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Message-ID: <ZrJzJyj7kej0hA0p@pollux.localdomain>
Date: Tue, 6 Aug 2024 21:01:59 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: ojeda@...nel.org, alex.gaynor@...il.com, wedsonaf@...il.com,
boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com,
a.hindborg@...sung.com, aliceryhl@...gle.com,
akpm@...ux-foundation.org, daniel.almeida@...labora.com,
faith.ekstrand@...labora.com, boris.brezillon@...labora.com,
lina@...hilina.net, mcanal@...lia.com, zhiw@...dia.com,
acurrid@...dia.com, cjia@...dia.com, jhubbard@...dia.com,
airlied@...hat.com, ajanulgu@...hat.com, lyude@...hat.com,
linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [PATCH v4 06/28] rust: alloc: implement `Vmalloc` allocator
On Tue, Aug 06, 2024 at 05:00:24PM +0000, Benno Lossin wrote:
> On 05.08.24 17:19, Danilo Krummrich wrote:
> > Implement `Allocator` for `Vmalloc`, the kernel's virtually contiguous
> > allocator, typically used for larger objects, (much) larger than page
> > size.
> >
> > All memory allocations made with `Vmalloc` end up in `vrealloc()`.
> >
> > Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
> > Signed-off-by: Danilo Krummrich <dakr@...nel.org>
> > ---
> > rust/helpers.c | 7 +++++++
> > rust/kernel/alloc/allocator.rs | 32 +++++++++++++++++++++++++++++
> > rust/kernel/alloc/allocator_test.rs | 1 +
> > 3 files changed, 40 insertions(+)
> >
> > diff --git a/rust/helpers.c b/rust/helpers.c
> > index 9f7275493365..7406943f887d 100644
> > --- a/rust/helpers.c
> > +++ b/rust/helpers.c
> > @@ -33,6 +33,7 @@
> > #include <linux/sched/signal.h>
> > #include <linux/slab.h>
> > #include <linux/spinlock.h>
> > +#include <linux/vmalloc.h>
> > #include <linux/wait.h>
> > #include <linux/workqueue.h>
> >
> > @@ -199,6 +200,12 @@ void *rust_helper_krealloc(const void *objp, size_t new_size, gfp_t flags)
> > }
> > EXPORT_SYMBOL_GPL(rust_helper_krealloc);
> >
> > +void *rust_helper_vrealloc(const void *p, size_t size, gfp_t flags)
> > +{
> > + return vrealloc(p, size, flags);
> > +}
> > +EXPORT_SYMBOL_GPL(rust_helper_vrealloc);
> > +
> > /*
> > * `bindgen` binds the C `size_t` type as the Rust `usize` type, so we can
> > * use it in contexts where Rust expects a `usize` like slice (array) indices.
> > diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
> > index c6ad1dd59dd0..bb55895cbd03 100644
> > --- a/rust/kernel/alloc/allocator.rs
> > +++ b/rust/kernel/alloc/allocator.rs
> > @@ -9,6 +9,7 @@
> >
> > use crate::alloc::{AllocError, Allocator};
> > use crate::bindings;
> > +use crate::pr_warn;
> >
> > /// The contiguous kernel allocator.
> > ///
> > @@ -16,6 +17,12 @@
> > /// `bindings::krealloc`.
> > pub struct Kmalloc;
> >
> > +/// The virtually contiguous kernel allocator.
> > +///
> > +/// The vmalloc allocator allocates pages from the page level allocator and maps them into the
> > +/// contiguous kernel virtual space.
> > +pub struct Vmalloc;
>
> One thing that I should also have mentioned for `Kmalloc`, do we want
> these types to also have values? I don't think that we need them to be,
> so we could declare them as `pub enum Vmalloc {}`.
What the difference? Would `pub enum Vmalloc {}` be better for some reason?
>
> > +
> > /// Returns a proper size to alloc a new object aligned to `new_layout`'s alignment.
> > fn aligned_size(new_layout: Layout) -> usize {
> > // Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
> > @@ -61,6 +68,11 @@ fn krealloc() -> Self {
> > Self(bindings::krealloc)
> > }
> >
> > + // INVARIANT: `vrealloc` satisfies the type invariants.
>
> This should be moved down a line.
>
> ---
> Cheers,
> Benno
>
> > + fn vrealloc() -> Self {
> > + Self(bindings::vrealloc)
> > + }
> > +
> > /// # Safety
> > ///
> > /// This method has the exact same safety requirements as `Allocator::realloc`.
> > @@ -141,6 +153,26 @@ unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
> > }
> > }
> >
> > +unsafe impl Allocator for Vmalloc {
> > + unsafe fn realloc(
> > + ptr: Option<NonNull<u8>>,
> > + layout: Layout,
> > + flags: Flags,
> > + ) -> Result<NonNull<[u8]>, AllocError> {
> > + let realloc = ReallocFunc::vrealloc();
> > +
> > + // TODO: Support alignments larger than PAGE_SIZE.
> > + if layout.align() > bindings::PAGE_SIZE {
> > + pr_warn!("Vmalloc does not support alignments larger than PAGE_SIZE yet.\n");
> > + return Err(AllocError);
> > + }
> > +
> > + // SAFETY: If not `None`, `ptr` is guaranteed to point to valid memory, which was previously
> > + // allocated with this `Allocator`.
> > + unsafe { realloc.call(ptr, layout, flags) }
>
> I am a bit confused, for `Kmalloc`, you manually returned
> `NonNull::dangling` when allocating a zero-sized allocation, but here
> you don't?
>
I do, it's the exact same implementation for krealloc(), vrealloc() and
kvrealloc(). That why I added the `ReallocFunc` abstraction.
> ---
> Cheers,
> Benno
>
> > + }
> > +}
> > +
> > #[global_allocator]
> > static ALLOCATOR: Kmalloc = Kmalloc;
> >
> > diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs
> > index 4785efc474a7..e7bf2982f68f 100644
> > --- a/rust/kernel/alloc/allocator_test.rs
> > +++ b/rust/kernel/alloc/allocator_test.rs
> > @@ -7,6 +7,7 @@
> > use core::ptr::NonNull;
> >
> > pub struct Kmalloc;
> > +pub type Vmalloc = Kmalloc;
> >
> > unsafe impl Allocator for Kmalloc {
> > unsafe fn realloc(
> > --
> > 2.45.2
> >
>
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