Re: [PATCH] cpuset confine pdflush to its cpuset

Re: [PATCH] cpuset confine pdflush to its cpuset

[Hirokazu Takahashi]

Hi Paul,

I realized CPUSETS has another problem around pdflush.

Some cpuset may make most of pages in it dirty, while the others don't.
In this case, pdflush may not start since the ratio of the dirty pages
in the box may be less than the watermark, which is defined globally.
This may probably make it hard to allocate pages from the cpuset
or the nodes it depends on. This wouldn't be good for NUMA machine
without cpusets either.

Do you have any plans about it?

> This patch keeps pdflush daemons on the same cpuset as their
> parent, the kthread daemon.
> 
> Some large NUMA configurations put as much as they can of
> kernel threads and other classic Unix load in what's called a
> bootcpuset, keeping the rest of the system free for dedicated
> jobs.
> 
> This effort is thwarted by pdflush, which dynamically destroys
> and recreates pdflush daemons depending on load.


Thanks,
Hirokazu Takahashi.

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Re: [PATCH] cpuset confine pdflush to its cpuset

[Paul Jackson]

Takahashi-san wrote:
> I realized CPUSETS has another problem around pdflush.

Excellent observation.  I had not realized this.

Thank-you for pointing it out.

I don't have plans.  Do you have any suggestions?

  ( Anyone know what the "pd" stands for in pdflush ?? )

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Re: [PATCH] cpuset confine pdflush to its cpuset

[Andrew Morton]

Paul Jackson <pj@sgi.com> wrote:
>
> Takahashi-san wrote:
> > I realized CPUSETS has another problem around pdflush.
> 
> Excellent observation.  I had not realized this.
> 
> Thank-you for pointing it out.
> 
> I don't have plans.  Do you have any suggestions?

Per-zone dirty thresholds (quite messy), per-zone writeback (horrific,
linear searches or data structure proliferation everywhere).

Let's see a (serious) worload/testcase first, hey?  vmscan.c writeback off
the LRU is a bit slow, but we should be able to make it suffice.

>   ( Anyone know what the "pd" stands for in pdflush ?? )

"page dirty"?  It's what bdflush became when writeback went from
being block-based to being page-based.

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Re: [PATCH] cpuset confine pdflush to its cpuset

[Paul Jackson]

Andrew wrote:
> Let's see a (serious) worload/testcase first, hey?

A reasonable request.


> >   ( Anyone know what the "pd" stands for in pdflush ?? )
> 
> "page dirty"?  It's what bdflush became ...

Ah - thanks.

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Re: [PATCH] cpuset confine pdflush to its cpuset

[Hirokazu Takahashi]

Hi Paul,

> Andrew wrote:
> > Let's see a (serious) worload/testcase first, hey?
> 
> A reasonable request.

Can you do this?
I think you may probably use a large NUMA machine.

> > >   ( Anyone know what the "pd" stands for in pdflush ?? )
> > 
> > "page dirty"?  It's what bdflush became ...
> 
> Ah - thanks.

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Re: [PATCH] cpuset confine pdflush to its cpuset

[Paul Jackson]

Takahashi-san replied to pj:
> > A reasonable request.
> 
> Can you do this?
> I think you may probably use a large NUMA machine.

In theory, yes.  I certainly have access to large NUMA machines.

However, it is likely not a priority for me.  My focus is on work that
will benefit workloads that do not depend on pdflush (except to want to
be sure that pdflush is -not- running in a cpuset containing a dedicated
job.)

That seems to keep me busy enough (and keep my employer paying me),
so I might never get to this problem.  I might, but the odds are
not good.

Sorry.

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                  Programmer, Linux Scalability
                  Paul Jackson <pj@sgi.com> 1.925.600.0401

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