Re: [PATCH 3/3] rust: block: convert `block::mq` to use `Refcount`

[Gary Guo]

On Fri, 04 Oct 2024 20:05:41 +0200
Andreas Hindborg <a.hindborg@xxxxxxxxxx> wrote:

> Hi Gary,
> 
> "Gary Guo" <gary@xxxxxxxxxxx> writes:
> 
> > Currently there's a custom reference counting in `block::mq`, which uses
> > `AtomicU64` Rust atomics, and this type doesn't exist on some 32-bit
> > architectures. We cannot just change it to use 32-bit atomics, because
> > doing so will make it vulnerable to refcount overflow. So switch it to
> > use the kernel refcount `kernel::sync::Refcount` instead.
> >
> > There is an operation needed by `block::mq`, atomically decreasing
> > refcount from 2 to 0, which is not available through refcount.h, so
> > I exposed `Refcount::as_atomic` which allows accessing the refcount
> > directly.  
> 
> I would rather wait with this patch until the helper LTO patches land
> upstream. Or at least let me run the benchmarks to see the effect of not
> inlining these refcount operations.
> 
> Best regards,
> Andreas
> 

The helper LTO patch series still need some time. I'd want to be able to
test on 32-bit archs in the meantime.

Best,
Gary