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

[Andrew Morton <akpm@osdl.org>]

Paul Mackerras <paulus@samba.org> wrote:
>
> Andrew Morton writes:
> 
> > OK, a bit of fiddling does indicate that if a file is present on both
> > client and server, and is modified on the client, the rsync client will
> > indeed touch the pagecache pages twice.  Does this describe the files which
> > you're copying at all?
> 
> The client/server thing is a bit misleading, what matters is the
> direction of the transfer.  In the case I saw this morning, the G5 was
> the sender.  In any case I was using the -W switch, which tells it not
> to use the rsync algorithm but just transfer the whole file.  So I
> believe that rsync on the G5 side was just reading the file through
> once.
> 
> I have also noticed similar behaviour after doing a bk pull on a
> kernel tree.
> 
> The really strange thing is that the behaviour seems to get worse the
> more RAM you have.  I haven't noticed any problem at all on my laptop
> with 768MB, only on the G5, which has 2.5GB.  (The laptop is still on
> 2.6.2-rc3 though, so I will try a newer kernel on it.)
> 

Is the laptop x86 or ppc?  IIRC there were problems with the pte-referenced
handling on ppc?  Or was it ppc64?  It shouldn't make any difference in
this case I guess.

To investigate this sort of thing you're better off using just a local `dd'
to ascertain the pattern which is causing the problem.  Keep things simple.

What happens if you do a 4G writeout with dd?  Is there any swapout?  There
shouldn't be much at all.  If the big dd indeed does not cause swapout,
then what is different about rsync?