Messages in this thread | | | Date | Tue, 23 Feb 2016 14:01:55 -0500 | From | Waiman Long <> | Subject | Re: [PATCH v2 3/3] vfs: Use per-cpu list for superblock's inode list |
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On 02/22/2016 08:04 AM, Jan Kara wrote: > On Mon 22-02-16 13:12:22, Peter Zijlstra wrote: >> On Mon, Feb 22, 2016 at 12:54:35PM +0100, Jan Kara wrote: >>>> Also, I think fsnotify_unmount_inodes() (as per mainline) is missing a >>>> final iput(need_iput) at the very end, but I could be mistaken, that >>>> code hurts my brain. >>> I think the code is actually correct since need_iput contains "inode >>> further in the list than the current inode". Thus we will always go though >>> another iteration of the loop which will drop the reference. And inode >>> cannot change state to I_FREEING or I_WILL_FREE because we hold inode >>> reference. But it is subtle as hell so I agree that code needs rewrite. >> So while talking to dchinner, he doubted fsnotify will actually remove >> inodes from the sb-list, but wasn't sure and too tired to check now. >> >> (I got lost in the fsnotify code real quick and gave up, for I was >> mostly trying to make a point that we don't need the CPP magic and can >> do with 'readable' code). >> >> If it doesn't, it doesn't need to do this extra special magic dance and >> can use the 'normal' iterator pattern used in all the other functions, >> greatly reducing complexity. > Yeah, that would be nice. But fsnotify code needs to iterate over all > inodes, drop sb_list_lock and do some fsnotify magic with the inode which > is not substantial for our discussion. Now that fsnotify magic may actually > drop all the remaining inode references so once we drop our reference > pinning the inode, it can just disappear. We don't want to restart the scan > for each inode we have to process so that is the reason why we play ugly > tricks with pinning the next inode in the list. > > But I agree it should be possible to just use list_for_each_entry() instead > of list_for_each_entry_safe() and keep current inode pinned till the next > iteration to make it stick in the sb->s_inodes list. That would make the > iteration more standard. Lightly tested patch attached. > > Honza
Your patch looks good to me. I would like to put your patch into my per-cpu list patchset if you don't mind.
Cheers, Longman
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