Hi KOSAKi,

On Tue, Jul 12, 2011 at 6:40 PM, KOSAKI Motohiro
[off-list ref] wrote:

(2011/07/12 18:27), Minchan Kim wrote:

quoted

Hi Mel,

On Mon, Jul 11, 2011 at 10:01 PM, Mel Gorman [off-list ref] wrote:

quoted

Zone reclaim is similar to direct reclaim in a number of respects.
PF_SWAPWRITE is used by kswapd to avoid a write-congestion check
but it's set also set for zone_reclaim which is inappropriate.
Setting it potentially allows zone_reclaim users to cause large IO
stalls which is worse than remote memory accesses.

As I read zone_reclaim_mode in vm.txt, I think it's intentional.
It has meaning of throttle the process which are writing large amounts
of data. The point is to prevent use of remote node's free memory.

And we has still the comment. If you're right, you should remove comment.
"         * and we also need to be able to write out pages for RECLAIM_WRITE
         * and RECLAIM_SWAP."


And at least, we should Cc Christoph and KOSAKI.

Of course, I'll take full ack this. Do you remember I posted the same patch
about one year ago. At that time, Mel disagreed me and I'm glad to see he changed
the mind. :)

I remember that but I don't know why Mel didn't ack at that time.
http://lkml.org/lkml/2010/8/5/44

Anyway, Hannes's bd2f6199cf is to introduce lumpy reclaim of
zone_reclaim so it's natural to increase latency for getting big order
pages(ie, it's a trade-off).

And as I read about zone_reclaim_mode in Documentation/sysctl/vm.txt,
I think big latency(ie, throttling of the process) is intentional to
prevent stealing pages for other nodes.

If I am not against this patch, at least, we need agreement of
Christoph and others and if we agree this change, we changes vm.txt,
too.


-- 
Kind regards,
Minchan Kim

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