Re: high iowait problem(Bug 12309 on bugzilla.kernel.org)

[Steven B]

Hi Andrew,

> So something between 2.6.32.3 and 2.6.32.8 inclusive rebroke the
> kernel.  That's useful info.
>
> Looking at the changelogs, the only thing I can immediately see in the
> block-core area is
>
> : commit cb723ba5d03bf719dbc7409b4d67572d4472ef8b
> : Author: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
> : Date:   Wed Jan 27 22:44:36 2010 +0300
> :
> :     block: fix bio_add_page for non trivial merge_bvec_fn case
>
> which seems unlikely.
>
> I'm seeing just one device-mapper change whcih went in over that
> timeframe:
>
> : commit e0f5cfa7c18b411634e73923841eccd3a4c0ce7f
> : Author: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
> : Date:   Mon Jan 11 03:21:50 2010 -0500
> :
> :     DM: Fix device mapper topology stacking
>
>

Although I can't provide any big details, I went through the commits between
2.6.32.2 and 2.6.32.8 and as many things that could affect IO and reverted
them from my 2.6.33.2 kernel.

Here's my list of commits I reverted that seemed to improve performance locally
running a 2.6.33.2 kernel.

cb723ba5d03bf719dbc7409b4d67572d4472ef8b (this one you suspected)
block: fix bio_add_page for non trivial merge_bvec_fn case

b2ea8cb9c8f1937cb80b9beb50548a05bfc37819
vmscan: do not evict inactive pages when skipping an active list scan

e4dd8ca5be771aa706b0797b3284328bb595bfa1
fasync: split 'fasync_helper()' into separate add/remove functions

Though, I was hoping you guys could identify which one of these is
the real culprit.


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