linux-kernel - [PATCH v2 1/3] mm: sparse: pass section_nr to section_mark

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Date:   Mon,  5 Jul 2021 17:55:36 +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 v2 1/3] mm: sparse: pass section_nr to section_mark_present

With CONFIG_SPARSEMEM_EXTREME enabled, __section_nr() which converts
mem_section to section_nr could 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).

Let's pass section_nr instead of mem_section ptr to
section_mark_present() in order to reduce needless iterations.

Signed-off-by: Ohhoon Kwon <ohoono.kwon@...sung.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Acked-by: Mike Rapoport <rppt@...ux.ibm.com>
Reviewed-by: David Hildenbrand <david@...hat.com>
---
 mm/sparse.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/mm/sparse.c b/mm/sparse.c
index 6326cdf36c4f..b4fae2fc6276 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -187,13 +187,14 @@ void __meminit mminit_validate_memmodel_limits(unsigned long *start_pfn,
  * those loops early.
  */
 unsigned long __highest_present_section_nr;
-static void section_mark_present(struct mem_section *ms)
+static void section_mark_present(unsigned long section_nr)
 {
-	unsigned long section_nr = __section_nr(ms);
+	struct mem_section *ms;
 
 	if (section_nr > __highest_present_section_nr)
 		__highest_present_section_nr = section_nr;
 
+	ms = __nr_to_section(section_nr);
 	ms->section_mem_map |= SECTION_MARKED_PRESENT;
 }
 
@@ -280,7 +281,7 @@ static void __init memory_present(int nid, unsigned long start, unsigned long en
 		if (!ms->section_mem_map) {
 			ms->section_mem_map = sparse_encode_early_nid(nid) |
 							SECTION_IS_ONLINE;
-			section_mark_present(ms);
+			section_mark_present(section);
 		}
 	}
 }
@@ -934,7 +935,7 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
 
 	ms = __nr_to_section(section_nr);
 	set_section_nid(section_nr, nid);
-	section_mark_present(ms);
+	section_mark_present(section_nr);
 
 	/* Align memmap to section boundary in the subsection case */
 	if (section_nr_to_pfn(section_nr) != start_pfn)
-- 
2.17.1