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SubjectRe: 2.4.0-test9-pre8
Hi!

> * Following a suggestion from Jeff Garzik to save the disk from heavy
> trashing during my mem=8M test, I've tried to use a ramdisk for
> swapping - Yes, I know, this is pretty stupid in normal use and might
> even be illegal (i.e. not expected to work by design). Anyway, I've
> tried it and was working when used as a swapdevice (size=64M, bs=4k).
> Added with priority 0 and the normal swap partition kept for fallback
> with prio=-1. No problems. It did even gracefully swapoff the ramdisk
> while it was already filled and the box was swapping to disk.
> To make thinks even more stupid, I've tried a second thing: create
> an ext2-fs (bs=4k) on the ramdisk, mount it, and use a swapfile on
> top of it. This deadlocks (with kswapd being current forever) at the
> very moment the swapfile ist filled and swapping has to go to the
> fallback raw swap partition.
> As already said, I wouldn't be surprised, if swapping to rd were
> broken. But swapping to a rd-partition appears solid while a rd-based
> swapfile deadlocks. Could the difference be explained somehow or might
> it indicate some deadlock path due to VM-fs interaction not
> covered otherwise - so far?

This really should be documented, somewhere.

For example swapping over nbd to localhost can not work.

Swapping over nbd to any other host can not work, too; but it might be
fixable.

Swapping to /dev/loop* probably can not work.

Swapping to file on nfs does not work.

Perhaps this should be added to Documentation/swap.txt?

(Rik, you know about this issues... Do you feel like creating
Documentation/swap.txt?)

Pavel
--
I'm pavel@ucw.cz. "In my country we have almost anarchy and I don't care."
Panos Katsaloulis describing me w.r.t. patents at discuss@linmodems.org
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