Re: kswapd busy but not swapping

From: Peter Zijlstra
Date: Wed May 21 2008 - 05:14:06 EST

On Wed, 2008-05-21 at 01:04 +0200, Christian Kujau wrote:
> Hi,
> I noticed that the [kswapd0] thread was eating 3-7% cpu time but no
> swapspace has been used yet. This is with a just booted system,
> currently with some disk i/o going on.
> So I figured that kswapd might not be responsible for "swapping" after
> all, although the name suggests it. Grep'ing Documentation/ for kswapd did
> not reveal much. Is the paper from Kanoj[0] still valid for 2.6 kernels?
> The SGI page referenced in Documentation/kernel-docs.txt is down, but
> there's a .txt version on [1] which tells me:
> "When memory runs low, and a process can not find a free page, it wakes
> up kswapd, the memory stealer"
> So, if I'd run low on memory, kswapd would be active. But I don't see that
> in free(1):
> # free -m
> total used free shared buffers cached
> Mem: 2023 1662 360 0 820 315
> -/+ buffers/cache: 526 1496
> Swap: 1505 0 1505

It could have been busy reclaiming pagecache.

kswapd is the generic reclaim thread - paging anonymous memory to the
swap is but one form thereof.

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