mm/slab: rename CONFIG_SLAB to CONFIG_SLAB_DEPRECATED

mm/slab: rename CONFIG_SLAB to CONFIG_SLAB_DEPRECATED

As discussed at LSF/MM [1] [2] and with no objections raised there,
deprecate the SLAB allocator. Rename the user-visible option so that
users with CONFIG_SLAB=y get a new prompt with explanation during make
oldconfig, while make olddefconfig will just switch to SLUB.

In all defconfigs with CONFIG_SLAB=y remove the line so those also
switch to SLUB. Regressions due to the switch should be reported to
linux-mm and slab maintainers.

[1] https://lore.kernel.org/all/4b9fc9c6-b48c-198f-5f80-811a44737e5f@suse.cz/
[2] https://lwn.net/Articles/932201/

Signed-off-by: Vlastimil Babka <[email protected]>
Acked-by: Hyeonggon Yoo <[email protected]>
Acked-by: David Rientjes <[email protected]>
Acked-by: Geert Uytterhoeven <[email protected]> # m68k
Acked-by: Helge Deller <[email protected]> # parisc