// 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> bool page_is_unmovable(struct zone *zone, struct page *page, enum pb_isolate_mode mode, unsigned long *step) { /* * 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 true; /* * 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) return false; /* * 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) || PageCompound(page)) { struct folio *folio = page_folio(page); if (folio_test_hugetlb(folio)) { struct hstate *h; if (!IS_ENABLED(CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION)) return true; /* * The huge page may be freed so can not * use folio_hstate() directly. */ h = size_to_hstate(folio_size(folio)); if (h && !hugepage_migration_supported(h)) return true; } else if (!folio_test_lru(folio)) { return true; } *step = folio_nr_pages(folio) - folio_page_idx(folio, page); return false; } /* * 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)) *step = (1 << buddy_order(page)); return false; } /* * The HWPoisoned page may be not in buddy system, and * page_count() is not 0. */ if ((mode == PB_ISOLATE_MODE_MEM_OFFLINE) && PageHWPoison(page)) return false; /* * 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 ((mode == PB_ISOLATE_MODE_MEM_OFFLINE) && PageOffline(page)) return false; if (PageLRU(page) || page_has_movable_ops(page)) return false; /* * 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 true; } /* * 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. Similarly, pages * with movable_ops can only be identified some time after they were * allocated. 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, enum pb_isolate_mode mode) { struct page *page = pfn_to_page(start_pfn); struct zone *zone = page_zone(page); 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 (mode == PB_ISOLATE_MODE_CMA_ALLOC) return NULL; return page; } while (start_pfn < end_pfn) { unsigned long step = 1; page = pfn_to_page(start_pfn); if (page_is_unmovable(zone, page, mode, &step)) return page; start_pfn += step; } 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, enum pb_isolate_mode mode, 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; if (PageUnaccepted(page)) accept_page(page); 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, mode); if (!unmovable) { if (!pageblock_isolate_and_move_free_pages(zone, page)) { spin_unlock_irqrestore(&zone->lock, flags); return -EBUSY; } zone->nr_isolate_pageblock++; spin_unlock_irqrestore(&zone->lock, flags); return 0; } spin_unlock_irqrestore(&zone->lock, flags); if (mode == PB_ISOLATE_MODE_MEM_OFFLINE) { /* * 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) { struct zone *zone; unsigned long flags; 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_PAGE_ORDER) { 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) { /* * Isolating this block already succeeded, so this * should not fail on zone boundaries. */ WARN_ON_ONCE(!pageblock_unisolate_and_move_free_pages(zone, page)); } else { clear_pageblock_isolate(page); __putback_isolated_page(page, order, get_pageblock_migratetype(page)); } 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 * @mode: isolation mode * @isolate_before: isolate the pageblock before the boundary_pfn * @skip_isolation: the flag to skip the pageblock isolation in second * isolate_single_pageblock() * * Free and in-use pages can be as big as MAX_PAGE_ORDER 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_PAGE_ORDER = pageblock_order + 1, a MAX_PAGE_ORDER page has two * pageblocks. * [ MAX_PAGE_ORDER ] * [ 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, enum pb_isolate_mode mode, bool isolate_before, bool skip_isolation) { 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) { VM_BUG_ON(!get_pageblock_isolate(pfn_to_page(isolate_pageblock))); } else { ret = set_migratetype_isolate(pfn_to_page(isolate_pageblock), mode, 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); if (PageUnaccepted(page)) { pfn += MAX_ORDER_NR_PAGES; continue; } if (PageBuddy(page)) { int order = buddy_order(page); /* pageblock_isolate_and_move_free_pages() handled this */ VM_WARN_ON_ONCE(pfn + (1 << order) > boundary_pfn); pfn += 1UL << order; continue; } /* * If a compound page is straddling our block, attempt * to migrate it out of the way. * * We don't have to worry about this creating a large * free page that straddles into our block: gigantic * pages are freed as order-0 chunks, and LRU pages * (currently) do not exceed pageblock_order. * * The block of interest has already been marked * MIGRATE_ISOLATE above, so when migration is done it * will free its pages onto the correct freelists. */ 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 || PageHuge(page)) { pfn = head_pfn + nr_pages; continue; } /* * These pages are movable too, but they're * not expected to exceed pageblock_order. * * Let us know when they do, so we can add * proper free and split handling for them. */ VM_WARN_ON_ONCE_PAGE(PageLRU(page), page); VM_WARN_ON_ONCE_PAGE(page_has_movable_ops(page), page); goto failed; } pfn++; } return 0; failed: /* restore the original migratetype */ if (!skip_isolation) unset_migratetype_isolate(pfn_to_page(isolate_pageblock)); return -EBUSY; } /** * start_isolate_page_range() - mark page range MIGRATE_ISOLATE * @start_pfn: The first PFN of the range to be isolated. * @end_pfn: The last PFN of the range to be isolated. * @mode: isolation mode * * 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, enum pb_isolate_mode mode) { 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, mode, false, skip_isolation); 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, mode, true, skip_isolation); if (ret) { unset_migratetype_isolate(pfn_to_page(isolate_start)); 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, mode, start_pfn, end_pfn)) { undo_isolate_page_range(isolate_start, pfn); unset_migratetype_isolate( pfn_to_page(isolate_end - pageblock_nr_pages)); return -EBUSY; } } return 0; } /** * undo_isolate_page_range - undo effects of start_isolate_page_range() * @start_pfn: The first PFN of the isolated range * @end_pfn: The last PFN of the isolated range * * This finds and unsets every MIGRATE_ISOLATE page block in the given range */ void undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn) { 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); } } /* * 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, enum pb_isolate_mode mode) { 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 ((mode == PB_ISOLATE_MODE_MEM_OFFLINE) && PageHWPoison(page)) /* A HWPoisoned page cannot be also PageBuddy */ pfn++; else if ((mode == PB_ISOLATE_MODE_MEM_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; } /** * test_pages_isolated - check if pageblocks in range are isolated * @start_pfn: The first PFN of the isolated range * @end_pfn: The first PFN *after* the isolated range * @mode: Testing mode * * This tests if all in the specified range are free. * * If %PB_ISOLATE_MODE_MEM_OFFLINE specified in @mode, it will consider * poisoned and offlined pages free as well. * * Caller must ensure the requested range doesn't span zones. * * Returns 0 if true, -EBUSY if one or more pages are in use. */ int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn, enum pb_isolate_mode mode) { unsigned long pfn, flags; struct page *page; struct zone *zone; int ret; /* * Due to the deferred freeing of hugetlb folios, the hugepage folios may * not immediately release to the buddy system. This can cause PageBuddy() * to fail in __test_page_isolated_in_pageblock(). To ensure that the * hugetlb folios are properly released back to the buddy system, we * invoke the wait_for_freed_hugetlb_folios() function to wait for the * release to complete. */ wait_for_freed_hugetlb_folios(); /* * Note: pageblock_nr_pages != MAX_PAGE_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, mode); spin_unlock_irqrestore(&zone->lock, flags); ret = pfn < end_pfn ? -EBUSY : 0; out: trace_test_pages_isolated(start_pfn, end_pfn, pfn); return ret; }
