Feedback-ID: iad51458e:Fastmail
Date:   Thu, 26 Jan 2023 20:07:16 -0800
From:   Boqun Feng <boqun.feng@gmail.com>
To:     Chris Murphy <lists@colorremedies.com>
Cc:     Waiman Long <longman@redhat.com>,
        =?utf-8?B?0JzQuNGF0LDQuNC7INCT0LDQstGA0LjQu9C+0LI=?= 
        <mikhail.v.gavrilov@gmail.com>, David Sterba <dsterba@suse.cz>,
        Btrfs BTRFS <linux-btrfs@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
        Joel Fernandes <joel@joelfernandes.org>
Subject: Re: BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
Message-ID: <Y9NN9CFWc40oxmzP@boqun-archlinux>
References: <CABXGCsN+BcaGO0+0bJszDPvA=5JF_bOPfXC=OLzMzsXY2M8hyQ@mail.gmail.com>
 <20220726164250.GE13489@twin.jikos.cz>
 <CABXGCsN1rzCoYiB-vN5grzsMdvgm1qv2jnWn0enXq5R-wke8Eg@mail.gmail.com>
 <20230125171517.GV11562@twin.jikos.cz>
 <CABXGCsOD7jVGYkFFG-nM9BgNq_7c16yU08EBfaUc6+iNsX338g@mail.gmail.com>
 <Y9K6m5USnON/19GT@boqun-archlinux>
 <CABXGCsMD6nAPpF34c6oMK47kHUQqADQPUCWrxyY7WFiKi1qPNg@mail.gmail.com>
 <a8992f62-06e6-b183-3ab5-8118343efb3f@redhat.com>
 <7e48c1ec-c653-484e-88fb-69f3deb40b1d@app.fastmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <7e48c1ec-c653-484e-88fb-69f3deb40b1d@app.fastmail.com>
Precedence: bulk

On Thu, Jan 26, 2023 at 10:37:56PM -0500, Chris Murphy wrote:
> 
> 
> On Thu, Jan 26, 2023, at 7:20 PM, Waiman Long wrote:
> > On 1/26/23 17:42, Mikhail Gavrilov wrote:
> >>> I'm not sure whether these options are better than just increasing the
> >>> number, maybe to unblock your ASAP, you can try make it 30 and make sure
> >>> you have large enough memory to test.
> >> About just to increase the LOCKDEP_CHAINS_BITS by 1. Where should this
> >> be done? In vanilla kernel on kernel.org? In a specific distribution?
> >> or the user must rebuild the kernel himself? Maybe increase
> >> LOCKDEP_CHAINS_BITS by 1 is most reliable solution, but it difficult
> >> to distribute to end users because the meaning of using packaged
> >> distributions is lost (user should change LOCKDEP_CHAINS_BITS in
> >> config and rebuild the kernel by yourself).
> >
> > Note that lockdep is typically only enabled in a debug kernel shipped by 
> > a distro because of the high performance overhead. The non-debug kernel 
> > doesn't have lockdep enabled. When LOCKDEP_CHAINS_BITS isn't big enough 
> > when testing on the debug kernel, you can file a ticket to the distro 
> > asking for an increase in CONFIG_LOCKDEP_CHAIN_BITS. Or you can build 
> > your own debug kernel with a bigger CONFIG_LOCKDEP_CHAIN_BITS.
> 
> Fedora bumped CONFIG_LOCKDEP_CHAINS_BITS=17 to 18 just 6 months ago for debug kernels.
> https://gitlab.com/cki-project/kernel-ark/-/merge_requests/1921
> 
> If 19 the recommended value I don't mind sending an MR for it. But if
> the idea is we're going to be back here talking about bumping it to 20
> in six months, I'd like to avoid that.
> 

How about a boot parameter then?

Regards,
Boqun

> 
> 
> -- 
> Chris Murphy