Re: [PATCH] 2/2 Prezeroing large blocks of pages during allocation Version 4

[Mel Gorman <mel@csn.ul.ie>]

On Tue, 8 Mar 2005, KAMEZAWA Hiroyuki wrote:

> Hi,
>
> Mel Gorman wrote:
>
> > +#define BITS_PER_ALLOC_TYPE 5
> > #define ALLOC_KERNNORCLM 0
> > #define ALLOC_KERNRCLM 1
> > #define ALLOC_USERRCLM 2
> > #define ALLOC_FALLBACK 3
> > +#define ALLOC_USERZERO 4
> > +#define ALLOC_KERNZERO 5
> >
>
> Now, 5bits per  MAX_ORDER pages.
> I think it is simpler to use "char[]" for representing type of  memory alloc
> type than bitmap.
>

Possibly, but it would also use up that bit more space. That map could be
condensed to 3 bits but would make it that bit (no pun) more complex and
difficult to merge. On the other hand, it would be faster to use a char[]
as it would be an array-index lookup to get a pageblock type rather than a
number of bit operations.

So, it depends on what people know to be better in general because I have
not measured it to know for a fact. Is it better to use char[] and use
array indexes rather than bit operations or is it better to leave it as a
bitmap and condense it later when things have settled down?

-- 
Mel Gorman
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