On Tue, 2010-10-26 at 10:22 +1100, Dave Chinner wrote: > On Mon, Oct 25, 2010 at 02:41:18PM -0400, Eric Paris wrote: > > The IMA code needs to store the number of tasks which have an open fd > > granting permission to write a file even when IMA is not in use. It needs > > this information in order to be enabled at a later point in time without > > losing it's integrity garantees. At the moment that means we store a > > little bit of data about every inode in a cache. We use a radix tree key'd > > on the inode's memory address. Dave Chinner pointed out that a radix tree > > is a terrible data structure for such a sparse key space. This patch > > switches to using an rbtree which should be more efficient. > > I'm not sure this is the right fix, though. > > Realistically, there is a 1:1 relationship between the inode and the > IMA information. I fail to see why an external index is needed here > at all - just use a separate structure to store the IMA information > that the inode points to. That makes the need for a new global index > and global lock go away completely. I guess I did a bad job explaining my 1:1 relationship comments. I only need the i_readcount in a 1:1 manor. (I'm also using the already existing i_writecount) So IMA needs some information in a 1:1 relationship, but everything else in the IMA structure is only needed when 'a measurement policy is loaded.' I believe that IBM is going to look into making i_readcount a first class citizen which can be used by both IMA and generic_setlease(). Then people could say IMA had 0 per inode overhead :) > You're already adding 8 bytes to the inode, so why not make it a > pointer. 4 + 4 padding. Yes. > We've got 4 conditions: You're suggesting we go to 4 conditions? Today we have 3. > 1. not configured - no overhead > 2. configured, boot time disabled - 8 bytes per inode > 3. configured, boot time enabled, runtime disabled - 8 bytes per > inode + small IMA structure 2 and 3 are the same today, and both are 4+4. I believe your suggestion would be for #3 would be 8 bytes in inode pointing to a 4+4 byte structure. I don't really know if that gets us anything. > 4. configured, boot time enabled, runtime enabled - 8 bytes per > inode + large IMA structure > Anyone who wants the option of runtime enablement can take the extra > allocation overhead, but otherwise nobody is affected apart from 8 > bytes of additional memory per inode. I doubt that will change > anything unless it increases the size of the inode enough to push it > over slab boundaries. And if LSM stacking is introduced, then that 8 > bytes per inode overhead will go away, anyway. At least it gets shifted so you don't see it. Can't say it goes away.... > This approach doesn't introduce new global lock and lookup overhead > into the main VFS paths, allows you to remove a bunch of code and > has a path forward for removing the 8 byte per inode overhead as > well. Seems like the best compromise to me.... End of my patch series there are no global locks in main VFS paths (unless you load an ima measurement policy). I realize that this patch switches an rcu_readlock() to a spin_lock() and maybe that's what you means, but you'll find that I drop ALL locking on core paths when you don't load a measurement policy in 10/11 http://marc.info/?l=linux-kernel&m=128803236419823&w=2 -Eric -- 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
