Re: [VM] 2.4.14/15-pre4 too "swap-happy"?

[Linus Torvalds]

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On Mon, 19 Nov 2001, Ken Brownfield wrote:
>
> I went straight to the aa patch, and it looks like it either fixes the
> problem or (because of the side-effects Linus mentioned) otherwise
> prevents the issue:

So is this pre6aa1, or pre6 + just the watermark patch?

> The machine went into swap immediately when the page cache stopped
> growing and hovered at 100-400MB.  Also, in my experience the page cache
> will grow until there's only 5ishMB of free RAM, but with the aa patch
> it looks like it stops at 320MB or maybe 10% of RAM.  Was that the aa
> patch, or part of -pre6?

That was the watermarking. The way Andrea did it, the page cache will
basically refuse to touch as much of the "normal" page zone, because it
would prefer to allocate more from highmem..

I think it's excessive to have 320MB free memory, though, that's just
an insane waste. I suspect that the real number should be somewhere
between the old behaviour and the new one. You can tweak the behaviour of
andrea's kernel by changing the "reserved" page numbers, but I'd like to
hear whether my simpler approach works too..

> The Oracle SGA is set to ~522MB, with nothing else running except a
> couple of sshds, getty, etc.  Now that I'm looking, 2.8GB page cache
> plus 328MB free adds up to about 3.1GB of RAM -- where does the 512MB
> shared memory segment fit?  Is it being swapped out in deference to page
> cache?

Shared memory actually uses the page cache too, so it will be accounted
for in the 2.8GB number.

Anyway, can you try plain vanilla pre6, with the appended patch? This is
my suggested simplified version of what Andrea tried to do, and it should
try to keep only a few extra megs of memory free in the low memory
regions, not 300+ MB.

(and the profiling would be interesting regardless, but I think Andrea did
find the real problem, his fix just seems a bit of an overkill ;)

		Linus

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