linux-kernel - [PATCH V2 3/6] mm/sparse: move mem_sections allocation out of memory

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Date:   Mon, 31 May 2021 17:19:05 +0800
From:   Dong Aisheng <aisheng.dong@....com>
To:     linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, dongas86@...il.com,
        Dong Aisheng <aisheng.dong@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...nel.org>
Subject: [PATCH V2 3/6] mm/sparse: move mem_sections allocation out of memory_present()

The only path to call memory_present() is from memblocks_present().
The struct mem_section **mem_section only needs to be initialized once,
so no need put the initialization/allocation code in memory_present()
which will be called multiple times for each section.

After moving, the 'unlikely' condition statement becomes to be
meaningless as it's only initialized one time, so dropped as well.

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Mike Rapoport <rppt@...nel.org>
Signed-off-by: Dong Aisheng <aisheng.dong@....com>
---
ChangeLog:
v1->v2:
 * split into a helper function and called directly from sparse_init
---
 mm/sparse.c | 29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)

diff --git a/mm/sparse.c b/mm/sparse.c
index 408b737e168e..d02ee6bb7cbc 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -60,6 +60,18 @@ static inline void set_section_nid(unsigned long section_nr, int nid)
 #endif
 
 #ifdef CONFIG_SPARSEMEM_EXTREME
+static void __init sparse_alloc_section_roots(void)
+{
+	unsigned long size, align;
+
+	size = sizeof(struct mem_section *) * NR_SECTION_ROOTS;
+	align = 1 << (INTERNODE_CACHE_SHIFT);
+	mem_section = memblock_alloc(size, align);
+	if (!mem_section)
+		panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
+		      __func__, size, align);
+}
+
 static noinline struct mem_section __ref *sparse_index_alloc(int nid)
 {
 	struct mem_section *section = NULL;
@@ -107,6 +119,8 @@ static inline int sparse_index_init(unsigned long section_nr, int nid)
 {
 	return 0;
 }
+
+static inline void sparse_alloc_section_roots(void) {}
 #endif
 
 #ifdef CONFIG_SPARSEMEM_EXTREME
@@ -254,19 +268,6 @@ static void __init memory_present(int nid, unsigned long start, unsigned long en
 {
 	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_alloc(size, align);
-		if (!mem_section)
-			panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
-			      __func__, size, align);
-	}
-#endif
-
 	start &= PAGE_SECTION_MASK;
 	mminit_validate_memmodel_limits(&start, &end);
 	for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION) {
@@ -582,6 +583,8 @@ void __init sparse_init(void)
 	unsigned long pnum_end, pnum_begin, map_count = 1;
 	int nid_begin;
 
+	sparse_alloc_section_roots();
+
 	memblocks_present();
 
 	pnum_begin = first_present_section_nr();
-- 
2.25.1