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*参照元 [#v3a8a1fb] #backlinks *説明 [#a7fbdb14] -パス: [[linux-4.4.1/mm/compaction.c]] -FIXME: これは何？ --説明 **引数 [#x9175fa9] -struct compact_control *cc -- --[[linux-4.4.1/compact_control]] -unsigned long low_pfn -- -unsigned long end_pfn -- -isolate_mode_t isolate_mode -- --[[linux-4.4.1/isolate_mode_t]] **返り値 [#wddf765a] -unsigned long -- **参考 [#d55440ec] *実装 [#p25b927c] /** * isolate_migratepages_block() - isolate all migrate-able pages within * a single pageblock * @cc: Compaction control structure. * @low_pfn: The first PFN to isolate * @end_pfn: The one-past-the-last PFN to isolate, within same pageblock * @isolate_mode: Isolation mode to be used. * * Isolate all pages that can be migrated from the range specified by * [low_pfn, end_pfn). The range is expected to be within same pageblock. * Returns zero if there is a fatal signal pending, otherwise PFN of the * first page that was not scanned (which may be both less, equal to or more * than end_pfn). * * The pages are isolated on cc->migratepages list (not required to be empty), * and cc->nr_migratepages is updated accordingly. The cc->migrate_pfn field * is neither read nor updated. */ static unsigned long isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, unsigned long end_pfn, isolate_mode_t isolate_mode) { struct zone *zone = cc->zone; unsigned long nr_scanned = 0, nr_isolated = 0; struct list_head *migratelist = &cc->migratepages; struct lruvec *lruvec; unsigned long flags = 0; bool locked = false; struct page *page = NULL, *valid_page = NULL; unsigned long start_pfn = low_pfn; - --[[linux-4.4.1/zone]] --[[linux-4.4.1/list_head]] --[[linux-4.4.1/lruvec]] --[[linux-4.4.1/page]] /* * Ensure that there are not too many pages isolated from the LRU * list by either parallel reclaimers or compaction. If there are, * delay for some time until fewer pages are isolated */ while (unlikely(too_many_isolated(zone))) { /* async migration should just abort */ if (cc->mode == MIGRATE_ASYNC) return 0; congestion_wait(BLK_RW_ASYNC, HZ/10); if (fatal_signal_pending(current)) return 0; } - --[[linux-4.4.1/unlikely()]] --[[linux-4.4.1/too_many_isolated()]] --[[linux-4.4.1/congestion_wait()]] --[[linux-4.4.1/fatal_signal_pending()]] if (compact_should_abort(cc)) return 0; - --[[linux-4.4.1/compact_should_abort()]] /* Time to isolate some pages for migration */ for (; low_pfn < end_pfn; low_pfn++) { bool is_lru; /* * Periodically drop the lock (if held) regardless of its * contention, to give chance to IRQs. Abort async compaction * if contended. */ if (!(low_pfn % SWAP_CLUSTER_MAX) && compact_unlock_should_abort(&zone->lru_lock, flags, &locked, cc)) break; - --[[linux-4.4.1/compact_unlock_should_abort()]] if (!pfn_valid_within(low_pfn)) continue; nr_scanned++; - --[[linux-4.4.1/pfn_valid_within()]] page = pfn_to_page(low_pfn); if (!valid_page) valid_page = page; - --[[linux-4.4.1/pfn_to_page()]] /* * Skip if free. We read page order here without zone lock * which is generally unsafe, but the race window is small and * the worst thing that can happen is that we skip some * potential isolation targets. */ if (PageBuddy(page)) { unsigned long freepage_order = page_order_unsafe(page); /* * Without lock, we cannot be sure that what we got is * a valid page order. Consider only values in the * valid order range to prevent low_pfn overflow. */ if (freepage_order > 0 && freepage_order < MAX_ORDER) low_pfn += (1UL << freepage_order) - 1; continue; } - --[[linux-4.4.1/PageBuddy()]] --[[linux-4.4.1/page_order_unsafe()]] /* * Check may be lockless but that's ok as we recheck later. * It's possible to migrate LRU pages and balloon pages * Skip any other type of page */ is_lru = PageLRU(page); if (!is_lru) { if (unlikely(balloon_page_movable(page))) { if (balloon_page_isolate(page)) { /* Successfully isolated */ goto isolate_success; } } } - --[[linux-4.4.1/PageLRU()]] --[[linux-4.4.1/balloon_page_movable()]] --[[linux-4.4.1/balloon_page_isolate()]] /* * Regardless of being on LRU, compound pages such as THP and * hugetlbfs are not to be compacted. We can potentially save * a lot of iterations if we skip them at once. The check is * racy, but we can consider only valid values and the only * danger is skipping too much. */ if (PageCompound(page)) { unsigned int comp_order = compound_order(page); if (likely(comp_order < MAX_ORDER)) low_pfn += (1UL << comp_order) - 1; continue; } - --[[linux-4.4.1/PageCompound()]] --[[linux-4.4.1/compound_order()]] if (!is_lru) continue; /* * Migration will fail if an anonymous page is pinned in memory, * so avoid taking lru_lock and isolating it unnecessarily in an * admittedly racy check. */ if (!page_mapping(page) && page_count(page) > page_mapcount(page)) continue; - --[[linux-4.4.1/page_mapping()]] --[[linux-4.4.1/page_count()]] --[[linux-4.4.1/page_mapcount()]] /* If we already hold the lock, we can skip some rechecking */ if (!locked) { locked = compact_trylock_irqsave(&zone->lru_lock, &flags, cc); if (!locked) break; /* Recheck PageLRU and PageCompound under lock */ if (!PageLRU(page)) continue; /* * Page become compound since the non-locked check, * and it's on LRU. It can only be a THP so the order * is safe to read and it's 0 for tail pages. */ if (unlikely(PageCompound(page))) { low_pfn += (1UL << compound_order(page)) - 1; continue; } } - --[[linux-4.4.1/compact_trylock_irqsave()]] --[[linux-4.4.1/PageLRU()]] --[[linux-4.4.1/PageCompound()]] --[[linux-4.4.1/compound_order()]] lruvec = mem_cgroup_page_lruvec(page, zone); - --[[linux-4.4.1/mem_cgroup_page_lruvec()]] /* Try isolate the page */ if (__isolate_lru_page(page, isolate_mode) != 0) continue; VM_BUG_ON_PAGE(PageCompound(page), page); - --[[linux-4.4.1/__isolate_lru_page()]] --[[linux-4.4.1/VM_BUG_ON_PAGE()]] --[[linux-4.4.1/PageCompound()]] /* Successfully isolated */ del_page_from_lru_list(page, lruvec, page_lru(page)); - --[[linux-4.4.1/del_page_from_lru_list()]] --[[linux-4.4.1/page_lru()]] isolate_success: list_add(&page->lru, migratelist); cc->nr_migratepages++; nr_isolated++; - --[[linux-4.4.1/list_add()]] /* Avoid isolating too much */ if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) { ++low_pfn; break; } } /* * The PageBuddy() check could have potentially brought us outside * the range to be scanned. */ if (unlikely(low_pfn > end_pfn)) low_pfn = end_pfn; if (locked) spin_unlock_irqrestore(&zone->lru_lock, flags); - --[[linux-4.4.1/spin_unlock_irqrestore()]] /* * Update the pageblock-skip information and cached scanner pfn, * if the whole pageblock was scanned without isolating any page. */ if (low_pfn == end_pfn) update_pageblock_skip(cc, valid_page, nr_isolated, true); trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn, nr_scanned, nr_isolated); count_compact_events(COMPACTMIGRATE_SCANNED, nr_scanned); if (nr_isolated) count_compact_events(COMPACTISOLATED, nr_isolated); - --[[linux-4.4.1/update_pageblock_skip()]] --[[linux-4.4.1/trace_mm_compaction_isolate_migratepages()]] --[[linux-4.4.1/count_compact_events()]] return low_pfn; } *コメント [#w5343847]
