On Fri, 2019-01-04 at 10:31 +0530, Arun KS wrote:
> When freeing pages are done with higher order, time spent on coalescing
> pages by buddy allocator can be reduced. With section size of 256MB, hot
> add latency of a single section shows improvement from 50-60 ms to less
> than 1 ms, hence improving the hot add latency by 60 times. Modify
> external providers of online callback to align with the change.
>
> Signed-off-by: Arun KS <[email protected]>
> Acked-by: Michal Hocko <[email protected]>
> Reviewed-by: Oscar Salvador <[email protected]>
After running into my initial issue I actually had a few more questions
about this patch.
> [...]
> +static int online_pages_blocks(unsigned long start, unsigned long nr_pages)
> +{
> + unsigned long end = start + nr_pages;
> + int order, ret, onlined_pages = 0;
> +
> + while (start < end) {
> + order = min(MAX_ORDER - 1,
> + get_order(PFN_PHYS(end) - PFN_PHYS(start)));
> +
> + ret = (*online_page_callback)(pfn_to_page(start), order);
> + if (!ret)
> + onlined_pages += (1UL << order);
> + else if (ret > 0)
> + onlined_pages += ret;
> +
> + start += (1UL << order);
> + }
> + return onlined_pages;
> }
>
Should the limit for this really be MAX_ORDER - 1 or should it be
pageblock_order? In some cases this will be the same value, but I seem
to recall that for x86 MAX_ORDER can be several times larger than
pageblock_order.
> static int online_pages_range(unsigned long start_pfn, unsigned long
> nr_pages,
> void *arg)
> {
> - unsigned long i;
> unsigned long onlined_pages = *(unsigned long *)arg;
> - struct page *page;
>
> if (PageReserved(pfn_to_page(start_pfn)))
I'm not sure we even really need this check. Getting back to the
discussion I have been having with Michal in regards to the need for
the DAX pages to not have the reserved bit cleared I was originally
wondering if we could replace this check with a call to
online_section_nr since the section shouldn't be online until we set
the bit below in online_mem_sections.
However after doing some further digging it looks like this could
probably be dropped entirely since we only call this function from
online_pages and that function is only called by memory_block_action if
pages_correctly_probed returns true. However pages_correctly_probed
should return false if any of the sections contained in the page range
is already online.
> - for (i = 0; i < nr_pages; i++) {
> - page = pfn_to_page(start_pfn + i);
> - (*online_page_callback)(page);
> - onlined_pages++;
> - }
> + onlined_pages = online_pages_blocks(start_pfn, nr_pages);
>
> online_mem_sections(start_pfn, start_pfn + nr_pages);
>
