On Tue, Nov 4, 2014 at 11:47 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > On 11/04/2014 07:39 AM, Al Viro wrote: >> On Tue, Nov 04, 2014 at 11:27:27AM +0100, Jan Kara wrote: >>> Hello, >>> >>> this patch set removes use of i_devices from block and character device >>> code and thus we can remove the list head from struct inode thus saving two >>> pointers in it. As Christoph has reviewed the series, can you please merge >>> it Al? Thanks! >>> >>> Since v2 I've added reviewed-by tags from Christoph and changed one variable >>> name in cdev_forget(). >>> >>> Since v1 I have split the patches and properly handled character devices (I >>> broke them last time as Christoph pointed out). >> >> My problem with that is in buggered module refcounts (which was the reason >> for doing those non-counting references back then). Suppose you open >> /dev/some_char_device and close it; having the module pinned down until >> the inode of that sucker gets evicted by dcache/icache memory pressure >> would be wrong - it _isn't_ in use, and there's no way short of forcing >> the full eviction of VFS caches to get it possible to unload... >> > > At the risk of asking what may be a rather dumb question... > > Why do device node inodes need to be cached at all? In other words, > when you try open a device node, can't the kernel materialize the inode > from just information that's in the dentry without touching the > filesystem at all? If that's true, couldn't all device inodes be > dropped from icache as soon as they're unreferenced? > > (Yes, there's mtime, but I never understood why tracking mtime on device > nodes made any sense in the first place.) On further reflection, this is indeed a dumb question. i_rdev is in the inode, so of course the inode is useful. Let me try again, though: what if a chardev inode replaced i_cdev with NULL and dropped its kobj reference in iput_final? This would add a bit over overhead to things that repeatedly open and close the same device node, but I doubt this matters much. --Andy -- 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
