diff options
Diffstat (limited to 'mm/page_isolation.c')
| -rw-r--r-- | mm/page_isolation.c | 671 |
1 files changed, 671 insertions, 0 deletions
diff --git a/mm/page_isolation.c b/mm/page_isolation.c new file mode 100644 index 000000000..47fbc1696 --- /dev/null +++ b/mm/page_isolation.c @@ -0,0 +1,671 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * linux/mm/page_isolation.c + */ + +#include <linux/mm.h> +#include <linux/page-isolation.h> +#include <linux/pageblock-flags.h> +#include <linux/memory.h> +#include <linux/hugetlb.h> +#include <linux/page_owner.h> +#include <linux/migrate.h> +#include "internal.h" + +#define CREATE_TRACE_POINTS +#include <trace/events/page_isolation.h> + +/* + * This function checks whether the range [start_pfn, end_pfn) includes + * unmovable pages or not. The range must fall into a single pageblock and + * consequently belong to a single zone. + * + * PageLRU check without isolation or lru_lock could race so that + * MIGRATE_MOVABLE block might include unmovable pages. And __PageMovable + * check without lock_page also may miss some movable non-lru pages at + * race condition. So you can't expect this function should be exact. + * + * Returns a page without holding a reference. If the caller wants to + * dereference that page (e.g., dumping), it has to make sure that it + * cannot get removed (e.g., via memory unplug) concurrently. + * + */ +static struct page *has_unmovable_pages(unsigned long start_pfn, unsigned long end_pfn, + int migratetype, int flags) +{ + struct page *page = pfn_to_page(start_pfn); + struct zone *zone = page_zone(page); + unsigned long pfn; + + VM_BUG_ON(pageblock_start_pfn(start_pfn) != + pageblock_start_pfn(end_pfn - 1)); + + if (is_migrate_cma_page(page)) { + /* + * CMA allocations (alloc_contig_range) really need to mark + * isolate CMA pageblocks even when they are not movable in fact + * so consider them movable here. + */ + if (is_migrate_cma(migratetype)) + return NULL; + + return page; + } + + for (pfn = start_pfn; pfn < end_pfn; pfn++) { + page = pfn_to_page(pfn); + + /* + * Both, bootmem allocations and memory holes are marked + * PG_reserved and are unmovable. We can even have unmovable + * allocations inside ZONE_MOVABLE, for example when + * specifying "movablecore". + */ + if (PageReserved(page)) + return page; + + /* + * If the zone is movable and we have ruled out all reserved + * pages then it should be reasonably safe to assume the rest + * is movable. + */ + if (zone_idx(zone) == ZONE_MOVABLE) + continue; + + /* + * Hugepages are not in LRU lists, but they're movable. + * THPs are on the LRU, but need to be counted as #small pages. + * We need not scan over tail pages because we don't + * handle each tail page individually in migration. + */ + if (PageHuge(page) || PageTransCompound(page)) { + struct page *head = compound_head(page); + unsigned int skip_pages; + + if (PageHuge(page)) { + if (!hugepage_migration_supported(page_hstate(head))) + return page; + } else if (!PageLRU(head) && !__PageMovable(head)) { + return page; + } + + skip_pages = compound_nr(head) - (page - head); + pfn += skip_pages - 1; + continue; + } + + /* + * We can't use page_count without pin a page + * because another CPU can free compound page. + * This check already skips compound tails of THP + * because their page->_refcount is zero at all time. + */ + if (!page_ref_count(page)) { + if (PageBuddy(page)) + pfn += (1 << buddy_order(page)) - 1; + continue; + } + + /* + * The HWPoisoned page may be not in buddy system, and + * page_count() is not 0. + */ + if ((flags & MEMORY_OFFLINE) && PageHWPoison(page)) + continue; + + /* + * We treat all PageOffline() pages as movable when offlining + * to give drivers a chance to decrement their reference count + * in MEM_GOING_OFFLINE in order to indicate that these pages + * can be offlined as there are no direct references anymore. + * For actually unmovable PageOffline() where the driver does + * not support this, we will fail later when trying to actually + * move these pages that still have a reference count > 0. + * (false negatives in this function only) + */ + if ((flags & MEMORY_OFFLINE) && PageOffline(page)) + continue; + + if (__PageMovable(page) || PageLRU(page)) + continue; + + /* + * If there are RECLAIMABLE pages, we need to check + * it. But now, memory offline itself doesn't call + * shrink_node_slabs() and it still to be fixed. + */ + return page; + } + return NULL; +} + +/* + * This function set pageblock migratetype to isolate if no unmovable page is + * present in [start_pfn, end_pfn). The pageblock must intersect with + * [start_pfn, end_pfn). + */ +static int set_migratetype_isolate(struct page *page, int migratetype, int isol_flags, + unsigned long start_pfn, unsigned long end_pfn) +{ + struct zone *zone = page_zone(page); + struct page *unmovable; + unsigned long flags; + unsigned long check_unmovable_start, check_unmovable_end; + + spin_lock_irqsave(&zone->lock, flags); + + /* + * We assume the caller intended to SET migrate type to isolate. + * If it is already set, then someone else must have raced and + * set it before us. + */ + if (is_migrate_isolate_page(page)) { + spin_unlock_irqrestore(&zone->lock, flags); + return -EBUSY; + } + + /* + * FIXME: Now, memory hotplug doesn't call shrink_slab() by itself. + * We just check MOVABLE pages. + * + * Pass the intersection of [start_pfn, end_pfn) and the page's pageblock + * to avoid redundant checks. + */ + check_unmovable_start = max(page_to_pfn(page), start_pfn); + check_unmovable_end = min(pageblock_end_pfn(page_to_pfn(page)), + end_pfn); + + unmovable = has_unmovable_pages(check_unmovable_start, check_unmovable_end, + migratetype, isol_flags); + if (!unmovable) { + unsigned long nr_pages; + int mt = get_pageblock_migratetype(page); + + set_pageblock_migratetype(page, MIGRATE_ISOLATE); + zone->nr_isolate_pageblock++; + nr_pages = move_freepages_block(zone, page, MIGRATE_ISOLATE, + NULL); + + __mod_zone_freepage_state(zone, -nr_pages, mt); + spin_unlock_irqrestore(&zone->lock, flags); + return 0; + } + + spin_unlock_irqrestore(&zone->lock, flags); + if (isol_flags & REPORT_FAILURE) { + /* + * printk() with zone->lock held will likely trigger a + * lockdep splat, so defer it here. + */ + dump_page(unmovable, "unmovable page"); + } + + return -EBUSY; +} + +static void unset_migratetype_isolate(struct page *page, int migratetype) +{ + struct zone *zone; + unsigned long flags, nr_pages; + bool isolated_page = false; + unsigned int order; + struct page *buddy; + + zone = page_zone(page); + spin_lock_irqsave(&zone->lock, flags); + if (!is_migrate_isolate_page(page)) + goto out; + + /* + * Because freepage with more than pageblock_order on isolated + * pageblock is restricted to merge due to freepage counting problem, + * it is possible that there is free buddy page. + * move_freepages_block() doesn't care of merge so we need other + * approach in order to merge them. Isolation and free will make + * these pages to be merged. + */ + if (PageBuddy(page)) { + order = buddy_order(page); + if (order >= pageblock_order && order < MAX_ORDER - 1) { + buddy = find_buddy_page_pfn(page, page_to_pfn(page), + order, NULL); + if (buddy && !is_migrate_isolate_page(buddy)) { + isolated_page = !!__isolate_free_page(page, order); + /* + * Isolating a free page in an isolated pageblock + * is expected to always work as watermarks don't + * apply here. + */ + VM_WARN_ON(!isolated_page); + } + } + } + + /* + * If we isolate freepage with more than pageblock_order, there + * should be no freepage in the range, so we could avoid costly + * pageblock scanning for freepage moving. + * + * We didn't actually touch any of the isolated pages, so place them + * to the tail of the freelist. This is an optimization for memory + * onlining - just onlined memory won't immediately be considered for + * allocation. + */ + if (!isolated_page) { + nr_pages = move_freepages_block(zone, page, migratetype, NULL); + __mod_zone_freepage_state(zone, nr_pages, migratetype); + } + set_pageblock_migratetype(page, migratetype); + if (isolated_page) + __putback_isolated_page(page, order, migratetype); + zone->nr_isolate_pageblock--; +out: + spin_unlock_irqrestore(&zone->lock, flags); +} + +static inline struct page * +__first_valid_page(unsigned long pfn, unsigned long nr_pages) +{ + int i; + + for (i = 0; i < nr_pages; i++) { + struct page *page; + + page = pfn_to_online_page(pfn + i); + if (!page) + continue; + return page; + } + return NULL; +} + +/** + * isolate_single_pageblock() -- tries to isolate a pageblock that might be + * within a free or in-use page. + * @boundary_pfn: pageblock-aligned pfn that a page might cross + * @flags: isolation flags + * @gfp_flags: GFP flags used for migrating pages + * @isolate_before: isolate the pageblock before the boundary_pfn + * @skip_isolation: the flag to skip the pageblock isolation in second + * isolate_single_pageblock() + * @migratetype: migrate type to set in error recovery. + * + * Free and in-use pages can be as big as MAX_ORDER-1 and contain more than one + * pageblock. When not all pageblocks within a page are isolated at the same + * time, free page accounting can go wrong. For example, in the case of + * MAX_ORDER-1 = pageblock_order + 1, a MAX_ORDER-1 page has two pagelbocks. + * [ MAX_ORDER-1 ] + * [ pageblock0 | pageblock1 ] + * When either pageblock is isolated, if it is a free page, the page is not + * split into separate migratetype lists, which is supposed to; if it is an + * in-use page and freed later, __free_one_page() does not split the free page + * either. The function handles this by splitting the free page or migrating + * the in-use page then splitting the free page. + */ +static int isolate_single_pageblock(unsigned long boundary_pfn, int flags, + gfp_t gfp_flags, bool isolate_before, bool skip_isolation, + int migratetype) +{ + unsigned long start_pfn; + unsigned long isolate_pageblock; + unsigned long pfn; + struct zone *zone; + int ret; + + VM_BUG_ON(!pageblock_aligned(boundary_pfn)); + + if (isolate_before) + isolate_pageblock = boundary_pfn - pageblock_nr_pages; + else + isolate_pageblock = boundary_pfn; + + /* + * scan at the beginning of MAX_ORDER_NR_PAGES aligned range to avoid + * only isolating a subset of pageblocks from a bigger than pageblock + * free or in-use page. Also make sure all to-be-isolated pageblocks + * are within the same zone. + */ + zone = page_zone(pfn_to_page(isolate_pageblock)); + start_pfn = max(ALIGN_DOWN(isolate_pageblock, MAX_ORDER_NR_PAGES), + zone->zone_start_pfn); + + if (skip_isolation) { + int mt __maybe_unused = get_pageblock_migratetype(pfn_to_page(isolate_pageblock)); + + VM_BUG_ON(!is_migrate_isolate(mt)); + } else { + ret = set_migratetype_isolate(pfn_to_page(isolate_pageblock), migratetype, + flags, isolate_pageblock, isolate_pageblock + pageblock_nr_pages); + + if (ret) + return ret; + } + + /* + * Bail out early when the to-be-isolated pageblock does not form + * a free or in-use page across boundary_pfn: + * + * 1. isolate before boundary_pfn: the page after is not online + * 2. isolate after boundary_pfn: the page before is not online + * + * This also ensures correctness. Without it, when isolate after + * boundary_pfn and [start_pfn, boundary_pfn) are not online, + * __first_valid_page() will return unexpected NULL in the for loop + * below. + */ + if (isolate_before) { + if (!pfn_to_online_page(boundary_pfn)) + return 0; + } else { + if (!pfn_to_online_page(boundary_pfn - 1)) + return 0; + } + + for (pfn = start_pfn; pfn < boundary_pfn;) { + struct page *page = __first_valid_page(pfn, boundary_pfn - pfn); + + VM_BUG_ON(!page); + pfn = page_to_pfn(page); + /* + * start_pfn is MAX_ORDER_NR_PAGES aligned, if there is any + * free pages in [start_pfn, boundary_pfn), its head page will + * always be in the range. + */ + if (PageBuddy(page)) { + int order = buddy_order(page); + + if (pfn + (1UL << order) > boundary_pfn) { + /* free page changed before split, check it again */ + if (split_free_page(page, order, boundary_pfn - pfn)) + continue; + } + + pfn += 1UL << order; + continue; + } + /* + * migrate compound pages then let the free page handling code + * above do the rest. If migration is not possible, just fail. + */ + if (PageCompound(page)) { + struct page *head = compound_head(page); + unsigned long head_pfn = page_to_pfn(head); + unsigned long nr_pages = compound_nr(head); + + if (head_pfn + nr_pages <= boundary_pfn) { + pfn = head_pfn + nr_pages; + continue; + } +#if defined CONFIG_COMPACTION || defined CONFIG_CMA + /* + * hugetlb, lru compound (THP), and movable compound pages + * can be migrated. Otherwise, fail the isolation. + */ + if (PageHuge(page) || PageLRU(page) || __PageMovable(page)) { + int order; + unsigned long outer_pfn; + int page_mt = get_pageblock_migratetype(page); + bool isolate_page = !is_migrate_isolate_page(page); + struct compact_control cc = { + .nr_migratepages = 0, + .order = -1, + .zone = page_zone(pfn_to_page(head_pfn)), + .mode = MIGRATE_SYNC, + .ignore_skip_hint = true, + .no_set_skip_hint = true, + .gfp_mask = gfp_flags, + .alloc_contig = true, + }; + INIT_LIST_HEAD(&cc.migratepages); + + /* + * XXX: mark the page as MIGRATE_ISOLATE so that + * no one else can grab the freed page after migration. + * Ideally, the page should be freed as two separate + * pages to be added into separate migratetype free + * lists. + */ + if (isolate_page) { + ret = set_migratetype_isolate(page, page_mt, + flags, head_pfn, head_pfn + nr_pages); + if (ret) + goto failed; + } + + ret = __alloc_contig_migrate_range(&cc, head_pfn, + head_pfn + nr_pages); + + /* + * restore the page's migratetype so that it can + * be split into separate migratetype free lists + * later. + */ + if (isolate_page) + unset_migratetype_isolate(page, page_mt); + + if (ret) + goto failed; + /* + * reset pfn to the head of the free page, so + * that the free page handling code above can split + * the free page to the right migratetype list. + * + * head_pfn is not used here as a hugetlb page order + * can be bigger than MAX_ORDER-1, but after it is + * freed, the free page order is not. Use pfn within + * the range to find the head of the free page. + */ + order = 0; + outer_pfn = pfn; + while (!PageBuddy(pfn_to_page(outer_pfn))) { + /* stop if we cannot find the free page */ + if (++order >= MAX_ORDER) + goto failed; + outer_pfn &= ~0UL << order; + } + pfn = outer_pfn; + continue; + } else +#endif + goto failed; + } + + pfn++; + } + return 0; +failed: + /* restore the original migratetype */ + if (!skip_isolation) + unset_migratetype_isolate(pfn_to_page(isolate_pageblock), migratetype); + return -EBUSY; +} + +/** + * start_isolate_page_range() - make page-allocation-type of range of pages to + * be MIGRATE_ISOLATE. + * @start_pfn: The lower PFN of the range to be isolated. + * @end_pfn: The upper PFN of the range to be isolated. + * @migratetype: Migrate type to set in error recovery. + * @flags: The following flags are allowed (they can be combined in + * a bit mask) + * MEMORY_OFFLINE - isolate to offline (!allocate) memory + * e.g., skip over PageHWPoison() pages + * and PageOffline() pages. + * REPORT_FAILURE - report details about the failure to + * isolate the range + * @gfp_flags: GFP flags used for migrating pages that sit across the + * range boundaries. + * + * Making page-allocation-type to be MIGRATE_ISOLATE means free pages in + * the range will never be allocated. Any free pages and pages freed in the + * future will not be allocated again. If specified range includes migrate types + * other than MOVABLE or CMA, this will fail with -EBUSY. For isolating all + * pages in the range finally, the caller have to free all pages in the range. + * test_page_isolated() can be used for test it. + * + * The function first tries to isolate the pageblocks at the beginning and end + * of the range, since there might be pages across the range boundaries. + * Afterwards, it isolates the rest of the range. + * + * There is no high level synchronization mechanism that prevents two threads + * from trying to isolate overlapping ranges. If this happens, one thread + * will notice pageblocks in the overlapping range already set to isolate. + * This happens in set_migratetype_isolate, and set_migratetype_isolate + * returns an error. We then clean up by restoring the migration type on + * pageblocks we may have modified and return -EBUSY to caller. This + * prevents two threads from simultaneously working on overlapping ranges. + * + * Please note that there is no strong synchronization with the page allocator + * either. Pages might be freed while their page blocks are marked ISOLATED. + * A call to drain_all_pages() after isolation can flush most of them. However + * in some cases pages might still end up on pcp lists and that would allow + * for their allocation even when they are in fact isolated already. Depending + * on how strong of a guarantee the caller needs, zone_pcp_disable/enable() + * might be used to flush and disable pcplist before isolation and enable after + * unisolation. + * + * Return: 0 on success and -EBUSY if any part of range cannot be isolated. + */ +int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn, + int migratetype, int flags, gfp_t gfp_flags) +{ + unsigned long pfn; + struct page *page; + /* isolation is done at page block granularity */ + unsigned long isolate_start = pageblock_start_pfn(start_pfn); + unsigned long isolate_end = pageblock_align(end_pfn); + int ret; + bool skip_isolation = false; + + /* isolate [isolate_start, isolate_start + pageblock_nr_pages) pageblock */ + ret = isolate_single_pageblock(isolate_start, flags, gfp_flags, false, + skip_isolation, migratetype); + if (ret) + return ret; + + if (isolate_start == isolate_end - pageblock_nr_pages) + skip_isolation = true; + + /* isolate [isolate_end - pageblock_nr_pages, isolate_end) pageblock */ + ret = isolate_single_pageblock(isolate_end, flags, gfp_flags, true, + skip_isolation, migratetype); + if (ret) { + unset_migratetype_isolate(pfn_to_page(isolate_start), migratetype); + return ret; + } + + /* skip isolated pageblocks at the beginning and end */ + for (pfn = isolate_start + pageblock_nr_pages; + pfn < isolate_end - pageblock_nr_pages; + pfn += pageblock_nr_pages) { + page = __first_valid_page(pfn, pageblock_nr_pages); + if (page && set_migratetype_isolate(page, migratetype, flags, + start_pfn, end_pfn)) { + undo_isolate_page_range(isolate_start, pfn, migratetype); + unset_migratetype_isolate( + pfn_to_page(isolate_end - pageblock_nr_pages), + migratetype); + return -EBUSY; + } + } + return 0; +} + +/* + * Make isolated pages available again. + */ +void undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn, + int migratetype) +{ + unsigned long pfn; + struct page *page; + unsigned long isolate_start = pageblock_start_pfn(start_pfn); + unsigned long isolate_end = pageblock_align(end_pfn); + + for (pfn = isolate_start; + pfn < isolate_end; + pfn += pageblock_nr_pages) { + page = __first_valid_page(pfn, pageblock_nr_pages); + if (!page || !is_migrate_isolate_page(page)) + continue; + unset_migratetype_isolate(page, migratetype); + } +} +/* + * Test all pages in the range is free(means isolated) or not. + * all pages in [start_pfn...end_pfn) must be in the same zone. + * zone->lock must be held before call this. + * + * Returns the last tested pfn. + */ +static unsigned long +__test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn, + int flags) +{ + struct page *page; + + while (pfn < end_pfn) { + page = pfn_to_page(pfn); + if (PageBuddy(page)) + /* + * If the page is on a free list, it has to be on + * the correct MIGRATE_ISOLATE freelist. There is no + * simple way to verify that as VM_BUG_ON(), though. + */ + pfn += 1 << buddy_order(page); + else if ((flags & MEMORY_OFFLINE) && PageHWPoison(page)) + /* A HWPoisoned page cannot be also PageBuddy */ + pfn++; + else if ((flags & MEMORY_OFFLINE) && PageOffline(page) && + !page_count(page)) + /* + * The responsible driver agreed to skip PageOffline() + * pages when offlining memory by dropping its + * reference in MEM_GOING_OFFLINE. + */ + pfn++; + else + break; + } + + return pfn; +} + +/* Caller should ensure that requested range is in a single zone */ +int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn, + int isol_flags) +{ + unsigned long pfn, flags; + struct page *page; + struct zone *zone; + int ret; + + /* + * Note: pageblock_nr_pages != MAX_ORDER. Then, chunks of free pages + * are not aligned to pageblock_nr_pages. + * Then we just check migratetype first. + */ + for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) { + page = __first_valid_page(pfn, pageblock_nr_pages); + if (page && !is_migrate_isolate_page(page)) + break; + } + page = __first_valid_page(start_pfn, end_pfn - start_pfn); + if ((pfn < end_pfn) || !page) { + ret = -EBUSY; + goto out; + } + + /* Check all pages are free or marked as ISOLATED */ + zone = page_zone(page); + spin_lock_irqsave(&zone->lock, flags); + pfn = __test_page_isolated_in_pageblock(start_pfn, end_pfn, isol_flags); + spin_unlock_irqrestore(&zone->lock, flags); + + ret = pfn < end_pfn ? -EBUSY : 0; + +out: + trace_test_pages_isolated(start_pfn, end_pfn, pfn); + + return ret; +} |