linux-kernel - Re: [PATCHv4 01/14] mm/sparsemem: Allocate mem_section at runtime for SPARSEMEM

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Date:   Mon, 14 Aug 2017 17:29:08 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...capital.net>,
        Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 01/14] mm/sparsemem: Allocate mem_section at runtime
 for SPARSEMEM_EXTREME

On Tue, Aug 08, 2017 at 12:54:02PM +0000, Kirill A. Shutemov wrote:
> Size of mem_section array depends on size of physical address space.
> 
> In preparation for boot-time switching between paging modes on x86-64
> we need to make allocation of mem_section dynamic.
> 
> The patch allocates the array on the first call to
> sparse_memory_present_with_active_regions().
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

Fixup for the patch:

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index c8eb668eab79..9799c2c58ce6 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1144,6 +1144,10 @@ extern struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT];
 
 static inline struct mem_section *__nr_to_section(unsigned long nr)
 {
+#ifdef CONFIG_SPARSEMEM_EXTREME
+        if (!mem_section)
+                return NULL;
+#endif
 	if (!mem_section[SECTION_NR_TO_ROOT(nr)])
 		return NULL;
 	return &mem_section[SECTION_NR_TO_ROOT(nr)][nr & SECTION_ROOT_MASK];
-- 
 Kirill A. Shutemov