Re: [PATCH] vm - swap_prefetch v12

[Andrew Morton]

Con Kolivas <kernel@xxxxxxxxxxx> wrote:
>
> On Fri, 30 Sep 2005 07:54 am, Andrew Morton wrote:
> > Con Kolivas <kernel@xxxxxxxxxxx> wrote:
> > > Once pages have been added to the swapped list, a timer is started,
> > > testing for conditions suitable to prefetch swap pages every 5 seconds.
> > > Suitable conditions are defined as lack of swapping out or in any pages,
> > > and no watermark tests failing. Significant amounts of dirtied ram also
> > > prevent prefetching. It then checks that we have spare ram looking for at
> > > least 3* pages_high free per zone and if it succeeds that will prefetch
> > > pages from swap.
> >
> > Did you consider poking around in gendisk.disk_stats to determine whether
> > the swap disk(s) are idleish?
> 
> I didn't know where to look for that info. Thanks! I'm open to *any* 
> suggestions and I'll look into it as I can't take this code much further 
> without outside help.
> 

Might also be able to utilise CFQ's I/O priorities.  That should be more
efective than a heuristic based on disk_stats, however you'd probably need
to work out whether the swapdev actually supports IO priorities and I'm not
sure how one would query that (cleanly).

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