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From: Andrew Morton <akpm@linux-foundation.org>
To: Christoph Lameter <cl@linux-foundation.org>
Cc: rientjes@google.com, npiggin@suse.de, peterz@infradead.org,
	menage@google.com, dfults@sgi.com, linux-kernel@vger.kernel.org
Subject: Re: [patch 1/7] cpusets: add dirty map to struct address_space
Date: Tue, 4 Nov 2008 13:42:56 -0800	[thread overview]
Message-ID: <20081104134256.24db6b36.akpm@linux-foundation.org> (raw)
In-Reply-To: <Pine.LNX.4.64.0811041513490.23418@quilx.com>

On Tue, 4 Nov 2008 15:20:56 -0600 (CST)
Christoph Lameter <cl@linux-foundation.org> wrote:

> On Tue, 4 Nov 2008, Andrew Morton wrote:
> 
> >> +#ifdef CONFIG_CPUSETS
> >> +#if MAX_NUMNODES <= BITS_PER_LONG
> >> +	nodemask_t		dirty_nodes;	/* nodes with dirty pages */
> >> +#else
> >> +	nodemask_t		*dirty_nodes;	/* pointer to mask, if dirty */
> >> +#endif
> >> +#endif
> >>  } __attribute__((aligned(sizeof(long))));
> >
> > eek.  Increasing the size of the address_space (and hence of the inode)
> > is a moderately big deal - there can be millions of these in memory.
> 
> Well this is adding only a single word to the inode structure.

multiplied by millions.

> >> @@ -72,6 +72,8 @@ struct writeback_control {
> >>  	 * so we use a single control to update them
> >>  	 */
> >>  	unsigned no_nrwrite_index_update:1;
> >> +
> >> +	nodemask_t *nodes;		/* Nodemask to writeback */
> >
> > This one doesn't get ifdefs?
> 
> The structure is typically allocated temporarily on the stack.

An ifdef also helps catch the presence of unnecesary code.

> >> +	nodemask_t *nodes = mapping->dirty_nodes;
> >> +	int node = page_to_nid(page);
> >> +
> >> +	if (!nodes) {
> >> +		nodes = kmalloc(sizeof(nodemask_t), GFP_ATOMIC);
> >
> > erk, OK, called from __set_page_dirty, needs to be atomic.
> >
> > What are the consequences when this allocation fails?
> 
> Dirty tracking will not occur. All nodes are assumed to be dirty.

It won't oops?

> We discussed this earlier 
> http://www.ussg.iu.edu/hypermail/linux/kernel/0709.1/2291.html

Well, if it isn't in the changelog and isn't in code comments, we get
to discuss it again.

A great amount of mailing list discussion is a Huge Honking Big Fat
Hint that the original code was insufficently understandable.

  reply	other threads:[~2008-11-04 21:43 UTC|newest]

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-10-30 19:23 [patch 0/7] cpuset writeback throttling David Rientjes
2008-10-30 19:23 ` [patch 1/7] cpusets: add dirty map to struct address_space David Rientjes
2008-11-04 21:09   ` Andrew Morton
2008-11-04 21:20     ` Christoph Lameter
2008-11-04 21:42       ` Andrew Morton [this message]
2008-10-30 19:23 ` [patch 2/7] pdflush: allow the passing of a nodemask parameter David Rientjes
2008-10-30 19:23 ` [patch 3/7] mm: make page writeback obey cpuset constraints David Rientjes
2008-10-30 19:23 ` [patch 4/7] mm: cpuset aware reclaim writeout David Rientjes
2008-10-30 19:23 ` [patch 5/7] mm: throttle writeout with cpuset awareness David Rientjes
2008-10-30 19:23 ` [patch 6/7] cpusets: per cpuset dirty ratios David Rientjes
2008-10-30 19:23 ` [patch 7/7] cpusets: update documentation for writeback throttling David Rientjes
2008-10-30 21:08 ` [patch 0/7] cpuset " Dave Chinner
2008-10-30 21:33   ` Christoph Lameter
2008-10-30 22:03     ` Dave Chinner
2008-10-31 13:47       ` Christoph Lameter
2008-10-31 16:36       ` David Rientjes
2008-11-04 20:47 ` Andrew Morton
2008-11-04 20:53   ` Peter Zijlstra
2008-11-04 20:58     ` Christoph Lameter
2008-11-04 21:10     ` David Rientjes
2008-11-04 21:16     ` Andrew Morton
2008-11-04 21:21       ` Peter Zijlstra
2008-11-04 21:50         ` Andrew Morton
2008-11-04 22:17           ` Christoph Lameter
2008-11-04 22:35             ` Andrew Morton
2008-11-04 22:52               ` Christoph Lameter
2008-11-04 23:36                 ` Andrew Morton
2008-11-05  1:31                   ` KAMEZAWA Hiroyuki
2008-11-05  3:09                     ` Andrew Morton
2008-11-05  2:45                   ` Christoph Lameter
2008-11-05  3:05                     ` Andrew Morton
2008-11-05  4:31                       ` KAMEZAWA Hiroyuki
2008-11-10  9:02                         ` Andrea Righi
2008-11-10 10:02                           ` David Rientjes
2008-11-05 13:52                       ` Christoph Lameter
2008-11-05 18:41                         ` Andrew Morton
2008-11-05 20:21                           ` Christoph Lameter
2008-11-05 20:31                             ` Andrew Morton
2008-11-05 20:40                               ` Christoph Lameter
2008-11-05 20:56                                 ` Andrew Morton
2008-11-05 21:28                                   ` Christoph Lameter
2008-11-05 21:55                                   ` Paul Menage
2008-11-05 22:04                                   ` David Rientjes
2008-11-06  1:34                                     ` KAMEZAWA Hiroyuki
2008-11-06 20:35                                       ` David Rientjes
  -- strict thread matches above, loose matches on Subject: below --
2008-10-28 16:08 [patch 1/7] cpusets: add dirty map to struct address_space David Rientjes
2008-10-28 17:37 ` Peter Zijlstra
2008-10-28 20:48   ` David Rientjes
2008-10-29  1:13     ` David Rientjes
2008-10-29  2:24       ` David Rientjes
2008-10-30  8:38       ` Peter Zijlstra
2008-10-28 17:46 ` Peter Zijlstra
2008-10-28 19:19   ` David Rientjes

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