Re: why swap at all?

[Nick Piggin]

Buddy Lumpkin wrote:
> -----Original Message-----
> From: William Lee Irwin III [mailto:wli@xxxxxxxxxxxxxx] 
> Sent: Wednesday, May 26, 2004 2:09 AM
> To: Buddy Lumpkin
> Cc: orders@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: why swap at all?
>
> On Wed, May 26, 2004 at 01:30:09AM -0700, Buddy Lumpkin wrote:
>
> > As for your short, two sentence comment below, let me save you the energy
>
> of
>
> > insinuations and translate your message the way I read it: 
> > -------------------------------------------------------------------------
> > I don't recognize your name, therefore you can't possibly have a valuable
> > opinion on the direction VM system development should go. I doubt you have
> > an actual performance problem to share, but if you do, please share it and
> > go away so that we can work on solving the problem.
> > --------------------------------------------------------------------------
> > My response:
> > Get over yourself.
>
>
> > What the Hell? I have enough bugs I'm paid to fix that I'm not going to
> > tolerate harassment for requesting that claims that the kernel behaves
> > pathologically in some scenario be cast as comprehensible bugreports.
> > It's also worth noting that paying customers don't respond so uncouthly.
>
>
>
> > -- wli
>
>
> If you follow the thread, you will see no claim from me that there is
> anything wrong with the kernel. I simply stated that the priority of VM
> system development should focus on physical memory, and that physical memory
> access should not suffer as a result of some tradeoff that improves the
> performance of the VM system when free physical memory is low and there is
> heavy use of the swap device.

You also went on to say:
> This of course doesn't address the VM paging storms that happen due to large
> amounts of file system writes. Once the pagecache fills up, dirty pages must
> be evicted from the pagecache so that new pages can be added to the
> pagecache.

By and large, Linux doesn't reclaim dirty pages from the pagecache,
and it should not have paging storms due to large amounts of file
system writes.

If you had a workload where it does, we would be interested to see
it. I pointed out to you that this is what Bill was asking you to
file a detailed report about.

> I can't speak whether or not a case like this currently exists, but I know
> optimizing swap performance is a very complicated yet captivating subject
> that has consumed many a posts on this list. People have tried to optimize
> every part of the VM before, so I was just calling out what I believe to be
> a very reasonable and practical goal and put a little bit of substance
> around why I think it's practical.

Actually, during the 2.5 development cycle, swapping performance
got fairly neglected to the point where we were performing twice
as bad as 2.4 for most things. I (and others) recently improved
this because real people doing real things were complaining.

[snip rant]

> I can picture where this is going. Here is an interview between you and a
> popular Linux magazine in two years:
>
>
> Linux Magazine: You have contributed to linux for quite some time, correct?
>
> William: Oh yes, it is my hobby and occupation. I love my work.
>
> Linux Magazine: You have done all these wonderful things!
>
> William: Thanks, I am very proud of that
>
> Linux Magazine: Why did you make such and such decision that backfired?
>
> William: I don't have to answer that, I don't owe you anything and your not
> a paying customer.
>
> Give me a break.

What?? Give *you* a break? From a fictional interview you concocted?

Give me a break.
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