linux-kernel - Re: [PATCH] Use extents for recording what swap is allocated.

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Message-Id: <1161731101.22729.44.camel@nigel.suspend2.net>
Date:	Wed, 25 Oct 2006 09:05:01 +1000
From:	Nigel Cunningham <ncunningham@...uxmail.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Andrew Morton <akpm@...l.org>, LKML <linux-kernel@...r.kernel.org>,
	Pavel Machek <pavel@....cz>
Subject: Re: [PATCH] Use extents for recording what swap is allocated.

Hi.

On Wed, 2006-10-25 at 00:45 +0200, Rafael J. Wysocki wrote:
> Hi,
> 
> On Wednesday, 25 October 2006 00:13, Nigel Cunningham wrote:
> > Hi.
> > 
> > On Tue, 2006-10-24 at 22:08 +0200, Rafael J. Wysocki wrote:
> > > On Monday, 23 October 2006 06:14, Nigel Cunningham wrote:
> > > > Switch from bitmaps to using extents to record what swap is allocated;
> > > > they make more efficient use of memory, particularly where the allocated
> > > > storage is small and the swap space is large.
> > > 
> > > As I said before, I like the overall idea, but I have a bunch of comments.
> > 
> > Thanks for them. Just a quick reply for the moment to say they're
> > appreciated and I will revise accordingly.
> > 
> > I should also mention that this isn't the only use of these functions in
> > Suspend2.
> 
> Could we please focus on things that are on the table _now_?.  You are
> submitting the patch aganist the current code and I can only review it
> in this context.  I can't say if I like your _future_ patches at this moment! :-)

I understand that, but some things won't make sense or seem as useful if
I don't give you the extra information.

> > There I also use extents to record the blocks to which the 
> > image will be written. I hope to submit modifications to swsusp to do
> > that too in the near future.
> > 
> > > > +/* Simplify iterating through all the values in an extent chain */
> > > > +#define suspend_extent_for_each(extent_chain, extentpointer, value) \
> > > > +if ((extent_chain)->first) \
> > > > +	for ((extentpointer) = (extent_chain)->first, (value) = \
> > > > +			(extentpointer)->minimum; \
> > > > +	     ((extentpointer) && ((extentpointer)->next || (value) <= \
> > > > +				 (extentpointer)->maximum)); \
> > > > +	     (((value) == (extentpointer)->maximum) ? \
> > > > +		((extentpointer) = (extentpointer)->next, (value) = \
> > > > +		 ((extentpointer) ? (extentpointer)->minimum : 0)) : \
> > > > +			(value)++))
> > > 
> > > This macro doesn't look very nice and is used only once, so I think you
> > > can drop it and just write the loop where it belongs.
> > 
> > With the modifications I mentioned just above, this would also be used
> > for getting the blocks which match each swap extent. I can remove the
> > macro, but just want to make you aware that it does serve a purpose,
> > you're just not seeing it fully yet.
> 
> Can we just assume there are no other patches and proceed under this
> assumption?
> 
> Could you please remove the macro for now?  You can introduce it with the
> other patches when you submit them (if it's still needed at that time).

Ok.

Nigel

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