Re: [PATCH] pack-objects: only throw away data during memory pressure

From: Nicolas Pitre <nico@cam.org>
Date: Feb 13, 2008, 01:48 UTC
Message-ID: <alpine.LFD.1.00.0802122025490.2732@xanadu.home>
In-Reply-To: <alpine.LFD.1.00.0802110942310.2732@xanadu.home>

On Mon, 11 Feb 2008, Nicolas Pitre wrote:

Show 12 quoted lines

> On Mon, 11 Feb 2008, Martin Koegler wrote:
> 
> > If pack-objects hit the memory limit, it deletes objects from the delta
> > window.
> > 
> > This patch make it only delete the data, which is recomputed, if needed again.
> > 
> > Signed-off-by: Martin Koegler <mkoegler@auto.tuwien.ac.at>
> 
> Looks fine.
> 
> Acked-by: Nicolas Pitre <nico@cam.org>

Well, I take that back.

Some testing on the OOO repository with this turns out to be completely unusable.

By the time this gets into action and data is actively thrown away, performance simply goes down the drain due to the data constantly being reloaded over and over and over and over and over and over again, to the point of virtually making no relative progress at all.

So this change is not actually helping anything. The previous behavior of enforcing the memory limit by dynamically shrinking the window size at least had the effect of allowing some kind of progress, even if the end result wouldn't be optimal.

And that's the whole point behind this memory limiting feature: allowing some progress to be made when resources are too limited to let the repack go unbounded.

Therefore I think commit 9c2174350cc0ae0f6bad126e15fe1f9f044117ab should be reverted.

Nicolas