On Tue, Nov 4, 2014 at 11:55 AM, Jan Kara <jack@xxxxxxx> wrote: > 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? > Yeah, this idea clearly doesn't work. But I wonder whether the revised variant (which may be just moving cd_forget and bd_forget from evict to iput_final) would work. --Andy > Honza > -- > Jan Kara <jack@xxxxxxx> > SUSE Labs, CR -- Andy Lutomirski AMA Capital Management, LLC -- 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
