kernel/sysctl.c is a kitchen sink where everyone leaves their dirty
dishes, this makes it very difficult to maintain.

To help with this maintenance let's start by moving sysctls to places
where they actually belong.  The proc sysctl maintainers do not want to
know what sysctl knobs you wish to add for your own piece of code, we just
care about the core logic.

So move the page-writeback sysctls to its own file.

[akpm@linux-foundation.org: coding-style cleanups]

akpm@linux-foundation.org: fix CONFIG_SYSCTL=n warnings]
Link: https://lkml.kernel.org/r/20220129012955.26594-1-zhanglianjie@uniontech.comSigned-off-by: Nzhanglianjie <zhanglianjie@uniontech.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Iurii Zaikin <yzaikin@google.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLuis Chamberlain <mcgrof@kernel.org>