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SubjectRe: Unfreed kernel buffers (fsck and 2.3.99-pre*)


Linus Torvalds wrote:

> Can you try pre2-4 or later? It should have unbroken the breakage,

Indeed; it made the situation bearable again. :) Thanks!

There is _another_ issue, maybe an academic one, that I'd like to ask
about. Maybe someone could help illuminate the issue; it regards the
releasing of swapped pages.

Summary: If I open a suitably large text file in Emacs, and the system
swaps liberally, and the application is closed -- those swapped pages are
not immediately released in 2.3.99-pre* (up to pre3-5), but only upon
"demand".

Here's an example.

Starting situation, in X-windows, under 2.3.99-pre3-5:
total used free shared buffers cached
Mem: 30348 29776 572 0 284 22344
minus buffers/cache: 7148 23200
Swap: 32764 3008 29756

Now open a large Emacs session, go 23M into swap. Close Emacs. Then look:

total used free shared buffers cached
Mem: 30348 27136 3212 0 160 22748
minus buffers/cache: 4228 26120
Swap: 32764 17640 15124

Hmmm, there's nothing significant running anymore, yet 17M is shown paged
out. If I go and 'dd if=/dev/zero of=dump.dat bs=1024k count=40', or
attempt to allocate "relatively large" amounts of memory, _then_ those
swapped pages are freed and I get back to where I started:

total used free shared buffers cached
Mem: 30348 29568 780 0 552 21660
minus buffers/cache: 7356 22992
Swap: 32764 3644 29120


So... is it better to release swapped pages immediately, or only upon
"demand"? I would have naively guessed the former, but maybe I'm
missing a crucial point.

Thoughts?

Craig Kulesa
ckulesa@as.arizona.edu


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