From 470f119f012068e5d94458c98dc4eec102f88cd3 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Thu, 5 Nov 2015 18:49:59 -0800 Subject: [PATCH] mm: page migration use migration entry for swapcache too Hitherto page migration has avoided using a migration entry for a swapcache page mapped into userspace, apparently for historical reasons. So any page blessed with swapcache would entail a minor fault when it's next touched, which page migration otherwise tries to avoid. Swapcache in an mlocked area is rare, so won't often matter, but still better fixed. Just rearrange the block in try_to_unmap_one(), to handle TTU_MIGRATION before checking PageAnon, that's all (apart from some reindenting). Well, no, that's not quite all: doesn't this by the way fix a soft_dirty bug, that page migration of a file page was forgetting to transfer the soft_dirty bit? Probably not a serious bug: if I understand correctly, soft_dirty afficionados usually have to handle file pages separately anyway; but we publish the bit in /proc//pagemap on file mappings as well as anonymous, so page migration ought not to perturb it. Signed-off-by: Hugh Dickins Cc: Christoph Lameter Cc: "Kirill A. Shutemov" Cc: Rik van Riel Cc: Vlastimil Babka Cc: Davidlohr Bueso Cc: Oleg Nesterov Cc: Sasha Levin Cc: Dmitry Vyukov Cc: KOSAKI Motohiro Reviewed-by: Cyrill Gorcunov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/rmap.c | 63 ++++++++++++++++++++++++++++++--------------------------------- 1 file changed, 30 insertions(+), 33 deletions(-) diff --git a/mm/rmap.c b/mm/rmap.c index b93fb54..b577fbb 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1379,47 +1379,44 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, dec_mm_counter(mm, MM_ANONPAGES); else dec_mm_counter(mm, MM_FILEPAGES); + } else if (IS_ENABLED(CONFIG_MIGRATION) && (flags & TTU_MIGRATION)) { + swp_entry_t entry; + pte_t swp_pte; + /* + * Store the pfn of the page in a special migration + * pte. do_swap_page() will wait until the migration + * pte is removed and then restart fault handling. + */ + entry = make_migration_entry(page, pte_write(pteval)); + swp_pte = swp_entry_to_pte(entry); + if (pte_soft_dirty(pteval)) + swp_pte = pte_swp_mksoft_dirty(swp_pte); + set_pte_at(mm, address, pte, swp_pte); } else if (PageAnon(page)) { swp_entry_t entry = { .val = page_private(page) }; pte_t swp_pte; - - if (PageSwapCache(page)) { - /* - * Store the swap location in the pte. - * See handle_pte_fault() ... - */ - if (swap_duplicate(entry) < 0) { - set_pte_at(mm, address, pte, pteval); - ret = SWAP_FAIL; - goto out_unmap; - } - if (list_empty(&mm->mmlist)) { - spin_lock(&mmlist_lock); - if (list_empty(&mm->mmlist)) - list_add(&mm->mmlist, &init_mm.mmlist); - spin_unlock(&mmlist_lock); - } - dec_mm_counter(mm, MM_ANONPAGES); - inc_mm_counter(mm, MM_SWAPENTS); - } else if (IS_ENABLED(CONFIG_MIGRATION)) { - /* - * Store the pfn of the page in a special migration - * pte. do_swap_page() will wait until the migration - * pte is removed and then restart fault handling. - */ - BUG_ON(!(flags & TTU_MIGRATION)); - entry = make_migration_entry(page, pte_write(pteval)); + /* + * Store the swap location in the pte. + * See handle_pte_fault() ... + */ + VM_BUG_ON_PAGE(!PageSwapCache(page), page); + if (swap_duplicate(entry) < 0) { + set_pte_at(mm, address, pte, pteval); + ret = SWAP_FAIL; + goto out_unmap; + } + if (list_empty(&mm->mmlist)) { + spin_lock(&mmlist_lock); + if (list_empty(&mm->mmlist)) + list_add(&mm->mmlist, &init_mm.mmlist); + spin_unlock(&mmlist_lock); } + dec_mm_counter(mm, MM_ANONPAGES); + inc_mm_counter(mm, MM_SWAPENTS); swp_pte = swp_entry_to_pte(entry); if (pte_soft_dirty(pteval)) swp_pte = pte_swp_mksoft_dirty(swp_pte); set_pte_at(mm, address, pte, swp_pte); - } else if (IS_ENABLED(CONFIG_MIGRATION) && - (flags & TTU_MIGRATION)) { - /* Establish migration entry for a file page */ - swp_entry_t entry; - entry = make_migration_entry(page, pte_write(pteval)); - set_pte_at(mm, address, pte, swp_entry_to_pte(entry)); } else dec_mm_counter(mm, MM_FILEPAGES); -- 2.7.4