On Mon, Jun 27, 2022 at 10:45 PM Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
>
> On Tue, Apr 26, 2022 at 03:09:05PM +0200, Miklos Szeredi wrote:
> > On Mon, Apr 25, 2022 at 09:52:44PM +0800, Jiachen Zhang wrote:
> >
> > > 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.
> >
> > Okay.
> >
> > Here's a preliminary patch that you could try.
> >
> > Thanks,
> > Miklos
> >
> > ---
> > fs/fuse/dir.c | 35 ++++++++++++++++++++++-------------
> > fs/fuse/file.c | 17 +++++++++++++++--
> > fs/fuse/fuse_i.h | 14 +++++++++++++-
> > fs/fuse/inode.c | 32 +++++++++++++++++++++++++++-----
> > include/uapi/linux/fuse.h | 5 +++++
> > 5 files changed, 82 insertions(+), 21 deletions(-)
> >
> > --- a/include/uapi/linux/fuse.h
> > +++ b/include/uapi/linux/fuse.h
> > @@ -194,6 +194,7 @@
> > * - add FUSE_SECURITY_CTX init flag
> > * - add security context to create, mkdir, symlink, and mknod requests
> > * - add FUSE_HAS_INODE_DAX, FUSE_ATTR_DAX
> > + * - add FUSE_WRITEBACK_CACHE_V2 init flag
> > */
> >
> > #ifndef _LINUX_FUSE_H
> > @@ -353,6 +354,9 @@ struct fuse_file_lock {
> > * FUSE_SECURITY_CTX: add security context to create, mkdir, symlink, and
> > * mknod
> > * FUSE_HAS_INODE_DAX: use per inode DAX
> > + * FUSE_WRITEBACK_CACHE_V2:
> > + * - allow time/size to be refreshed if no pending write
> > + * - time/size not cached for falocate/copy_file_range
> > */
> > #define FUSE_ASYNC_READ (1 << 0)
> > #define FUSE_POSIX_LOCKS (1 << 1)
> > @@ -389,6 +393,7 @@ struct fuse_file_lock {
> > /* bits 32..63 get shifted down 32 bits into the flags2 field */
> > #define FUSE_SECURITY_CTX (1ULL << 32)
> > #define FUSE_HAS_INODE_DAX (1ULL << 33)
> > +#define FUSE_WRITEBACK_CACHE_V2 (1ULL << 34)
> >
> > /**
> > * CUSE INIT request/reply flags
> > --- a/fs/fuse/inode.c
> > +++ b/fs/fuse/inode.c
> > @@ -222,19 +222,37 @@ void fuse_change_attributes_common(struc
> > u32 fuse_get_cache_mask(struct inode *inode)
> > {
> > struct fuse_conn *fc = get_fuse_conn(inode);
> > + struct fuse_inode *fi = get_fuse_inode(inode);
> >
> > if (!fc->writeback_cache || !S_ISREG(inode->i_mode))
> > return 0;
> >
> > + /*
> > + * In writeback_cache_v2 mode if all the following conditions are met,
> > + * then allow the attributes to be refreshed:
> > + *
> > + * - inode is not dirty (I_DIRTY_INODE)
> > + * - inode is not in the process of being written (I_SYNC)
> > + * - inode has no dirty pages (I_DIRTY_PAGES)
> > + * - inode does not have any page writeback in progress
> > + *
> > + * Note: checking PAGECACHE_TAG_WRITEBACK is not sufficient in fuse,
> > + * since inode can appear to have no PageWriteback pages, yet still have
> > + * outstanding write request.
> > + */
>
> Hi,
>
> I started following this thread just now after Jiachen pointed me to
> previous conversations. Without going into too much details.
>
> Based on above description, so we will update mtime/ctime/i_size only
> if inode does not have dirty pages or nothing is in progress. So that
> means sometime we will update it and other times we will ignore it.
>
> Do I understand it correctly. I am wondering how that is useful to
> applications.
>
> I thought that other remote filesystems might have leasing for this so
> that one client can acquire the lease and cache changes and when lease
> is broken, this client pushes out all the changes and other client gets
> the lease.
>
> Given we don't have any lease mechanism, we probably need to define the
> semantics more clearly and we should probably document it as well.
>
Hi Vivek,
I agree we should define or document the semantics properly. For now,
it seems that Miklos' writeback_mode_v2 is making best-effort updating
when pages are not dirty and a set of new attributes are returned from
FUSE server.
Thanks,
Jiachen
> Thanks
> Vivek
>
