linux-kernel - [PATCH 3/3] mm: sparse: remove __section

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Message-Id: <20210702094132.6276-4-ohoono.kwon@samsung.com>
Date:   Fri,  2 Jul 2021 18:41:32 +0900
From:   Ohhoon Kwon <ohoono.kwon@...sung.com>
To:     david@...hat.com, ohoono.kwon@...sung.com,
        akpm@...ux-foundation.org, mhocko@...e.com
Cc:     bhe@...hat.com, rppt@...ux.ibm.com, ohkwon1043@...il.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] mm: sparse: remove __section_nr() function

__section_nr() was used to convert struct mem_section * to section_nr.

With CONFIG_SPARSEMEM_EXTREME enabled, however, __section_nr() can be
costly since it iterates all section roots to check if the given
mem_section is in its range.

On the other hand, __nr_to_section() which converts section_nr to
mem_section can be done in O(1).

The only users of __section_nr() was section_mark_present() and
find_memory_block().

Since I changed both functions to use section_nr directly in the
preceeding patches, let's remove __section_nr() which has no users.

Signed-off-by: Ohhoon Kwon <ohoono.kwon@...sung.com>
---
 include/linux/mmzone.h |  1 -
 mm/sparse.c            | 26 --------------------------
 2 files changed, 27 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 0d53eba1c383..8931f95cf885 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1321,7 +1321,6 @@ static inline struct mem_section *__nr_to_section(unsigned long nr)
 		return NULL;
 	return &mem_section[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/mm/sparse.c b/mm/sparse.c
index 4a2700e9a65f..1b32d15593e4 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -108,32 +108,6 @@ static inline int sparse_index_init(unsigned long section_nr, int nid)
 }
 #endif
 
-#ifdef CONFIG_SPARSEMEM_EXTREME
-unsigned long __section_nr(struct mem_section *ms)
-{
-	unsigned long root_nr;
-	struct mem_section *root = NULL;
-
-	for (root_nr = 0; root_nr < NR_SECTION_ROOTS; root_nr++) {
-		root = __nr_to_section(root_nr * SECTIONS_PER_ROOT);
-		if (!root)
-			continue;
-
-		if ((ms >= root) && (ms < (root + SECTIONS_PER_ROOT)))
-		     break;
-	}
-
-	VM_BUG_ON(!root);
-
-	return (root_nr * SECTIONS_PER_ROOT) + (ms - root);
-}
-#else
-unsigned long __section_nr(struct mem_section *ms)
-{
-	return (unsigned long)(ms - mem_section[0]);
-}
-#endif
-
 /*
  * During early boot, before section_mem_map is used for an actual
  * mem_map, we use section_mem_map to store the section's NUMA
-- 
2.17.1