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Date: Sun, 5 Aug 2018 05:50:04 -0700
From: Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH] mm: Use special value SHRINKER_REGISTERING instead
 list_empty() check
Message-ID: <20180805125004.GD3183@bombadil.infradead.org>
References: <153331055842.22632.9290331685041037871.stgit@localhost.localdomain>
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 <843169c5-a47a-e6cd-7412-611e72eb20ba@virtuozzo.com>
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To: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, vdavydov.dev@gmail.com, mhocko@suse.com, aryabinin@virtuozzo.com, ying.huang@intel.com, penguin-kernel@I-love.SAKURA.ne.jp, shakeelb@google.com, jbacik@fb.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org

On Sun, Aug 05, 2018 at 08:30:43AM +0300, Kirill Tkhai wrote:
> On 05.08.2018 03:03, Matthew Wilcox wrote:
> > On Sat, Aug 04, 2018 at 09:42:05PM +0300, Kirill Tkhai wrote:
> >> This is exactly the thing the patch makes. Instead of inserting a shrinker pointer
> >> to idr, it inserts a fake value SHRINKER_REGISTERING there. The patch makes impossible
> >> to dereference a shrinker unless it's completely registered. 
> > 
> > -       id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
> > +       id = idr_alloc(&shrinker_idr, SHRINKER_REGISTERING, 0, 0, GFP_KERNEL);
> > 
> > Instead:
> > 
> > +       id = idr_alloc(&shrinker_idr, NULL, 0, 0, GFP_KERNEL);
> > 
> > ... and the rest of your patch becomes even simpler.
> 
> The patch, we are discussing at the moment, does *exactly* this:
> 
> https://lkml.org/lkml/2018/8/3/588
> 
> It looks like you missed this hunk in the patch.

No, it does this:

+       id = idr_alloc(&shrinker_idr, SHRINKER_REGISTERING, 0, 0, GFP_KERNEL);

I'm saying do this:

+       id = idr_alloc(&shrinker_idr, NULL, 0, 0, GFP_KERNEL);