Re: [PATCH v2 4/9] dmapool: improve scalability of dma_pool_alloc

[Tony Battersby <tonyb@cybernetics.com>]

On 08/03/2018 05:02 AM, Andy Shevchenko wrote:
> On Thu, Aug 2, 2018 at 10:58 PM, Tony Battersby <tonyb@cybernetics.com> wrote:
>> dma_pool_alloc() scales poorly when allocating a large number of pages
>> because it does a linear scan of all previously-allocated pages before
>> allocating a new one.  Improve its scalability by maintaining a separate
>> list of pages that have free blocks ready to (re)allocate.  In big O
>> notation, this improves the algorithm from O(n^2) to O(n).
>>  struct dma_pool {              /* the pool */
>> +#define POOL_FULL_IDX   0
>> +#define POOL_AVAIL_IDX  1
>> +#define POOL_N_LISTS    2
>> +       struct list_head page_list[POOL_N_LISTS];
> To be consistent with naming scheme and common practice I would rather
> name the last one as
>
> POOL_MAX_IDX 2
OK.
>
>> +       INIT_LIST_HEAD(&retval->page_list[0]);
>> +       INIT_LIST_HEAD(&retval->page_list[1]);
> You introduced defines and don't use them.
>
Just a matter of style.A  In this context, it only matters that both
index 0 and 1 get initialized, not which index corresponds to which
list.A  But I suppose using the defines would improve keyword search, so
I'll change it.