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Re: [dm-devel] dm-cache mq policy warmup issue

Okay, a little correction here. The problematic setup was with 2.3TB cache, not 3TB. The mistake comes from the fact that at the time of the writing I was dealing with another server which has 8x480GB ssd's in raid5, which is little over 3TB. Obviously the number was floating in my head.

On Thu, Nov 14, 2013 at 4:37 PM, Joe Thornber <thornber redhat com> wrote:
On Wed, Nov 13, 2013 at 04:13:43PM +0000, Mears, Morgan wrote:
> On Mon, Nov 04, 2013 at 12:22:26PM -0500, Krishnasamy, Somasundaram wrote:
> > Mike,
> >
> > I was doing some testing with latest dm-cache code (from 'for-next' branch). I
> > am having difficulty in making the cache to warm-up. I used the below script
> > to read range of blocks repeatedly to get them promoted. I assume after
> > reading a block for mq->promote_threshold + 4 times, a block will be
> > promoted. But it is not happening. I also tested the same with the
> > sequential_threshold set to very high value.
> >
> > Cache warming-up was relatively easier in the previous dm-cache code. Is this
> > something you have seen in your testing?. Is there anything different should I
> > do?
> I'm also testing with the for-next branch of linux-dm.git and seeing the
> same thing as Somu.  It's easy to reproduce; reading the same block on the
> cached device over and over with dd does not result in that block being
> promoted.
> I did notice that the "read miss" counter for the cached device increments
> each time I execute dd, which I believe means this isn't a buffer cache
> issue (I also used dd iflag=direct).  The migration_threshold value
> shouldn't be an issue for this test, but I set it to a very high value
> anyway; didn't make any difference.
> Are there any tests in device-mapper-test-suite that you would recommend
> for testing whether promotions are occurring as expected?
> --Morgan

Hi Morgan,

I just added these tests, promotion is occuring, just not as much as I'd like:


Ah, these tests all trigger promotion via a write, I'll do some that just read.

- Joe

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