[PATCH v2 2/4] mm/sparse: Optimize sparse_add_one_section()

[Baoquan He]

Reorder the allocation of usemap and memmap since usemap allocation
is much simpler and easier. Otherwise hard work is done to make
memmap ready, then have to rollback just because of usemap allocation
failure.

And also check if section is present earlier. Then don't bother to
allocate usemap and memmap if yes.

Signed-off-by: Baoquan He <b...@redhat.com>
---
v1->v2:
  Do section existence checking earlier to further optimize code.

 mm/sparse.c | 29 +++++++++++------------------
 1 file changed, 11 insertions(+), 18 deletions(-)

diff --git a/mm/sparse.c b/mm/sparse.c
index b2111f996aa6..f4f34d69131e 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -714,20 +714,18 @@ int __meminit sparse_add_one_section(int nid, unsigned 
long start_pfn,
        ret = sparse_index_init(section_nr, nid);
        if (ret < 0 && ret != -EEXIST)
                return ret;
-       ret = 0;
-       memmap = kmalloc_section_memmap(section_nr, nid, altmap);
-       if (!memmap)
-               return -ENOMEM;
-       usemap = __kmalloc_section_usemap();
-       if (!usemap) {
-               __kfree_section_memmap(memmap, altmap);
-               return -ENOMEM;
-       }
 
        ms = __pfn_to_section(start_pfn);
-       if (ms->section_mem_map & SECTION_MARKED_PRESENT) {
-               ret = -EEXIST;
-               goto out;
+       if (ms->section_mem_map & SECTION_MARKED_PRESENT)
+               return -EEXIST;
+
+       usemap = __kmalloc_section_usemap();
+       if (!usemap)
+               return -ENOMEM;
+       memmap = kmalloc_section_memmap(section_nr, nid, altmap);
+       if (!memmap) {
+               kfree(usemap);
+               return  -ENOMEM;
        }
 
        /*
@@ -739,12 +737,7 @@ int __meminit sparse_add_one_section(int nid, unsigned 
long start_pfn,
        section_mark_present(ms);
        sparse_init_one_section(ms, section_nr, memmap, usemap);
 
-out:
-       if (ret < 0) {
-               kfree(usemap);
-               __kfree_section_memmap(memmap, altmap);
-       }
-       return ret;
+       return 0;
 }
 
 #ifdef CONFIG_MEMORY_HOTREMOVE
-- 
2.17.2