linux-kernel - Re: [PATCH] fs/dcache.c: re-add cond_resched() in shrink_dcache

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Message-ID: <20180415005056.GX30522@ZenIV.linux.org.uk>
Date:   Sun, 15 Apr 2018 01:51:07 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Nikolay Borisov <nborisov@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Khazhismel Kumykov <khazhy@...gle.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        David Rientjes <rientjes@...gle.com>,
        Goldwyn Rodrigues <rgoldwyn@...e.de>,
        Jeff Mahoney <jeffm@...e.com>,
        Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [PATCH] fs/dcache.c: re-add cond_resched() in
 shrink_dcache_parent()

On Sat, Apr 14, 2018 at 02:47:21PM -0700, Linus Torvalds wrote:
> On Sat, Apr 14, 2018 at 1:58 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> >
> > That breaks d_invalidate(), unfortunately.  Look at the termination
> > conditions in the loop there...
> 
> Ugh. I was going to say "but that doesn't even use select_collect()",
> but yeah, detach_and_collect() calls it.
> 
> It would be easy enough to just change the
> 
>                 if (!list_empty(&data.select.dispose))
> 
> there to
> 
>                 if (!list_empty(&data.select.found))
> 
> too.

You would have to do the same in check_and_drop() as well,
and that brings back d_invalidate()/d_invalidate() livelock
we used to have.  See 81be24d263db...

I'm trying to put something together, but the damn thing is
full of potential livelocks, unfortunately ;-/  Will send
a followup once I have something resembling a sane solution...