Re: [PATCH 2/2] rust_binder: charge allocated pages to memcg

[T.J. Mercier]

On Fri, Oct 16, 2026 at 6:30 AM Alice Ryhl <aliceryhl@xxxxxxxxxx> wrote:
>
> Pages allocated for a binder VMA are currently not charged to any memory
> cgroup. Thus, use `Page::alloc_page_memcg()` to charge them to the
> owning process's `mm_struct`.
>
> Suggested-by: T.J. Mercier <tjmercier@xxxxxxxxxx>
> Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> ---
>  drivers/android/binder/page_range.rs | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/android/binder/page_range.rs b/drivers/android/binder/page_range.rs
> index 52ffbf3504e7..57da47243967 100644
> --- a/drivers/android/binder/page_range.rs
> +++ b/drivers/android/binder/page_range.rs
> @@ -27,7 +27,7 @@
>      ffi::{c_ulong, c_void},
>      mm::{virt, Mm, MmWithUser},
>      new_mutex, new_spinlock,
> -    page::{Page, PAGE_SHIFT, PAGE_SIZE},
> +    page::{MemcgAllocError, Page, PAGE_SHIFT, PAGE_SIZE},
>      prelude::*,
>      str::CStr,
>      sync::{aref::ARef, Mutex, SpinLock},
> @@ -399,7 +399,16 @@ pub(crate) fn use_range(&self, start: usize, end: usize) -> Result<()> {
>      /// Assumes that `i` is in bounds.
>      #[cold]
>      unsafe fn use_page_slow(&self, i: usize) -> Result<()> {
> -        let new_page = Page::alloc_page(GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO)?;
> +        let new_page = Page::alloc_page_memcg(GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO, &self.mm)

Not related to this change, but I think it might be better to ditch
GFP_KERNEL | __GFP_HIGHMEM and use GFP_HIGHUSER. We're already mapping
this into userspace (and now charging the memcg for it).

Is current the sender here? If memory.high is exceeded, current gets
blamed for it in try_charge_memcg()'s done_restock section. So if it's
the sender, that's not exactly what we want since the sender would be
throttled for it. So I think this depends on
https://lore.kernel.org/all/20261010210957.1350874-4-shakeel.butt@xxxxxxxxx/.



> +            .inspect_err(|err| {
> +                if *err == MemcgAllocError::Memcg {
> +                    binder_debug!(
> +                        FailedTransaction,
> +                        "page allocation for message to {} was blocked by memory cgroup limits",
> +                        self.pid,
> +                    );
> +                }
> +            })?;
>
>          let mm_mutex = self.mm_lock.lock();
>          let inner = self.lock.lock();
>
> --
> 2.56.0.212.g129ede20d9-goog
>