Re: ~500 megs cached yet 2.6.5 goes into swap hell

Andrew Morton
2004-04-29T01:56:19Z

Paul Mackerras <paulus@samba.org> wrote:
>
> Andrew Morton writes:
>
> > My point is that decreasing the tendency of the kernel to swap stuff out is
> > wrong. You really don't want hundreds of megabytes of BloatyApp's
> > untouched memory floating about in the machine. Get it out on the disk,
> > use the memory for something useful.
>
> What I have noticed with 2.6.6-rc1 on my dual G5 is that if I rsync a
> gigabyte or so of data over to another machine, it then takes several
> seconds to change focus from one window to another. I can see it
> slowly redraw the window title bars. It looks like the window manager
> is getting swapped/paged out.
>
> This machine has 2.5GB of ram, so I really don't see why it would need
> to swap at all. There should be plenty of page cache pages that are
> clean and not in use by any process that could be discarded. It seems
> like as soon as there is any memory shortage at all it picks on the
> window manager and chucks out all its pages. :(
>

I suspect rsync is taking two passes across the source files for its
checksumming thing. If so, this will defeat the pagecache use-once logic.
The kernel sees the second touch of the pages and assumes that there will
be a third touch.

I use scp ;)