Re: [PATCH v2 2/2] fuse: remove tmp folio for writebacks and internal rb tree

[Shakeel Butt <shakeel.butt@linux.dev>]

On Thu, Oct 17, 2024 at 03:31:48PM GMT, Miklos Szeredi wrote:
> On Wed, 16 Oct 2024 at 23:27, Shakeel Butt <shakeel.butt@linux.dev> wrote:
> 
> > Why is it bad? I can understand fuse server getting blocked on fuse
> > folios is bad but why it is bad for other applications/tasks? I am
> > wondering network filesystems have to handle similar situation then why
> > is it bad just for fuse?
> 
> You need privileges (physical access) to unplug the network cable.
> You don't need privileges (in most setups) to run a fuse server.

I feel like this is too much restrictive and I am still not sure why
blocking on fuse folios served by non-privileges fuse server is worse
than blocking on folios served from the network.

> 
> > It might be a bit more than sprinkling. The reclaim code has to activate
> > the folio to avoid reclaiming the folio in near future. I am not sure
> > what we will need to do for move_pages() syscall.
> 
> Maybe move_pages() is okay, because it is explicitly targeting a fuse
> mmap.   Is this the only way to trigger MIGRATE_SYNC?

It can happen through migrate_pages(), mbind(), compaction which can
caused by hugepage allcations.