+ mm-clarify-gfp_atomic-gfp_nowait-doc-comment.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: clarify GFP_ATOMIC/GFP_NOWAIT doc-comment
has been added to the -mm mm-new branch.  Its filename is
     mm-clarify-gfp_atomic-gfp_nowait-doc-comment.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-clarify-gfp_atomic-gfp_nowait-doc-comment.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
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------------------------------------------------------
From: Brendan Jackman <jackmanb@google.com>
Subject: mm: clarify GFP_ATOMIC/GFP_NOWAIT doc-comment
Date: Fri, 19 Dec 2025 11:32:18 +0000

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: Brendan Jackman <jackmanb@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David 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: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/gfp_types.h |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/include/linux/gfp_types.h~mm-clarify-gfp_atomic-gfp_nowait-doc-comment
+++ a/include/linux/gfp_types.h
@@ -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.
_

Patches currently in -mm which might be from jackmanb@google.com are

mm-vmalloc-clarify-why-vmap_range_noflush-might-sleep.patch
mm-clarify-gfp_atomic-gfp_nowait-doc-comment.patch