Re: [PATCH] Bias the location of pages freed for min_free_kbytes in the same MAX_ORDER_NR_PAGES blocks

Andrew Morton
2007-03-18T19:28:39Z

On Sun, 18 Mar 2007 19:05:41 +0000 (GMT) Mel Gorman <mel@csn.ul.ie> wrote:

> > How much additional memory consumption are we expecting here?
> >
>
> Short answer, about 1.5KB on a 1GB system of which 1.3KB is statically
> defined in the 3 struct zones on a 1 node x86 system.
>
> Longer answer that I hopefully have not made any mistakes in - There is
> the zone overhead which is statically sized and a runtime overhead which
> depends on the amount of memory in the system. The additional zone
> overhead is the overhead for additional freelists (larger struct
> free_area) and is as follows;
>
> (MIGRATE_TYPES-1) * sizeof(list_head) * (MAX_ORDER-1)
>
> so, on 32 bit in general, thats
>
> 4 * 8 * 10 = 320 bytes per zone (would be 240 bytes if MIGRATE_RESERVE is
> sufficient for higher order allocations
> instead of MIGRATE_HIGHALLOC)
>
> on x86 with DMA, Normal and HighMem, thats 1280 bytes. On a NUMA system,
> it's 1280 bytes per node. On 64 bit, it would be double because of the
> larger pointer size. At worst, I guess you are looking at 3KB per node.

That a very modest overhead - not worth the config option, IMO.

The runtime overhead might be a concern - is it possible to quantify
it?