linux-kernel - Re: [tip:x86/mm] mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM

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Date:   Thu, 2 Nov 2017 17:12:11 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>, hpa@...or.com,
        Andrew Morton <akpm@...ux-foundation.org>, gorcunov@...nvz.org,
        luto@...capital.net, bp@...e.de,
        open list <linux-kernel@...r.kernel.org>,
        torvalds@...ux-foundation.org, Will Deacon <Will.Deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: [tip:x86/mm] mm/sparsemem: Allocate mem_section at runtime for
 CONFIG_SPARSEMEM_EXTREME=y

On Thu, Nov 02, 2017 at 01:42:42PM +0000, Sudeep Holla wrote:
> 
> 
> On 02/11/17 13:34, Kirill A. Shutemov wrote:
> > On Thu, Nov 02, 2017 at 12:31:54PM +0000, Sudeep Holla wrote:
> >> (+Will, Catalin)
> >>
> >> On Fri, Oct 20, 2017 at 1:27 PM, tip-bot for Kirill A. Shutemov
> >> <tipbot@...or.com> wrote:
> >>> Commit-ID:  83e3c48729d9ebb7af5a31a504f3fd6aff0348c4
> >>> Gitweb:     https://git.kernel.org/tip/83e3c48729d9ebb7af5a31a504f3fd6aff0348c4
> >>> Author:     Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> >>> AuthorDate: Fri, 29 Sep 2017 17:08:16 +0300
> >>> Committer:  Ingo Molnar <mingo@...nel.org>
> >>> CommitDate: Fri, 20 Oct 2017 13:07:09 +0200
> >>>
> >>> mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y
> >>>
> >>> Size of the mem_section[] array depends on the size of the physical address space.
> >>>
> >>> In preparation for boot-time switching between paging modes on x86-64
> >>> we need to make the allocation of mem_section[] dynamic, because otherwise
> >>> we waste a lot of RAM: with CONFIG_NODE_SHIFT=10, mem_section[] size is 32kB
> >>> for 4-level paging and 2MB for 5-level paging mode.
> >>>
> >>> The patch allocates the array on the first call to sparse_memory_present_with_active_regions().
> >>>
> >>
> >> I am seeing a boot failure with this patch in linux-next today(20171102)
> > 
> > Could you share the kernel config?
> > 
> 
> It's the default config on arm64. Generated file is almost 160kB, I will
> send it to you off-list.
> 
> > Have you bisected the failure to the commit?
> > 
> I just reverted this commit as I suspected that and it boots fine after
> the revert.

Could you try the patch below instead?

>From 4a9d843f9d939d958612b0079ebe5743f265e1e0 Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Date: Thu, 2 Nov 2017 17:02:29 +0300
Subject: [PATCH] mm, sparse: Fix boot on arm64

Since 83e3c48729d9 ("mm/sparsemem: Allocate mem_section at runtime for
CONFIG_SPARSEMEM_EXTREME=y") we allocate mem_section dynamically in
sparse_memory_present_with_active_regions(). But some architectures, like
arm64, don't use the routine to initialize sparsemem.

Let's move the initialization into memory_present() it should cover all
architectures.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Fixes: 83e3c48729d9 ("mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y")
---
 mm/page_alloc.c | 10 ----------
 mm/sparse.c     | 10 ++++++++++
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8dfd13f724d9..77e4d3c5c57b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5646,16 +5646,6 @@ void __init sparse_memory_present_with_active_regions(int nid)
 	unsigned long start_pfn, end_pfn;
 	int i, this_nid;
 
-#ifdef CONFIG_SPARSEMEM_EXTREME
-	if (!mem_section) {
-		unsigned long size, align;
-
-		size = sizeof(struct mem_section) * NR_SECTION_ROOTS;
-		align = 1 << (INTERNODE_CACHE_SHIFT);
-		mem_section = memblock_virt_alloc(size, align);
-	}
-#endif
-
 	for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, &this_nid)
 		memory_present(this_nid, start_pfn, end_pfn);
 }
diff --git a/mm/sparse.c b/mm/sparse.c
index b00a97398795..d294148ba395 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -206,6 +206,16 @@ void __init memory_present(int nid, unsigned long start, unsigned long end)
 {
 	unsigned long pfn;
 
+#ifdef CONFIG_SPARSEMEM_EXTREME
+	if (unlikely(!mem_section)) {
+		unsigned long size, align;
+
+		size = sizeof(struct mem_section) * NR_SECTION_ROOTS;
+		align = 1 << (INTERNODE_CACHE_SHIFT);
+		mem_section = memblock_virt_alloc(size, align);
+	}
+#endif
+
 	start &= PAGE_SECTION_MASK;
 	mminit_validate_memmodel_limits(&start, &end);
 	for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION) {
-- 
 Kirill A. Shutemov