On Wed, Jun 10, 2009 at 04:08:39PM +0100, Al Viro wrote: > We can, but... it's again a matter of combining things with different > locking. i_flags is protected by i_mutex, so if you put another > unsigned short next to it, you'd better make sure that i_mutex > is necessary and sufficient for modifying it. > > Depending on the target, gcc may turn 16bit read-modify-store into 32bit one, > so if you have two 16bit fields next to each other, you can run into > > CPU1: CPU2: > r1 = *(u32 *)p; r2 = *(u32 *)p; > r1 |= 1; r2 |= 1 << 16; > *(u32 *)p = r1; *(u32 *)p = r2; > > with obvious results. So we need the same locking for both such fields... Yelch.... good point. I'll look and see if there's some other 8 or 16-bit type to combine it with, but we may have started to hit diminishing returns with this this approach to sliming the inode slab caches. I'm beginning to think if I want to make the inodes smaller, I'm going to have to create a separate substructure for fields only used when a file descriptor is opened on that inode, both in struct inode and in struct ext4_inode_info. (Lifetime management of the substructure is going to be non-trivial, though.) - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
