mm: provide more accurate estimation of pages occupied by memmap
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. [akpm@linux-foundation.org: mark calc_memmap_size __paging_init] Signed-off-by: Jiang Liu <jiang.liu@huawei.com> Cc: Wen Congyang <wency@cn.fujitsu.com> Cc: David Rientjes <rientjes@google.com> Cc: Maciej Rutecki <maciej.rutecki@gmail.com> Cc: Chris Clayton <chris2553@googlemail.com> Cc: "Rafael J . Wysocki" <rjw@sisk.pl> Cc: Mel Gorman <mgorman@suse.de> Cc: Minchan Kim <minchan@kernel.org> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Michal Hocko <mhocko@suse.cz> Tested-by: Jianguo Wu <wujianguo@huawei.com> Cc: Dave Hansen <dave@linux.vnet.ibm.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -4489,6 +4489,26 @@ void __init set_pageblock_order(void)
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#endif /* CONFIG_HUGETLB_PAGE_SIZE_VARIABLE */
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#endif /* CONFIG_HUGETLB_PAGE_SIZE_VARIABLE */
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static unsigned long __paginginit calc_memmap_size(unsigned long spanned_pages,
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unsigned long present_pages)
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{
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unsigned long pages = spanned_pages;
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/*
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* Provide a more accurate estimation if there are holes within
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* the zone and SPARSEMEM is in use. If there are holes within the
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* zone, each populated memory region may cost us one or two extra
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* memmap pages due to alignment because memmap pages for each
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* populated regions may not naturally algined on page boundary.
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* So the (present_pages >> 4) heuristic is a tradeoff for that.
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*/
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if (spanned_pages > present_pages + (present_pages >> 4) &&
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IS_ENABLED(CONFIG_SPARSEMEM))
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pages = present_pages;
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return PAGE_ALIGN(pages * sizeof(struct page)) >> PAGE_SHIFT;
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}
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/*
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/*
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* Set up the zone data structures:
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* Set up the zone data structures:
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* - mark all pages reserved
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* - mark all pages reserved
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@ -4523,8 +4543,7 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
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* is used by this zone for memmap. This affects the watermark
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* is used by this zone for memmap. This affects the watermark
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* and per-cpu initialisations
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* and per-cpu initialisations
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*/
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*/
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memmap_pages =
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memmap_pages = calc_memmap_size(size, realsize);
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PAGE_ALIGN(size * sizeof(struct page)) >> PAGE_SHIFT;
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if (freesize >= memmap_pages) {
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if (freesize >= memmap_pages) {
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freesize -= memmap_pages;
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freesize -= memmap_pages;
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if (memmap_pages)
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if (memmap_pages)
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@ -4545,6 +4564,9 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
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if (!is_highmem_idx(j))
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if (!is_highmem_idx(j))
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nr_kernel_pages += freesize;
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nr_kernel_pages += freesize;
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/* Charge for highmem memmap if there are enough kernel pages */
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else if (nr_kernel_pages > memmap_pages * 2)
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nr_kernel_pages -= memmap_pages;
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nr_all_pages += freesize;
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nr_all_pages += freesize;
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zone->spanned_pages = size;
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zone->spanned_pages = size;
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