On Wed, 21 Nov 2012 23:09:46 +0800
Jiang Liu <liuj97@xxxxxxxxx> wrote:
> Subject: Re: [RFT PATCH v2 4/5] mm: provide more accurate estimation of pages occupied by memmap
How are people to test this? "does it boot"?
> If SPARSEMEM is enabled, it won't build page structures for
> non-existing pages (holes) within a zone, so provide a more accurate
> estimation of pages occupied by memmap if there are bigger holes within
> the zone.
>
> And pages for highmem zones' memmap will be allocated from lowmem, so
> charge nr_kernel_pages for that.
>
> ...
>
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4442,6 +4442,26 @@ void __init set_pageblock_order(void)
>
> #endif /* CONFIG_HUGETLB_PAGE_SIZE_VARIABLE */
>
> +static unsigned long calc_memmap_size(unsigned long spanned_pages,
> + unsigned long present_pages)
> +{
> + unsigned long pages = spanned_pages;
> +
> + /*
> + * Provide a more accurate estimation if there are holes within
> + * the zone and SPARSEMEM is in use. If there are holes within the
> + * zone, each populated memory region may cost us one or two extra
> + * memmap pages due to alignment because memmap pages for each
> + * populated regions may not naturally algined on page boundary.
> + * So the (present_pages >> 4) heuristic is a tradeoff for that.
> + */
> + if (spanned_pages > present_pages + (present_pages >> 4) &&
> + IS_ENABLED(CONFIG_SPARSEMEM))
> + pages = present_pages;
> +
> + return PAGE_ALIGN(pages * sizeof(struct page)) >> PAGE_SHIFT;
> +}
> +
I spose we should do this, although it makes no difference as the
compiler will inline calc_memmap_size() into its caller:
--- a/mm/page_alloc.c~mm-provide-more-accurate-estimation-of-pages-occupied-by-memmap-fix
+++ a/mm/page_alloc.c
@@ -4526,8 +4526,8 @@ void __init set_pageblock_order(void)
#endif /* CONFIG_HUGETLB_PAGE_SIZE_VARIABLE */
-static unsigned long calc_memmap_size(unsigned long spanned_pages,
- unsigned long present_pages)
+static unsigned long __paginginit calc_memmap_size(unsigned long spanned_pages,
+ unsigned long present_pages)
{
unsigned long pages = spanned_pages;
--
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