On Tue 04-11-14 11:47:21, Andy Lutomirski 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.) I can see a few reasons: 1) positive dentry without inode - no-no for dcache. 2) how would you get the information which device the dentry references? 3) what would you gain to outweight the complications and special code paths? Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- 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
