Write-back/VM question

Write-back/VM question

[Rajagopal Ananthanarayanan]

One of the behaviors of the new VM seems
to be that it starts I/O on a written page
fairly early. This "aggressive" write is
great for streaming I/O, but seems to have
a penalty when the application has write-locality.
Dbench is a one case, which is write intensive
and a lot of the writes are to a previously written page.

I'm not exactly certain why starting write-out
early would cause problems, but I've a couple of
quick questions:

1. Is the page locked during write-out?

2. Is there a tuneable that I can use to
   control write-back behaviour?

thanks!


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Rajagopal Ananthanarayanan ("ananth")
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Re: Write-back/VM question

[Rik van Riel]

On Mon, 9 Oct 2000, Rajagopal Ananthanarayanan wrote:

> One of the behaviors of the new VM seems to be that it starts
> I/O on a written page fairly early. This "aggressive" write is
> great for streaming I/O, but seems to have a penalty when the
> application has write-locality. Dbench is a one case, which is
> write intensive and a lot of the writes are to a previously
> written page.
> 
> I'm not exactly certain why starting write-out early would cause
> problems, but I've a couple of quick questions:
> 
> 1. Is the page locked during write-out?

The buffers on the page are. I'm not sure about the page
itself though ...

> 2. Is there a tuneable that I can use to
>    control write-back behaviour?

/proc/sys/vm/bdflush, first value

regards,

Rik
--
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