Re: [Lhms-devel] [PATCH 0/7] Fragmentation Avoidance V19

Martin J. Bligh
2005-11-03T18:51:15Z

--Linus Torvalds <torvalds@osdl.org> wrote (on Thursday, November 03, 2005 10:44:14 -0800):

>
>
> On Thu, 3 Nov 2005, Martin J. Bligh wrote:
>> >
>> > These days we have things like per-cpu lists in front of the buddy
>> > allocator that will make fragmentation somewhat higher, but it's still
>> > absolutely true that the page allocation layout is _not_ random.
>>
>> OK, well I'll quit torturing you with incorrect math if you'll concede
>> that the situation gets much much worse as memory sizes get larger ;-)
>
> I don't remember the specifics (I did the stats several years ago), but if
> I recall correctly, the low-order allocations actually got _better_ with
> more memory, assuming you kept a fixed percentage of memory free. So you
> actually needed _less_ memory free (in percentages) to get low-order
> allocations reliably.

Possibly, I can redo the calculations easily enough (have to go for now,
but I just sent the other ones). But we don't keep a fixed percentage of
memory free - we cap it ... perhaps we should though?

M.