On Fri, 5 Jan 2018 14:02:35 +0100 Oscar Salvador <osalvador@xxxxxxxxxxxxxxxxxx> wrote:
> 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, but I wanted to see what you guys think.
Presumably the CONFIG_PAGE_EXTENSION users should `select'
CONFIG_PAGE_EXTENSION so the situation doesn't arise.
(or does it? I have a vague memory that if CONFIG_A selects CONFIG_B
and you then set CONFIG_A=n, CONFIG_B remains enabled?)
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