[PATCH] rust: alloc: add GFP_NOIO flag

[PATCH] rust: alloc: add GFP_NOIO flag

[Andreas Hindborg]

Add an abstraction for the `GFP_NOIO` flag. This flag signals that the
caller requires allocation to complete without triggering any block device
IO.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/bindings/bindings_helper.h | 1 +
 rust/kernel/alloc.rs            | 4 ++++
 2 files changed, 5 insertions(+)

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index a067038b4b422..3910ecc5c34cf 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -106,6 +106,7 @@ const size_t RUST_CONST_HELPER_PAGE_SIZE = PAGE_SIZE;
 const gfp_t RUST_CONST_HELPER_GFP_ATOMIC = GFP_ATOMIC;
 const gfp_t RUST_CONST_HELPER_GFP_KERNEL = GFP_KERNEL;
 const gfp_t RUST_CONST_HELPER_GFP_KERNEL_ACCOUNT = GFP_KERNEL_ACCOUNT;
+const gfp_t RUST_CONST_HELPER_GFP_NOIO = GFP_NOIO;
 const gfp_t RUST_CONST_HELPER_GFP_NOWAIT = GFP_NOWAIT;
 const gfp_t RUST_CONST_HELPER___GFP_ZERO = __GFP_ZERO;
 const gfp_t RUST_CONST_HELPER___GFP_HIGHMEM = ___GFP_HIGHMEM;
diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
index e38720349dcf7..5f6a0f7e99c03 100644
--- a/rust/kernel/alloc.rs
+++ b/rust/kernel/alloc.rs
@@ -99,6 +99,10 @@ pub mod flags {
     /// The same as [`GFP_KERNEL`], except the allocation is accounted to kmemcg.
     pub const GFP_KERNEL_ACCOUNT: Flags = Flags(bindings::GFP_KERNEL_ACCOUNT);
 
+    /// [`GFP_NOIO`] will use direct reclaim to discard clean pages or slab
+    /// pages that do not require the starting of any physical IO.
+    pub const GFP_NOIO: Flags = Flags(bindings::GFP_NOIO);
+
     /// 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.

---
base-commit: 63804fed149a6750ffd28610c5c1c98cce6bd377
change-id: 20260128-gfp-noio-fbd41e135088

Best regards,
-- 
Andreas Hindborg <a.hindborg@kernel.org>

Re: [PATCH] rust: alloc: add GFP_NOIO flag

[Danilo Krummrich]

On Wed Jan 28, 2026 at 7:37 PM CET, Andreas Hindborg wrote:
> +    /// [`GFP_NOIO`] will use direct reclaim to discard clean pages or slab
> +    /// pages that do not require the starting of any physical IO.
> +    pub const GFP_NOIO: Flags = Flags(bindings::GFP_NOIO);

How do you use this? What about abstractions for memalloc_noio_{save,restore}()
instead?

Re: [PATCH] rust: alloc: add GFP_NOIO flag

[Andreas Hindborg]

"Danilo Krummrich" <dakr@kernel.org> writes:

> On Wed Jan 28, 2026 at 7:37 PM CET, Andreas Hindborg wrote:
>> +    /// [`GFP_NOIO`] will use direct reclaim to discard clean pages or slab
>> +    /// pages that do not require the starting of any physical IO.
>> +    pub const GFP_NOIO: Flags = Flags(bindings::GFP_NOIO);
>
> How do you use this? What about abstractions for memalloc_noio_{save,restore}()
> instead?

I use it to allocate memory for backing storage in rust null block. The
allocation is done during processing of disk IO:

                page: Page::alloc_page(GFP_NOIO | __GFP_ZERO)?,

Best regards,
Andreas Hindborg