Messages in this thread | | | Subject | Re: [PATCH 3/3] readahead: scale max readahead size depending on memory size | From | Peter Zijlstra <> | Date | Sun, 22 Jul 2007 10:36:45 +0200 |
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On Sun, 2007-07-22 at 10:24 +0200, Jens Axboe wrote: > On Sat, Jul 21 2007, Peter Zijlstra wrote:
> > +static __init int readahead_init(void) > > +{ > > + /* > > + * Scale the max readahead window with system memory > > + * > > + * 64M: 128K > > + * 128M: 180K > > + * 256M: 256K > > + * 512M: 360K > > + * 1G: 512K > > + * 2G: 724K > > + * 4G: 1024K > > + * 8G: 1448K > > + * 16G: 2048K > > + */ > > + ra_pages = int_sqrt(totalram_pages/16); > > + if (ra_pages > (2 << (20 - PAGE_SHIFT))) > > + ra_pages = 2 << (20 - PAGE_SHIFT); > > + > > + return 0; > > +} > > How did you come up with these numbers?
Well, most other places in the kernel where we scale by memory size we use the a sqrt curve, and the specific scale was the result of some fiddling, these numbers looked sane to me, nothing special.
Would you suggest a different set, and if so, do you have any rationale for them?
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