Quoting Joonas Lahtinen (2017-09-27 09:52:42)
> On Mon, 2017-09-25 at 21:26 +0100, Chris Wilson wrote:
> > +static void *sys_thp_alloc(void *arg)
> > +{
> > + struct sys_wait *w = arg;
> > + struct timespec now;
> > +
> > + clock_gettime(CLOCK_MONOTONIC, &now);
> > + while (!done) {
> > + const size_t sz = 2 << 20;
> > + const struct timespec start = now;
> > + void *ptr;
> > +
> > + ptr = mmap(NULL, sz,
> > + PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS,
> > + -1, 0);
> > + assert(ptr != MAP_FAILED);
> > + madvise(ptr, sz, MADV_HUGEPAGE);
> > + for (int page = 0; page < 2 << 20 >> 12; page++)
> > + *((volatile uint32_t *)ptr + (page << 12 >> 2)) = 0;
>
> But what's the point in this iteration, we iterate from 0 to 512 page
> index (sz/PAGE_SIZE would be so much easier) and then write to to not
> each page but interleave four page writes per page and 3/4 of pages
> never get written? If this is intentional, please drop a comment.
- for (int page = 0; page < 2 << 20 >> 12; page++)
- *((volatile uint32_t *)ptr + (page << 12 >> 2)) = 0;
+ for (size_t page = 0; page < sz; page += PAGE_SIZE)
+ *(volatile uint32_t *)(ptr + page) = 0;
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