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SubjectRe: memory management and the status of


On Mon, 7 Sep 1998, Chris Wedgwood wrote:

> On Sun, Sep 06, 1998 at 03:50:50PM +0200, Hans Eric wrote:
>
> > I thought linux already did this. It would be easy to refine the
> > swap algorithms to seek out dirty pages that has not been modified
> > for a while (lets say 2 minutes) and write them out to swap.
>
> Not modified isn't good enough, they have to be untouched, otherwise
> you'll start killing large databases which maintain large local
> caches and for many types or queries are RO. A example of this might
> be bind with lots of local authoritive domains.
>
> > Thus making them non dirty. Lets say this is done every 2 minutes
> > and only if the kernel has the idle cpu and disk io time, we dont
> > want to waste cpu and disk io that could have been used better. So
> > an idle linux box will then have a lots of non dirty pages that can
> > be used immidiately without any disk io for swapping if the need
> > for lots of memory suddenly comes up.
>
> Yes... and since many machines spend lots of time idle and many
> long-termed processes have many pages that pretty much aren't doing
> anything, we may as well use them for buffer-cache or whatever when
> the load does pick up.
>
> However, think more about this, it might be too hard or impossible to
> tune this for everyone.
>
> Consider the case of a large Oracle database that is used between 9am
> and 5pm. After 5pm, its fairly quiet, and the kernel starts migrating
> pages to disk... come the next morning, the database might initially
> be fairly sluggish as the kernel will have to page in plenty when the
> database gets busy....
>
For this case you might want to use my package "preload"
(http://www.math.upenn.edu/~vdergach/Linux) It has a module that allows
one to capture the current contents of the cache into a file and a program
that loads these files. (it doesn't capture the data, but which files
(and where) were actually loaded)

So you can capture the state of your cache in the evening , load it in the
morning and start off as if nothing happened.

Vladimir Dergachev


>
>
>
> -cw
>
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