On Tue, May 25, 2021 at 3:55 PM David Hildenbrand [off-list ref] wrote:

On 17.05.21 13:20, Dong Aisheng wrote:

quoted

In order to distinguish the struct mem_section for a better code
readability and align with kernel doc [1] name below, change the
global mem section name to 'mem_sections' from 'mem_section'.

[1] Documentation/vm/memory-model.rst
"The `mem_section` objects are arranged in a two-dimensional array
called `mem_sections`."

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Young <redacted>
Cc: Baoquan He <redacted>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: kexec@lists.infradead.org
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
---
  include/linux/mmzone.h | 10 +++++-----
  kernel/crash_core.c    |  4 ++--
  mm/sparse.c            | 16 ++++++++--------
  3 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index fc23e36cb165..b348a06915c5 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h

@@ -1297,9 +1297,9 @@ struct mem_section {
  #define SECTION_ROOT_MASK   (SECTIONS_PER_ROOT - 1)

  #ifdef CONFIG_SPARSEMEM_EXTREME
-extern struct mem_section **mem_section;
+extern struct mem_section **mem_sections;
  #else
-extern struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT];
+extern struct mem_section mem_sections[NR_SECTION_ROOTS][SECTIONS_PER_ROOT];
  #endif

  static inline unsigned long *section_to_usemap(struct mem_section *ms)

@@ -1310,12 +1310,12 @@ static inline unsigned long *section_to_usemap(struct mem_section *ms)
  static inline struct mem_section *__nr_to_section(unsigned long nr)
  {
  #ifdef CONFIG_SPARSEMEM_EXTREME
-     if (!mem_section)
+     if (!mem_sections)
              return NULL;
  #endif
-     if (!mem_section[SECTION_NR_TO_ROOT(nr)])
+     if (!mem_sections[SECTION_NR_TO_ROOT(nr)])
              return NULL;
-     return &mem_section[SECTION_NR_TO_ROOT(nr)][nr & SECTION_ROOT_MASK];
+     return &mem_sections[SECTION_NR_TO_ROOT(nr)][nr & SECTION_ROOT_MASK];
  }
  extern unsigned long __section_nr(struct mem_section *ms);
  extern size_t mem_section_usage_size(void);

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 29cc15398ee4..fb1180d81b5a 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c

@@ -414,8 +414,8 @@ static int __init crash_save_vmcoreinfo_init(void)
      VMCOREINFO_SYMBOL(contig_page_data);
  #endif
  #ifdef CONFIG_SPARSEMEM
-     VMCOREINFO_SYMBOL_ARRAY(mem_section);
-     VMCOREINFO_LENGTH(mem_section, NR_SECTION_ROOTS);
+     VMCOREINFO_SYMBOL_ARRAY(mem_sections);
+     VMCOREINFO_LENGTH(mem_sections, NR_SECTION_ROOTS);
      VMCOREINFO_STRUCT_SIZE(mem_section);
      VMCOREINFO_OFFSET(mem_section, section_mem_map);
      VMCOREINFO_NUMBER(MAX_PHYSMEM_BITS);

diff --git a/mm/sparse.c b/mm/sparse.c
index df4418c12f04..a96e7e65475f 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c

@@ -24,12 +24,12 @@
   * 1) mem_section   - memory sections, mem_map's for valid memory
   */
  #ifdef CONFIG_SPARSEMEM_EXTREME
-struct mem_section **mem_section;
+struct mem_section **mem_sections;
  #else
-struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT]
+struct mem_section mem_sections[NR_SECTION_ROOTS][SECTIONS_PER_ROOT]
      ____cacheline_internodealigned_in_smp;
  #endif
-EXPORT_SYMBOL(mem_section);
+EXPORT_SYMBOL(mem_sections);

  #ifdef NODE_NOT_IN_PAGE_FLAGS
  /*

@@ -91,14 +91,14 @@ static int __meminit sparse_index_init(unsigned long section_nr, int nid)
       *
       * The mem_hotplug_lock resolves the apparent race below.
       */
-     if (mem_section[root])
+     if (mem_sections[root])
              return 0;

      section = sparse_index_alloc(nid);
      if (!section)
              return -ENOMEM;

-     mem_section[root] = section;
+     mem_sections[root] = section;

      return 0;
  }

@@ -131,7 +131,7 @@ unsigned long __section_nr(struct mem_section *ms)
  #else
  unsigned long __section_nr(struct mem_section *ms)
  {
-     return (unsigned long)(ms - mem_section[0]);
+     return (unsigned long)(ms - mem_sections[0]);
  }
  #endif

@@ -286,8 +286,8 @@ static void __init memblocks_present(void)
  #ifdef CONFIG_SPARSEMEM_EXTREME
      size = sizeof(struct mem_section *) * NR_SECTION_ROOTS;
      align = 1 << (INTERNODE_CACHE_SHIFT);
-     mem_section = memblock_alloc(size, align);
-     if (!mem_section)
+     mem_sections = memblock_alloc(size, align);
+     if (!mem_sections)
              panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
                    __func__, size, align);
  #endif

Smells like unnecessary code churn. I'd rather just fix the doc because
it doesn't really improve readability IMHO.

In  practice I feel it does affect readability that the global
mem_section pointer is mixed
with struct mem_section names which results in:
1. hard to quickly jump between global mem_section operation in a
single source file.
    e.g. by VIM hotkey of search
2. hard to quickly identify all global mem_section operations in
global source files
    by tools, e.g. cscope, grep

This does cause troubles if users want to quickly go through and
understand the code.

Regards
Aisheng

Anyhow, just my 2 cents.

--
Thanks,

David / dhildenb