From 5c755e9fd813810680abd56ec09a5f90143e815b Mon Sep 17 00:00:00 2001 From: Badari Pulavarty Date: Wed, 23 Jul 2008 21:28:19 -0700 Subject: memory-hotplug: add sysfs removable attribute for hotplug memory remove Memory may be hot-removed on a per-memory-block basis, particularly on POWER where the SPARSEMEM section size often matches the memory-block size. A user-level agent must be able to identify which sections of memory are likely to be removable before attempting the potentially expensive operation. This patch adds a file called "removable" to the memory directory in sysfs to help such an agent. In this patch, a memory block is considered removable if; o It contains only MOVABLE pageblocks o It contains only pageblocks with free pages regardless of pageblock type On the other hand, a memory block starting with a PageReserved() page will never be considered removable. Without this patch, the user-agent is forced to choose a memory block to remove randomly. Sample output of the sysfs files: ./memory/memory0/removable: 0 ./memory/memory1/removable: 0 ./memory/memory2/removable: 0 ./memory/memory3/removable: 0 ./memory/memory4/removable: 0 ./memory/memory5/removable: 0 ./memory/memory6/removable: 0 ./memory/memory7/removable: 1 ./memory/memory8/removable: 0 ./memory/memory9/removable: 0 ./memory/memory10/removable: 0 ./memory/memory11/removable: 0 ./memory/memory12/removable: 0 ./memory/memory13/removable: 0 ./memory/memory14/removable: 0 ./memory/memory15/removable: 0 ./memory/memory16/removable: 0 ./memory/memory17/removable: 1 ./memory/memory18/removable: 1 ./memory/memory19/removable: 1 ./memory/memory20/removable: 1 ./memory/memory21/removable: 1 ./memory/memory22/removable: 1 Signed-off-by: Badari Pulavarty Signed-off-by: Mel Gorman Acked-by: KAMEZAWA Hiroyuki Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memory_hotplug.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 60 insertions(+) (limited to 'mm') diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 93aba78dc8b..89fee2dcb03 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -522,6 +522,66 @@ error: EXPORT_SYMBOL_GPL(add_memory); #ifdef CONFIG_MEMORY_HOTREMOVE +/* + * A free page on the buddy free lists (not the per-cpu lists) has PageBuddy + * set and the size of the free page is given by page_order(). Using this, + * the function determines if the pageblock contains only free pages. + * Due to buddy contraints, a free page at least the size of a pageblock will + * be located at the start of the pageblock + */ +static inline int pageblock_free(struct page *page) +{ + return PageBuddy(page) && page_order(page) >= pageblock_order; +} + +/* Return the start of the next active pageblock after a given page */ +static struct page *next_active_pageblock(struct page *page) +{ + int pageblocks_stride; + + /* Ensure the starting page is pageblock-aligned */ + BUG_ON(page_to_pfn(page) & (pageblock_nr_pages - 1)); + + /* Move forward by at least 1 * pageblock_nr_pages */ + pageblocks_stride = 1; + + /* If the entire pageblock is free, move to the end of free page */ + if (pageblock_free(page)) + pageblocks_stride += page_order(page) - pageblock_order; + + return page + (pageblocks_stride * pageblock_nr_pages); +} + +/* Checks if this range of memory is likely to be hot-removable. */ +int is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages) +{ + int type; + struct page *page = pfn_to_page(start_pfn); + struct page *end_page = page + nr_pages; + + /* Check the starting page of each pageblock within the range */ + for (; page < end_page; page = next_active_pageblock(page)) { + type = get_pageblock_migratetype(page); + + /* + * A pageblock containing MOVABLE or free pages is considered + * removable + */ + if (type != MIGRATE_MOVABLE && !pageblock_free(page)) + return 0; + + /* + * A pageblock starting with a PageReserved page is not + * considered removable. + */ + if (PageReserved(page)) + return 0; + } + + /* All pageblocks in the memory block are likely to be hot-removable */ + return 1; +} + /* * Confirm all pages in a range [start, end) is belongs to the same zone. */ -- cgit v1.2.2