linux-kernel - Re: Re: Re: [RFC PATCH] fuse: support cache revalidation in writeback

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Date:   Mon, 25 Apr 2022 21:52:44 +0800
From:   Jiachen Zhang <zhangjiachen.jaycee@...edance.com>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xie Yongji <xieyongji@...edance.com>
Subject: Re: Re: Re: [RFC PATCH] fuse: support cache revalidation in
 writeback_cache mode

On Mon, Apr 25, 2022 at 9:42 PM Miklos Szeredi <miklos@...redi.hu> wrote:
>
> On Mon, 25 Apr 2022 at 15:33, Jiachen Zhang
> <zhangjiachen.jaycee@...edance.com> wrote:
> >
> > On Mon, Apr 25, 2022 at 8:41 PM Miklos Szeredi <miklos@...redi.hu> wrote:
> > >
> > > On Fri, 25 Mar 2022 at 14:23, Jiachen Zhang
> > > <zhangjiachen.jaycee@...edance.com> wrote:
> > > >
> > > > Hi all,
> > > >
> > > > This RFC patch implements attr cache and data cache revalidation for
> > > > fuse writeback_cache mode in kernel. Looking forward to any suggestions
> > > > or comments on this feature.
> > >
> > > Quick question before going into the details:  could the cache
> > > revalidation be done in the userspace filesystem instead, which would
> > > set/clear FOPEN_KEEP_CACHE based on the result of the revalidation?
> > >
> > > Thanks,
> > > Miklos
> >
> > Hi, Miklos,
> >
> > Thanks for replying. Yes, I believe we can also perform the
> > revalidation in userspace, and we can invalidate the data cache with
> > FOPEN_KEEP_CACHE cleared. But for now, there is no way we can
> > invalidate attr cache (c/mtime and size)  in writeback mode.
>
> Can you please describe the use case for invalidating the attr cache?
>

Some users may want both the high performance of writeback mode and a
little bit more consistency among FUSE mounts. In the current
writeback mode implementation, users of one FUSE mount can never see
the file expansion done by other FUSE mounts.

Thanks,
Jiachen