linux-kernel - Re: [PATCH 2/2] block: Convert BDI proportion calculations to flexible proportions

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Message-ID: <20120531221146.GA19050@quack.suse.cz>
Date:	Fri, 1 Jun 2012 00:11:46 +0200
From:	Jan Kara <jack@...e.cz>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jan Kara <jack@...e.cz>, Sasha Levin <levinsasha928@...il.com>,
	Wu Fengguang <fengguang.wu@...el.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] block: Convert BDI proportion calculations to
 flexible proportions

On Tue 29-05-12 14:54:52, Jan Kara wrote:
> On Tue 29-05-12 14:38:31, Peter Zijlstra wrote:
> > On Tue, 2012-05-29 at 14:34 +0200, Jan Kara wrote:
> > 
> > > The only safe solution seems to be to create a variant of percpu counters
> > > that can be used from an interrupt. Or do you have other idea Peter?
> > 
> > > > [   20.680186]  [<ffffffff8325ac9b>] _raw_spin_lock+0x3b/0x70
> > > > [   20.680186]  [<ffffffff81993527>] ? __percpu_counter_sum+0x17/0xc0
> > > > [   20.680186]  [<ffffffff81993527>] __percpu_counter_sum+0x17/0xc0
> > > > [   20.680186]  [<ffffffff810ebf90>] ? init_timer_deferrable_key+0x20/0x20
> > > > [   20.680186]  [<ffffffff8195b5c2>] fprop_new_period+0x12/0x60
> > > > [   20.680186]  [<ffffffff811d929d>] writeout_period+0x3d/0xa0
> > > > [   20.680186]  [<ffffffff810ec0bf>] call_timer_fn+0x12f/0x260
> > > > [   20.680186]  [<ffffffff810ebf90>] ? init_timer_deferrable_key+0x20/0x20
> > 
> > Yeah, just make sure IRQs are disabled around doing that ;-)
>   Evil ;) But we'd need to have IRQs disabled also in each
> fprop_fraction_percpu() call, and generally, if we want things clean, we'd
> need to disable them in all entry points to proportion code (or at least
> around all percpu calls)...
  OK, after some thought I was wrong and fixing fprop_new_period() is
enough. Attached patch should fix the warning (and possible deadlock).
Fengguang should I resend you fixed patch implementing flexible proportions
or do you prefer incremental patch against your tree?

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR

View attachment "flex-proportion-irq-save.diff" of type "text/x-patch" (1286 bytes)