linux-kernel - Re: [PATCH 2/3] Improve fairness when locking the per-superblock s

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Message-ID: <20171110085035.GA2304@infradead.org>
Date:   Fri, 10 Nov 2017 00:50:35 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     NeilBrown <neilb@...e.com>, Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] Improve fairness when locking the per-superblock
 s_anon list

On Thu, Nov 09, 2017 at 11:52:48AM -0800, Linus Torvalds wrote:
> Yes, getting rid of s_anon might involve crazy things like "let's just
> walk all the dentries at umount time", but honestly, that sounds
> preferable. Especially if we can just then do something like
> 
>  - set a special flag in the superblock if we ever use __d_obtain_alias()
> 
>  - only scan all the dentries on umount if that flag is set.
> 
> Hmm?

The scan would be extremely painful with our current global dcache.

But then again the global dcache isn't exactly a good idea to start
with.  If we had a per-sb dcache using e.g. the resizable hash table
the networking people seem to be fond off your idea would work really
well.