linux-ext4 - Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it

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Message-ID: <871st519vf.fsf@notabene.neil.brown.name>
Date:   Fri, 07 Apr 2017 07:53:08 +1000
From:   NeilBrown <neilb@...e.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Jeff Layton <jlayton@...hat.com>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org,
        akpm@...ux-foundation.org, tytso@....edu, jack@...e.cz
Subject: Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it

On Thu, Apr 06 2017, Matthew Wilcox wrote:

> On Thu, Apr 06, 2017 at 03:12:42PM +1000, NeilBrown wrote:
>> On Wed, Apr 05 2017, Matthew Wilcox wrote:
>> 
>> > On Thu, Apr 06, 2017 at 10:02:48AM +1000, NeilBrown wrote:
>> >> If you are concerned about space in 'struct address_space', just prune
>> >> some wastage.
>> >
>> > I'm trying to (via wlists).  still buggy though.
>> 
>> Cool.
>> (I wonder what a wlist is.... weighted list?)
>
> A homonym ;-)  Waitlists.  Yet Another Variation of a doubly linked list.
> This variation has only a single head pointer (like the hlist), allows
> O(1) deletion from any point in the list (but requires that you know the
> head of the list).  The tail of the list is pointed to by head->prev.
>
> http://git.infradead.org/users/willy/linux-dax.git/shortlog/refs/heads/wlist
>
> It also needs updating to the latest tree; WW locks got revamped.

So nothing points to the head, meaning you need both the node and the
head to delete something.  But the head is smaller.
I can see how that would be useful.
Thanks,
NeilBrown

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