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mm: Update shuffle documentation to match its current state

Commit 839195352d82 ("mm/shuffle: remove dynamic reconfiguration")
removed the dynamic reconfiguration capabilities from the shuffle page
allocator. This means that, now, we don't have any perspective of an
"autodetection of memory-side-cache" that triggers the enablement of the
shuffle page allocator.

Therefore, let the documentation reflect that the only way to enable
the shuffle page allocator is by setting `page_alloc.shuffle=1`.

Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240422142007.1062231-1-mcanal@igalia.com

authored by

Maíra Canal and committed by
Jonathan Corbet b413f9cd 8af2d1ab

+7 -10
+4 -6
Documentation/admin-guide/kernel-parameters.txt
··· 4169 4169 4170 4170 page_alloc.shuffle= 4171 4171 [KNL] Boolean flag to control whether the page allocator 4172 - should randomize its free lists. The randomization may 4173 - be automatically enabled if the kernel detects it is 4174 - running on a platform with a direct-mapped memory-side 4175 - cache, and this parameter can be used to 4176 - override/disable that behavior. The state of the flag 4177 - can be read from sysfs at: 4172 + should randomize its free lists. This parameter can be 4173 + used to enable/disable page randomization. The state of 4174 + the flag can be read from sysfs at: 4178 4175 /sys/module/page_alloc/parameters/shuffle. 4176 + This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y. 4179 4177 4180 4178 page_owner= [KNL,EARLY] Boot-time page_owner enabling option. 4181 4179 Storage of the information about who allocated
+3 -4
mm/Kconfig
··· 333 333 334 334 While the randomization improves cache utilization it may 335 335 negatively impact workloads on platforms without a cache. For 336 - this reason, by default, the randomization is enabled only 337 - after runtime detection of a direct-mapped memory-side-cache. 338 - Otherwise, the randomization may be force enabled with the 339 - 'page_alloc.shuffle' kernel command line parameter. 336 + this reason, by default, the randomization is not enabled even 337 + if SHUFFLE_PAGE_ALLOCATOR=y. The randomization may be force enabled 338 + with the 'page_alloc.shuffle' kernel command line parameter. 340 339 341 340 Say Y if unsure. 342 341