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

Nick Piggin
2004-04-29T03:57:47Z

Andrew Morton wrote:
> 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'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.