docs: admin-guide: remove obsolete advice related to SLAB allocator

Commit 1db9d06 ("mm/slab: remove CONFIG_SLAB from all Kconfig and
Makefile") removes the config SLAB and makes the SLUB allocator the only
default allocator in the kernel. Hence, the advice on reducing OS jitter
due to kworker kernel threads to build with CONFIG_SLUB instead of
CONFIG_SLAB is obsolete.

Remove the obsolete advice to build with SLUB instead of SLAB.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20231130095515.21586-1-lukas.bulwahn@gmail.com

Author: bulwahn

Documentation/admin-guide/kernel-per-CPU-kthreads.rst

@@ -243,13 +243,9 @@ To reduce its OS jitter, do any of the following:
 3.	Do any of the following needed to avoid jitter that your
 	application cannot tolerate:
 
-	a.	Build your kernel with CONFIG_SLUB=y rather than
-		CONFIG_SLAB=y, thus avoiding the slab allocator's periodic
-		use of each CPU's workqueues to run its cache_reap()
-		function.
-	b.	Avoid using oprofile, thus avoiding OS jitter from
+	a.	Avoid using oprofile, thus avoiding OS jitter from
 		wq_sync_buffer().
-	c.	Limit your CPU frequency so that a CPU-frequency
+	b.	Limit your CPU frequency so that a CPU-frequency
 		governor is not required, possibly enlisting the aid of
 		special heatsinks or other cooling technologies.  If done
 		correctly, and if you CPU architecture permits, you should
@@ -259,7 +255,7 @@ To reduce its OS jitter, do any of the following:
 
 		WARNING:  Please check your CPU specifications to
 		make sure that this is safe on your particular system.
-	d.	As of v3.18, Christoph Lameter's on-demand vmstat workers
+	c.	As of v3.18, Christoph Lameter's on-demand vmstat workers
 		commit prevents OS jitter due to vmstat_update() on
 		CONFIG_SMP=y systems.  Before v3.18, is not possible
 		to entirely get rid of the OS jitter, but you can
@@ -274,20 +270,20 @@ To reduce its OS jitter, do any of the following:
 		(based on an earlier one from Gilad Ben-Yossef) that
 		reduces or even eliminates vmstat overhead for some
 		workloads at https://lore.kernel.org/r/00000140e9dfd6bd-40db3d4f-c1be-434f-8132-7820f81bb586-000000@email.amazonses.com.
-	e.	If running on high-end powerpc servers, build with
+	d.	If running on high-end powerpc servers, build with
 		CONFIG_PPC_RTAS_DAEMON=n.  This prevents the RTAS
 		daemon from running on each CPU every second or so.
 		(This will require editing Kconfig files and will defeat
 		this platform's RAS functionality.)  This avoids jitter
 		due to the rtas_event_scan() function.
 		WARNING:  Please check your CPU specifications to
 		make sure that this is safe on your particular system.
-	f.	If running on Cell Processor, build your kernel with
+	e.	If running on Cell Processor, build your kernel with
 		CBE_CPUFREQ_SPU_GOVERNOR=n to avoid OS jitter from
 		spu_gov_work().
 		WARNING:  Please check your CPU specifications to
 		make sure that this is safe on your particular system.
-	g.	If running on PowerMAC, build your kernel with
+	f.	If running on PowerMAC, build your kernel with
 		CONFIG_PMAC_RACKMETER=n to disable the CPU-meter,
 		avoiding OS jitter from rackmeter_do_timer().