Commit 241b3a09 authored by Brendan Jackman's avatar Brendan Jackman Committed by Andrew Morton
Browse files

mm: clarify GFP_ATOMIC/GFP_NOWAIT doc-comment 

The current description of contexts where it's invalid to make GFP_ATOMIC
and GFP_NOWAIT calls is rather vague.

Replace this with a direct description of the actual contexts of concern
and refer to the RT docs where this is explained more discursively.

While rejigging this prose, also move the documentation of GFP_NOWAIT to
the GFP_NOWAIT section.

Link: https://lore.kernel.org/all/d912480a-5229-4efe-9336-b31acded30f5@suse.cz/
Link: https://lkml.kernel.org/r/20251219-b4-gfp_atomic-comment-v2-1-4c4ce274c2b6@google.com


Signed-off-by: default avatarBrendan Jackman <jackmanb@google.com>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Acked-by: default avatarDavid Hildenbrand (Red Hat) <david@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 7969f305

include/linux/gfp_types.h

+5 −2
Original line number Diff line number Diff line
@@ -309,8 +309,10 @@ enum { 
 *

 * %GFP_ATOMIC users can not sleep and need the allocation to succeed. A lower

 * watermark is applied to allow access to "atomic reserves".

 * The current implementation doesn't support NMI and few other strict

 * non-preemptive contexts (e.g. raw_spin_lock). The same applies to %GFP_NOWAIT.

 * The current implementation doesn't support NMI, nor contexts that disable

 * preemption under PREEMPT_RT. This includes raw_spin_lock() and plain

 * preempt_disable() - see "Memory allocation" in

 * Documentation/core-api/real-time/differences.rst for more info.

 *

 * %GFP_KERNEL is typical for kernel-internal allocations. The caller requires

 * %ZONE_NORMAL or a lower zone for direct access but can direct reclaim.
@@ -321,6 +323,7 @@ enum { 
 * %GFP_NOWAIT is for kernel allocations that should not stall for direct

 * reclaim, start physical IO or use any filesystem callback.  It is very

 * likely to fail to allocate memory, even for very small allocations.

 * The same restrictions on calling contexts apply as for %GFP_ATOMIC.

 *

 * %GFP_NOIO will use direct reclaim to discard clean pages or slab pages

 * that do not require the starting of any physical IO.