Re: [RFC v1 04/14] bus1: util - fixed list utility library

[David Herrmann]

Hi

On Thu, Oct 27, 2016 at 2:37 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> On Wed, Oct 26, 2016 at 09:18:00PM +0200, David Herrmann wrote:
>> +             e = kmalloc_array(sizeof(*e), BUS1_FLIST_BATCH + 1, gfp);
>
>> +#define BUS1_FLIST_BATCH (1024)
>
>> +struct bus1_flist {
>> +     union {
>> +             struct bus1_flist *next;
>> +             void *ptr;
>> +     };
>> +};
>
> So that's an allocation of 8*(1024+1), or slightly more than 2 pages.
>
> kmalloc will round up to the next power of two, so you'll end up with an
> allocation of 16*1024, wasting a whopping 8184 bytes per such allocation
> in slack space.
>
> Please consider using 1023 or something for your batch size, 511 would
> get you to exactly 1 page which would be even better.

Thanks for the hint! 511 looks like the obvious choice. Maybe even
(PAGE_SIZE / sizeof(long) - 1). I will put a comment next to the
definition.

Thanks
David