` Dan Williams
2019-06-14 18:57 ` Dan Williams
2019-06-14 19:40 ` Qian Cai
2019-06-14 19:48 ` Dan Williams
2019-06-14 20:43 ` Qian Cai
2019-06-16 15:42 ` Dan Williams
2019-06-17 2:25 ` Qian Cai
2019-06-14 15:35 ` Oscar Salvador
2019-06-14 16:18 ` Aneesh Kumar K.V
2019-06-14 16:22 ` Dan Williams [this message]
2019-06-14 16:26 ` Aneesh Kumar K.V
2019-06-14 16:36 ` Dan Williams
2019-06-14 16:50 ` Aneesh Kumar K.V
2019-06-14 16:55 ` Aneesh Kumar K.V
2019-06-14 17:08 ` Jeff Moyer
2019-06-14 17:14 ` Dan Williams
2019-06-14 17:40 ` Aneesh Kumar K.V
2019-06-16 3:49 ` Aneesh Kumar K.V
2019-06-17 17:21 ` Dan Williams
2019-06-13 18:42 ` Qian Cai
2019-06-14 1:17 ` Dan Williams
2019-06-14 1:29 ` Qian Cai
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