linux-kernel - Re: [PATCH 11/18] fs: Introduce per-bucket inode hash locks

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Message-ID: <AANLkTikeozj07Re34hS1Y-i8E90tqYy9kraVHs7MOkqg@mail.gmail.com>
Date:	Mon, 25 Oct 2010 18:12:40 -0600
From:	Nick Piggin <npiggin@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Nick Piggin <npiggin@...nel.dk>,
	Christoph Hellwig <hch@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Dave Chinner <david@...morbit.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 11/18] fs: Introduce per-bucket inode hash locks

On Mon, Oct 25, 2010 at 1:04 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Mon, 25 Oct 2010, Thomas Gleixner wrote:
>> On Mon, 25 Oct 2010, Nick Piggin wrote:
>> > Although a sane locking macro and structure like I had, would perfectly
>> > allow you to switch locks in a single place just the same.
>>
>> And a locking macro/structure is better in self documenting than a
>> helper function which was proposed by Christoph?
>
> Independently of what data structure you folks agree on, we really do
> _NOT_ want to have open coded bit_spin_*lock() anywhere in the code.
>
> As I said before, aside of RT it's a basic requirement to switch bit
> spinlocks to real ones for lockdep debugging.

Putting it in hlist_bl locking function doesn't do much to help --
putting mutexes
or spinlocks into hlist hashes is insane.

What might be good is to have a bit spinlock structure which is 0 size
in a normal
config, but it can hold things like lockdep data. Someone posted a patch maybe a
year ago to do that, which I thought was good but I don't know why it didn't go
anywhere.

It still doesn't solve your -rt problem really, because on a
production rt build like I
say, you can't blindly just replace bit spinlocks with mutexes. But it
makes lockdep
work and could take care of *some* bit spinlocks for -rt.
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