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/ Acked-by: Vlastimil Babka Acked-by: David Hildenbrand (Red Hat) Signed-off-by: Brendan Jackman --- Changes in v2: - Specified section in docs reference - Link to v1: https://lore.kernel.org/all/DF0J58HOVLL4.2E16Q87D2UXRW@google.com/ --- include/linux/gfp_types.h | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h index 3de43b12209ee79f84e7c9c919729303338433ff..814bb2892f99b829fde9b6dce1a317b3f29d01dc 100644 --- a/include/linux/gfp_types.h +++ b/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. --- base-commit: fc2af7a8060126c3a99fc1dfd7c5abd71a4dc81d change-id: 20251219-b4-gfp_atomic-comment-3e5950152139 Best regards, -- Brendan Jackman