On Thu, Aug 01, 2013 at 01:12:35AM -0700, Christoph Hellwig wrote: > On Wed, Jul 31, 2013 at 02:15:41PM +1000, Dave Chinner wrote: > > From: Dave Chinner <dchinner@xxxxxxxxxx> > > > > Some filesystems don't use the VFS inode hash and fake the fact they > > are hashed so that all the writeback code works correctly. However, > > this means the evict() path still tries to remove the inode from the > > hash, meaning that the inode_hash_lock() needs to be taken > > unnecessarily. Hence under certain workloads the inode_hash_lock can > > be contended even if the inode is never actually hashed. > > > > To avoid this, add an inode opflag to allow inode_hash_remove() to > > avoid taking the hash lock on inodes have never actually been > > hashed. > > Good idea, but I don't like how it's implemented. > > First a formality: i_opflags really is for flags showing that inode > operations exist, not for addional bits. Just use i_flags for it. > > Second this is a hack hacking around a hack. We just mark the inode > hashed so that writeback doesn't ignore it, and not we need to work > around the fact that we don't want an inode marked hashed from the > hashlist. > > As the most simple version I'd suggest to just add an I_NEEDS_WRITEBACK > flag which gets set by __insert_inode_hash, and all the current users > of hlist_add_fake on i_hash, as well as the block devices that currently > have another special case in the writeback code. But that doesn't fix the problem of taking the hash lock in evict() when it is not necessary. If everything sets I_NEEDS_WRITEBACK, and we still fake hashing the inode, how are do we know that we don't need to unhash it in evict()? Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
