Re: [PATCH v3 0/7] assorted ->i_count changes + extension of lockless handling

[Mateusz Guzik]

On Tue, Mar 31, 2026 at 1:32 PM Christian Brauner <brauner@xxxxxxxxxx> wrote:
>
> On Sun, Mar 29, 2026 at 07:19:55PM +0200, Mateusz Guzik wrote:
> > The stock kernel support partial lockless in handling in that iput() can
> > decrement any value > 1. Any ref acquire however requires the spinlock.
> >
> > With this patchset ref acquires when the value was already at least 1
> > also become lockless. That is, only transitions 0->1 and 1->0 take the
> > lock.
> >
> > I verified when nfs calls into the hash taking the lock is typically
> > avoided. Similarly, btrfs likes to igrab() and avoids the lock.
> > However, I have to fully admit I did not perform any benchmarks. While
> > cleaning stuff up I noticed lockless operation is almost readily
> > available so I went for it.
> >
> > Clean-up wise, the icount_read_once() stuff lines up with inode_state_read_once().
> > The prefix is different but I opted to not change it due to igrab(), ihold() et al.
> >
> > There is a future-proofing change in iput_final(). I am not going to
> > strongly insist on it, but at the very least the problem needs to be
> > noted in a comment.
>
> Seems overall good to me aside from the bdev_file_open_by_dev() splat
> ofc.

The splat is fixed in v4
https://lore.kernel.org/linux-fsdevel/20260330122602.3659417-1-mjguzik@xxxxxxxxx/T/#m93beb6028303f113d5d902120db834d54d52cf97