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