mm/page_ext.c: make page_ext_init a noop when CONFIG_PAGE_EXTENSION but nothing uses it
authorOscar Salvador <osalvador@techadventures.net>
Thu, 1 Feb 2018 00:20:19 +0000 (16:20 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Thu, 1 Feb 2018 01:18:39 +0000 (17:18 -0800)
commit3a45acc0869748d7a650e36377839d849c28a52c
tree74df60d416dc9945a2a63a86e281d53f0fb63793
parent01a6ad9ac80c9b861f63087f81e696f47b481168
mm/page_ext.c: make page_ext_init a noop when CONFIG_PAGE_EXTENSION but nothing uses it

static struct page_ext_operations *page_ext_ops[] always contains debug_guardpage_ops,

static struct page_ext_operations *page_ext_ops[] = {
        &debug_guardpage_ops,
 #ifdef CONFIG_PAGE_OWNER
        &page_owner_ops,
 #endif
...
}

but for it to work, CONFIG_DEBUG_PAGEALLOC must be enabled first.  If
someone has CONFIG_PAGE_EXTENSION, but has none of its users, eg:
(CONFIG_PAGE_OWNER, CONFIG_DEBUG_PAGEALLOC, CONFIG_IDLE_PAGE_TRACKING),
we can shrink page_ext_init() to a simple retq.

  $ size vmlinux  (before patch)
        text      data       bss       dec       hex  filename
    14356698   5681582   1687748  21726028   14b834c  vmlinux

  $ size vmlinux  (after patch)
        text      data       bss       dec       hex  filename
    14356008   5681538   1687748  21725294   14b806e  vmlinux

On the other hand, it might does not even make sense, since if someone
enables CONFIG_PAGE_EXTENSION, I would expect him to enable also at
least one of its users.

Link: http://lkml.kernel.org/r/20180105130235.GA21241@techadventures.net
Signed-off-by: Oscar Salvador <osalvador@techadventures.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Jaewon Kim <jaewon31.kim@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/page_ext.c