Messages in this thread | | | Date | Thu, 1 Dec 2005 20:11:01 +0800 | From | Wu Fengguang <> | Subject | Re: [PATCH 02/12] mm: supporting variables and functions for balanced zone aging |
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On Thu, Dec 01, 2005 at 02:37:14AM -0800, Andrew Morton wrote: > Wu Fengguang <wfg@mail.ustc.edu.cn> wrote: > > > > The zone aging rates are currently imbalanced, > > ZONE_DMA is out of whack. It shouldn't be, and I'm not aware of anyone > getting in and working out why. I certainly wouldn't want to go and add > all this stuff without having a good understanding of _why_ it's out of > whack. Perhaps it's just some silly bug, like the thing I pointed at in > the previous email.
Yep, my rule is that if ever the DMA zone is reclaimed for watermark, it will be running wild ;) So I leave it out by setting classzone_idx=0, and let the age balancing code to catch it up. This scheme works fine: tested to be OK from 64M to 2G memory.
> > the gap can be as large as 3 times, > > What's the testcase? > > > which can severely damage read-ahead requests and shorten their > > effective life time. > > Have you any performance numbers for this?
That's months ago, if I remember it right, the number of concurrent readers the adaptive read-ahead code can handle without much thrashing was raised from ~100 to 800 with the balancing work.
This is my original announce back then:
The page aging problem showed up when I was testing many slow reads with limited memory. Pages in the DMA zone were found out to be aged about 3 times faster than that of Normal zone in systems with 64-512M memory. That is a BIG threat to the read-ahead pages. So I added some code to make the aging rates synchronized. You can see the effect by running: $ tar c / | cat > /dev/null & $ watch -n1 'grep "age " /proc/zoneinfo' There are still some extra DMA scans in the direct page reclaim path. It tend to happen in large memory system and is therefore not a big problem.
And here is some numbers collected by Magnus Damm: http://lkml.org/lkml/2005/10/25/50
Good night! Wu - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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