From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-x22d.google.com (mail-pa0-x22d.google.com [IPv6:2607:f8b0:400e:c03::22d]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 51DBA1A0908 for ; Sun, 10 Jan 2016 11:59:48 +1100 (AEDT) Received: by mail-pa0-x22d.google.com with SMTP id yy13so209749568pab.3 for ; Sat, 09 Jan 2016 16:59:48 -0800 (PST) Date: Sat, 9 Jan 2016 16:59:42 -0800 (PST) From: Hugh Dickins To: Andrew Morton cc: Cyrill Gorcunov , Laurent Dufour , Michael Ellerman , "Aneesh Kumar K.V" , Martin Schwidefsky , linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org Subject: [PATCH next] mm: make swapoff more robust against soft dirty In-Reply-To: Message-ID: References: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Both s390 and powerpc have hit the issue of swapoff hanging, when CONFIG_HAVE_ARCH_SOFT_DIRTY and CONFIG_MEM_SOFT_DIRTY ifdefs were not quite as x86_64 had them. I think it would be much clearer if HAVE_ARCH_SOFT_DIRTY was just a Kconfig option set by architectures to determine whether the MEM_SOFT_DIRTY option should be offered, and the actual code depend upon CONFIG_MEM_SOFT_DIRTY alone. But won't embark on that change myself: instead make swapoff more robust, by using pte_swp_clear_soft_dirty() on each pte it encounters, without an explicit #ifdef CONFIG_MEM_SOFT_DIRTY. That being a no-op, whether the bit in question is defined as 0 or the asm-generic fallback is used, unless soft dirty is fully turned on. Why "maybe" in maybe_same_pte()? Rename it pte_same_as_swp(). Signed-off-by: Hugh Dickins --- mm/swapfile.c | 18 ++++-------------- 1 file changed, 4 insertions(+), 14 deletions(-) --- 4.4-next/mm/swapfile.c 2016-01-06 11:54:46.327006983 -0800 +++ linux/mm/swapfile.c 2016-01-09 13:39:19.632872694 -0800 @@ -1109,19 +1109,9 @@ unsigned int count_swap_pages(int type, } #endif /* CONFIG_HIBERNATION */ -static inline int maybe_same_pte(pte_t pte, pte_t swp_pte) +static inline int pte_same_as_swp(pte_t pte, pte_t swp_pte) { -#ifdef CONFIG_MEM_SOFT_DIRTY - /* - * When pte keeps soft dirty bit the pte generated - * from swap entry does not has it, still it's same - * pte from logical point of view. - */ - pte_t swp_pte_dirty = pte_swp_mksoft_dirty(swp_pte); - return pte_same(pte, swp_pte) || pte_same(pte, swp_pte_dirty); -#else - return pte_same(pte, swp_pte); -#endif + return pte_same(pte_swp_clear_soft_dirty(pte), swp_pte); } /* @@ -1150,7 +1140,7 @@ static int unuse_pte(struct vm_area_stru } pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); - if (unlikely(!maybe_same_pte(*pte, swp_entry_to_pte(entry)))) { + if (unlikely(!pte_same_as_swp(*pte, swp_entry_to_pte(entry)))) { mem_cgroup_cancel_charge(page, memcg, false); ret = 0; goto out; @@ -1208,7 +1198,7 @@ static int unuse_pte_range(struct vm_are * swapoff spends a _lot_ of time in this loop! * Test inline before going to call unuse_pte. */ - if (unlikely(maybe_same_pte(*pte, swp_pte))) { + if (unlikely(pte_same_as_swp(*pte, swp_pte))) { pte_unmap(pte); ret = unuse_pte(vma, pmd, addr, entry, page); if (ret)