On Fri, Aug 21, 2020 at 10:40:41AM -0700, 'Ira Weiny' wrote: > On Fri, Aug 21, 2020 at 09:59:53AM +0800, Hao Li wrote: > > Currently, DCACHE_REFERENCED prevents the dentry with DCACHE_DONTCACHE > > set from being killed, so the corresponding inode can't be evicted. If > > the DAX policy of an inode is changed, we can't make policy changing > > take effects unless dropping caches manually. > > > > This patch fixes this problem and flushes the inode to disk to prepare > > for evicting it. > > This looks intriguing and I really hope this helps but I don't think this will > guarantee that the state changes immediately will it? > > Do you have a test case which fails before and passes after? Perhaps one of > the new xfstests submitted by Xiao? Ok I just went back and read your comment before.[1] Sorry for being a bit slow on the correlation between this patch and that email. (BTW, I think it would have been good to put those examples in the commit message and or reference that example.) I'm assuming that with this patch example 2 from [1] works without a drop_cache _if_ no other task has the file open? Anyway, with that explanation I think you are correct that this improves the situation _if_ the only references on the file is controlled by the user and they have indeed closed all of them. The code for DCACHE_DONTCACHE as I attempted to write it was that it should have prevented further caching of the inode such that the inode would evict sooner. But it seems you have found a bug/optimization? In the end, however, if another user (such as a backup running by the admin) has a reference the DAX change may still be delayed. So I'm thinking the documentation should remain largely as is? But perhaps I am wrong. Does this completely remove the need for a drop_caches or only in the example you gave? Since I'm not a FS expert I'm still not sure. Regardless, thanks for the fixup! :-D Ira [1] https://lore.kernel.org/linux-xfs/ba98b77e-a806-048a-a0dc-ca585677daf3@xxxxxxxxxxxxxx/ > > Ira > > > > > Signed-off-by: Hao Li <lihao2018.fnst@xxxxxxxxxxxxxx> > > --- > > fs/dcache.c | 3 ++- > > fs/inode.c | 2 +- > > 2 files changed, 3 insertions(+), 2 deletions(-) > > > > diff --git a/fs/dcache.c b/fs/dcache.c > > index ea0485861d93..486c7409dc82 100644 > > --- a/fs/dcache.c > > +++ b/fs/dcache.c > > @@ -796,7 +796,8 @@ static inline bool fast_dput(struct dentry *dentry) > > */ > > smp_rmb(); > > d_flags = READ_ONCE(dentry->d_flags); > > - d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED; > > + d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED > > + | DCACHE_DONTCACHE; > > > > /* Nothing to do? Dropping the reference was all we needed? */ > > if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry)) > > diff --git a/fs/inode.c b/fs/inode.c > > index 72c4c347afb7..5218a8aebd7f 100644 > > --- a/fs/inode.c > > +++ b/fs/inode.c > > @@ -1632,7 +1632,7 @@ static void iput_final(struct inode *inode) > > } > > > > state = inode->i_state; > > - if (!drop) { > > + if (!drop || (drop && (inode->i_state & I_DONTCACHE))) { > > WRITE_ONCE(inode->i_state, state | I_WILL_FREE); > > spin_unlock(&inode->i_lock); > > > > -- > > 2.28.0 > > > > > >
