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

[Nick Piggin]

Andrew Morton wrote:
> Paul Mackerras <paulus@xxxxxxxxx> 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'm not very impressed with the pagecache use-once logic, and I
have a patch to remove it completely and treat non-mapped touches
(IMO) more sanely.
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