linux-kernel - Re: amusing SLUB compaction bug when CC_OPTIMIZE_FOR

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Message-Id: <66C933BF-D5AC-490F-81DC-601BE1DEEE60@joelfernandes.org>
Date:   Wed, 28 Sep 2022 15:53:04 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>
Cc:     Hugh Dickins <hughd@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: amusing SLUB compaction bug when CC_OPTIMIZE_FOR_SIZE


> On Sep 28, 2022, at 1:56 PM, Hyeonggon Yoo <42.hyeyoo@...il.com> wrote:
> 
> On Wed, Sep 28, 2022 at 06:20:10PM +0200, Vlastimil Babka wrote:
[..]
>>>> Thank you for report!
>>>> 
>>>> That should be due to commit 65505d1f2338e7
>>>> ("mm/sl[au]b: rearrange struct slab fields to allow larger rcu_head")
>>>> as now rcu_head can use some bits that shares with mapping.
>>>> 
>>>> Hmm IMO we have two choices...
>>>> 
>>>> 1. simply drop the commit as it's only for debugging (RCU folks may not like [1])
>>> 
>>> Yeah definitely don't like this option as patches are out that depend on
>>> this (not yet merged though). :-)
>> 
>> But we'll have to do that for now and postpone to 6.2 I'm afraid as merge
>> window for 6.1 is too close to have confidence in any solution that we came
>> up this moment.

I am ok with your postponing till then, gives me time to get other patches in, in the mean while :-)

Thanks again for your work on this,

 - Joel