On Thu, Dec 22, 2016 at 11:52:03PM +0900, Minchan Kim wrote:

Hello,

On Thu, Dec 22, 2016 at 11:17:13AM +0300, Kirill A. Shutemov wrote:

< snip >

quoted

quoted

diff --git a/mm/memory.c b/mm/memory.c
index 36c774f..7408ddc 100644
--- a/mm/memory.c
+++ b/mm/memory.c

@@ -3637,18 +3637,20 @@ static int __handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
 			if (pmd_protnone(orig_pmd) && vma_is_accessible(vma))
 				return do_huge_pmd_numa_page(&vmf, orig_pmd);
 
-			if ((vmf.flags & FAULT_FLAG_WRITE) &&
-					!pmd_write(orig_pmd)) {
-				ret = wp_huge_pmd(&vmf, orig_pmd);
-				if (!(ret & VM_FAULT_FALLBACK))
+			if (vmf.flags & FAULT_FLAG_WRITE) {
+				if (!pmd_write(orig_pmd)) {
+					ret = wp_huge_pmd(&vmf, orig_pmd);
+					if (ret == VM_FAULT_FALLBACK)

In theory, more than one flag can be set and it would lead to
false-negative. Bit check was the right thing.

And I don't understand why do you need to change code in
__handle_mm_fault() at all.
From what I see change to huge_pmd_set_accessed() should be enough.

Yeb. Thanks for the review. Here v2 goes.

From b3ec95c0df91ad113525968a4a6b53030fd0b48d Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Thu, 22 Dec 2016 23:43:49 +0900
Subject: [PATCH v2] mm: pmd dirty emulation in page fault handler

Andreas reported [1] made a test in jemalloc hang in THP mode in arm64.
http://lkml.kernel.org/r/mvmmvfy37g1.fsf at hawking.suse.de

The problem is page fault handler supports only accessed flag emulation
for THP page of SW-dirty/accessed architecture.

This patch enables dirty-bit emulation for those architectures.
Without it, MADV_FREE makes application hang by repeated fault forever.

[1] b8d3c4c3009d, mm/huge_memory.c: don't split THP page when MADV_FREE syscall is called

Cc: Jason Evans <redacted>
Cc: Kirill A. Shutemov <redacted>
Cc: Will Deacon <redacted>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-arch at vger.kernel.org
Cc: linux-arm-kernel at lists.infradead.org
Cc: <redacted> [4.5+]
Fixes: b8d3c4c3009d ("mm/huge_memory.c: don't split THP page when MADV_FREE syscall is called")
Reported-by: Andreas Schwab <redacted>
Signed-off-by: Minchan Kim <minchan@kernel.org>

Acked-by: Kirill A. Shutemov <redacted>

-- 
 Kirill A. Shutemov