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SubjectRe: [PATCH 4/4] block: Optionally snapshot page contents to provide stable pages during write
On Fri, Dec 14, 2012 at 06:06:50PM -0800, Andy Lutomirski wrote:
> On Fri, Dec 14, 2012 at 6:01 PM, Darrick J. Wong
> <darrick.wong@oracle.com> wrote:
> > On Fri, Dec 14, 2012 at 05:12:37PM -0800, Andy Lutomirski wrote:
> >> It survived. I hit at least one mm bug, but I really don't think it's
> >> a problem with your code. (I have not tried this workload on Linux
> >> 3.7 at all before. It normally runs on 3.5.) The box in question is
> >
> > Would you mind sending along the bug report so I can make sure?
>
> http://marc.info/?l=linux-mm&m=135553342803210&w=2

Hm, this looks like a hugepages thing, which (afaik) doesn't touch fs code at
all. Looks like this patchset is in the clear.

> >
> >> ext4 on LVM on dm-crypt on (hardware) RAID 5 on hpsa, which should not
> >> need stable pages.
> >>
> >> The majority of the data written (that wasn't unlinked before it was
> >> dropped from cache) was checksummed when written and verified later.
> >> Most of this data was written using mmap. This workload hammers the
> >> vm concurrently in several threads, and it frequently stalls when
> >> stable pages are enabled, so it's probably exercising the code
> >> decently well.
> >
> > Did you observe any change in performance?
>
> No. But I'm comparing to 3.5 + butchery to remove stable pages. With
> stable pages on, this workload performs terribly. (It's a soft
> real-time thing, as you can possibly guess from my domain name, and
> various latency monitoring things go nuts when stable pages are
> active.)

Well, I guess that's good. :)

> Actually, performance appears to be improved, probably due to
> https://lkml.org/lkml/2012/12/14/14, which I tested concurrently.
>
> >
> >> Feel free to add Tested-by: Andy Lutomirski <luto@amacapital.net>
> >
> > Will do! Thanks for the testing!
>
> My pleasure. When these changes go in to an upstream kernel, they'll
> represent a significant reduction in how much our kernel differs from
> kernel.org's :) Thanks for fixing this.

No problem!

--D


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