Re: JFFS3 & performance

[Dan Post <postster@gmail.com>]

On Wed, 12 Jan 2005 17:34:53 +0000, David Woodhouse <dwmw2@infradead.org> wrote:
> We ought to be decompressing directly from flash to RAM. It takes 0.5x
> flash, and 1x RAM. And the RAM usage is dynamic -- you can throw the
> page away if memory is tight, and read it back again later.

Which can cause severe application performance problems in
RAM-constrained systems.  Your system will slow to a crawl if the page
cache is thrashed a lot... and I've seen this problem a number of
times.  If the page is always present, there is no page cache penalty
for executing code.

> And takes twice the amount of flash. Yes, it uses less RAM, but I don't
> see how it can reduce the ROM cost.
> I haven't seen a decent analysis of the real-life cost of startup -- the
> CELF numbers at OLS included decompression of the kernel in their
> startup timings.

We'll see what we can do to post numbers.
(No pun intended.)

Dan