On Tue, Apr 14, 2020 at 05:26:30PM +0200, Jan Kara wrote:
> On Sun 12-04-20 22:40:44, ira.weiny@xxxxxxxxx wrote:
> > From: Ira Weiny <ira.weiny@xxxxxxxxx>
> >
> > DAX effective mode changes (setting of S_DAX) require inode eviction.
> >
> > Define a flag which can be set to inform the VFS layer that inodes
> > should not be cached. This will expedite the eviction of those nodes
> > requiring reload.
> >
> > Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
>
> This inode flag will have a limited impact because usually dentry will
> still hold inode reference. So until dentry is evicted, inode stays as
> well.
Agreed but at least this keeps the inode from being cached until that time.
FWIW the ext4 patches seem to have a much longer delay when issuing drop_caches
and I'm not 100% sure why. I've sent out those patches RFC to get the
discussions started. I feel like I have missed something there but it does
eventually flip the S_DAX flag.
> So I think we'd need something like DCACHE_DONTCACHE flag as well to
> discard a dentry whenever dentry usecount hits zero (which will be
> generally on last file close). What do you think?
I wanted to do something like this but I was not sure how to trigger the
DCACHE_DONTCACHE on the correct 'parent' dentry. Can't their be multiple
dentries pointing to the same inode?
In which case, would you need to flag them all?
Ira
>
> And I'd note that checking for I_DONTCACHE flag in dput() isn't
> straightforward because of locking so that's why I suggest separate dentry
> flag.
>
> Honza
>
> > ---
> > include/linux/fs.h | 6 +++++-
> > 1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index a818ced22961..e2db71d150c3 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -2151,6 +2151,8 @@ static inline void kiocb_clone(struct kiocb *kiocb, struct kiocb *kiocb_src,
> > *
> > * I_CREATING New object's inode in the middle of setting up.
> > *
> > + * I_DONTCACHE Do not cache the inode
> > + *
> > * Q: What is the difference between I_WILL_FREE and I_FREEING?
> > */
> > #define I_DIRTY_SYNC (1 << 0)
> > @@ -2173,6 +2175,7 @@ static inline void kiocb_clone(struct kiocb *kiocb, struct kiocb *kiocb_src,
> > #define I_WB_SWITCH (1 << 13)
> > #define I_OVL_INUSE (1 << 14)
> > #define I_CREATING (1 << 15)
> > +#define I_DONTCACHE (1 << 16)
> >
> > #define I_DIRTY_INODE (I_DIRTY_SYNC | I_DIRTY_DATASYNC)
> > #define I_DIRTY (I_DIRTY_INODE | I_DIRTY_PAGES)
> > @@ -3042,7 +3045,8 @@ extern int inode_needs_sync(struct inode *inode);
> > extern int generic_delete_inode(struct inode *inode);
> > static inline int generic_drop_inode(struct inode *inode)
> > {
> > - return !inode->i_nlink || inode_unhashed(inode);
> > + return !inode->i_nlink || inode_unhashed(inode) ||
> > + (inode->i_state & I_DONTCACHE);
> > }
> >
> > extern struct inode *ilookup5_nowait(struct super_block *sb,
> > --
> > 2.25.1
> >
> --
> Jan Kara <jack@xxxxxxxx>
> SUSE Labs, CR
