Re: [PATCH -next] mm/hotplug: skip bad PFNs from pfn_to_online_page()
From: Aneesh Kumar K.V
Date: Fri Jun 14 2019 - 12:30:57 EST
On 6/14/19 9:52 PM, Dan Williams wrote:
On Fri, Jun 14, 2019 at 9:18 AM Aneesh Kumar K.V
<aneesh.kumar@xxxxxxxxxxxxx> 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
That should be SECTION_SIZE_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.
persistent memory namespaces are not portable across archs because they
have PAGE_SIZE dependency. Then we have dependencies like the page size
with which we map the vmemmap area. Why not let the arch
arch decide the SUBSECTION_SHIFT and default to one subsection per
section if arch is not enabled to work with subsection.
-aneesh