Re: [RFT PATCH v2 4/5] mm: provide more accurate estimation of pages occupied by memmap
From: Andrew Morton <akpm@linux-foundation.org>
Date: 2012-11-28 23:52:24
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On Wed, 21 Nov 2012 23:09:46 +0800 Jiang Liu [off-list ref] 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"?
quoted hunk ↗ jump to hunk
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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