Re: [PATCH 3/4] ida: in-place ida allocation

[Tejun Heo]

On Tue, Apr 22, 2014 at 06:16:20PM +0800, Lai Jiangshan wrote:
> There are two stages of ida allocation/free, idr_layers and ida_bitmap.
> They add unneeded foot print and memory waste.
> 
> When a single ID is first allocated from an ida, this ida requires
> two big chunks of memory. One idr_layer and one ida_bitmap.
> 
> To reduce the foot print and memory, we reduce the ida_bitmap
> to a single "unsigned long" and place it in its own idr-slot
> and avoid to allocate the ida_bitmap.
> 
> It also means ida bitmap is located on its coresponding idr-slot
> which size is the same as "unsigned long".
> Each ida bitmap(idr-slot) contains BITS_PER_LONG ida-slots.
> 
> The struct ida_bitmap is not needed any more, we use "unsigned long"
> directly and remove all the code of alloc/free struct ida_bitmap.

Are you calling 128 byte a "big chunk of memory" while trading off
tree depth for it?  No, this level of space optimizaiton is completely
uncalled for.

 Nacked-by: Tejun Heo <tj@xxxxxxxxxx>

Thanks.

-- 
tejun
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