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Date: Sun, 25 Jun 2023 21:39:27 +0100
From: Gary Guo <gary@...yguo.net>
To: Boqun Feng <boqun.feng@...il.com>
Cc: bjorn3_gh@...tonmail.com, Miguel Ojeda <ojeda@...nel.org>,
Alex Gaynor <alex.gaynor@...il.com>,
Wedson Almeida Filho <wedsonaf@...il.com>,
Benno Lossin <benno.lossin@...ton.me>,
rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rust: alloc: Add realloc and alloc_zeroed to the
GlobalAlloc impl
On Fri, 23 Jun 2023 10:35:00 -0700
Boqun Feng <boqun.feng@...il.com> wrote:
> On Thu, Jun 22, 2023 at 09:24:40PM +0200, Björn Roy Baron via B4 Relay wrote:
> > From: Björn Roy Baron <bjorn3_gh@...tonmail.com>
> >
> > While there are default impls for these methods, using the respective C
> > api's is faster. Currently neither the existing nor these new
> > GlobalAlloc method implementations are actually called. Instead the
> > __rust_* function defined below the GlobalAlloc impl are used. With
> > rustc 1.71 these functions will be gone and all allocation calls will go
> > through the GlobalAlloc implementation.
> >
> > Link: https://github.com/Rust-for-Linux/linux/issues/68
>
> Nice! Although I think we need to do the simialr size adjustment as:
>
> https://lore.kernel.org/rust-for-linux/20230613164258.3831917-1-boqun.feng@gmail.com/
>
> so I applied your patch onto my patch and came up with the following:
The diff LGTM.
>
> --------------------------------->8
> diff --git a/rust/kernel/allocator.rs b/rust/kernel/allocator.rs
> index ce7a06bf7589..af723c2924dc 100644
> --- a/rust/kernel/allocator.rs
> +++ b/rust/kernel/allocator.rs
> @@ -9,8 +9,17 @@
>
> struct KernelAllocator;
>
> -unsafe impl GlobalAlloc for KernelAllocator {
> - unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
> +impl KernelAllocator {
> + /// # Safety
> + ///
> + /// * `ptr` can be either null or a pointer which has been allocated by this allocator.
> + /// * `layout` must have a non-zero size.
> + unsafe fn krealloc_with_flags(
> + &self,
> + ptr: *mut u8,
> + layout: Layout,
> + flags: bindings::gfp_t,
> + ) -> *mut u8 {
> // Customized layouts from `Layout::from_size_align()` can have size < align, so pads first.
> let layout = layout.pad_to_align();
>
> @@ -26,9 +35,22 @@ unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
> size = size.next_power_of_two();
> }
>
> - // `krealloc()` is used instead of `kmalloc()` because the latter is
> - // an inline function and cannot be bound to as a result.
> - unsafe { bindings::krealloc(ptr::null(), size, bindings::GFP_KERNEL) as *mut u8 }
> + // SAFETY:
> + //
> + // * `ptr` is either null or a pointer returned from a previous k{re}alloc() by the function
> + // safety requirement.
> + //
> + // * `size` is greater than 0 since it's either a `layout.size()` (which cannot be zero
> + // according to the function safety requirement) or a result from `next_power_of_two()`.
> + unsafe { bindings::krealloc(ptr as *const core::ffi::c_void, size, flags) as *mut u8 }
> + }
> +}
> +
> +unsafe impl GlobalAlloc for KernelAllocator {
> + unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
> + // SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
> + // requirement.
> + unsafe { self.krealloc_with_flags(ptr::null_mut(), layout, bindings::GFP_KERNEL) }
> }
>
> unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
> @@ -37,23 +59,30 @@ unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
> }
> }
>
> - unsafe fn realloc(&self, ptr: *mut u8, _layout: Layout, new_size: usize) -> *mut u8 {
> - unsafe {
> - bindings::krealloc(
> - ptr as *const core::ffi::c_void,
> - new_size,
> - bindings::GFP_KERNEL,
> - ) as *mut u8
> - }
> + unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
> + // SAFETY:
> + // * `new_size` when rounded up to the nearest multiple of `layout.align()`, will not
> + // overflow `isize` by the function safety requirement.
> + // * `layout.align()` is a proper alignment (i.e. not zero and must be a power of two).
> + let layout = unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
> +
> + // SAFETY:
> + // * `ptr` is either null or a pointer allocated by this allocator by function safety
> + // requirement.
> + // * the size of `layout` is not zero because `new_size` is not zero by function safety
> + // requirement.
> + unsafe { self.krealloc_with_flags(ptr, layout, bindings::GFP_KERNEL) }
> }
>
> unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
> + // SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
> + // requirement.
> unsafe {
> - bindings::krealloc(
> - core::ptr::null(),
> - layout.size(),
> + self.krealloc_with_flags(
> + ptr::null_mut(),
> + layout,
> bindings::GFP_KERNEL | bindings::__GFP_ZERO,
> - ) as *mut u8
> + )
> }
> }
> }
>
>
> Regards,
> Boqun
>
> > Signed-off-by: Björn Roy Baron <bjorn3_gh@...tonmail.com>
> > ---
> > rust/kernel/allocator.rs | 20 ++++++++++++++++++++
> > 1 file changed, 20 insertions(+)
> >
> > diff --git a/rust/kernel/allocator.rs b/rust/kernel/allocator.rs
> > index 397a3dd57a9b..e0a27b1326b5 100644
> > --- a/rust/kernel/allocator.rs
> > +++ b/rust/kernel/allocator.rs
> > @@ -21,6 +21,26 @@ unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
> > bindings::kfree(ptr as *const core::ffi::c_void);
> > }
> > }
> > +
> > + unsafe fn realloc(&self, ptr: *mut u8, _layout: Layout, new_size: usize) -> *mut u8 {
> > + unsafe {
> > + bindings::krealloc(
> > + ptr as *const core::ffi::c_void,
> > + new_size,
> > + bindings::GFP_KERNEL,
> > + ) as *mut u8
> > + }
> > + }
> > +
> > + unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
> > + unsafe {
> > + bindings::krealloc(
> > + core::ptr::null(),
> > + layout.size(),
> > + bindings::GFP_KERNEL | bindings::__GFP_ZERO,
> > + ) as *mut u8
> > + }
> > + }
> > }
> >
> > #[global_allocator]
> >
> > ---
> > base-commit: d2e3115d717197cb2bc020dd1f06b06538474ac3
> > change-id: 20230622-global_alloc_methods-abf5b5e38dba
> >
> > Best regards,
> > --
> > Björn Roy Baron <bjorn3_gh@...tonmail.com>
> >
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