Messages in this thread | | | Date | Sat, 15 Dec 2001 05:27:55 -0800 | From | William Lee Irwin III <> | Subject | Re: [RFC] bootmem for 2.5 |
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On Fri, 2 Nov 2001, William Irwin wrote: >> [...] According to testing, this patch appears to save somewhere >> between 8KB and 2MB on i386 PC's versus the bitmap-based bootmem >> allocator.
On Sat, Dec 15, 2001 at 07:05:45AM +0100, Ingo Molnar wrote: > exactly where do these savings come from? The bootmem allocator frees its > bitmaps in free_all_bootmem().
I'm not entirely sure of the reason for the 2MB report, but it is the highest of the numbers that came back from #kernelnewbies testers.
In the common (i386) case, it's microscopic, and it's always a direct result of tracking allocations at address granularity as opposed to page granularity. The mainline bootmem (which I'm sure you yourself are quite familiar with =) tracks allocations at page granularity and maintains additional state for the last allocation in order to merge successive small allocations. There are other architectures (IA64) where larger differences are seen. The small memory savings are a nice side effect, but the primary benefit is intended to be less work being needed to initialize the allocator.
As a side note, I'm interested in your general opinion regarding the code, especially given your prior involvement with this subsystem.
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