linux-kernel - [PATCH 01/25] mm/um: Fix extra accounting for page fault retries

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Date:   Mon, 15 Jun 2020 18:15:43 -0400
From:   Peter Xu <peterx@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Gerald Schaefer <gerald.schaefer@...ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>, peterx@...hat.com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        linux-um@...ts.infradead.org
Subject: [PATCH 01/25] mm/um: Fix extra accounting for page fault retries

When page fault retried, we should only do the accounting once rather than once
for each page fault retry.

CC: Jeff Dike <jdike@...toit.com>
CC: Richard Weinberger <richard@....at>
CC: Anton Ivanov <anton.ivanov@...bridgegreys.com>
CC: linux-um@...ts.infradead.org
Signed-off-by: Peter Xu <peterx@...hat.com>
---
 arch/um/kernel/trap.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index 8f18cf56b3dd..d162168490d1 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -34,6 +34,7 @@ int handle_page_fault(unsigned long address, unsigned long ip,
 	pte_t *pte;
 	int err = -EFAULT;
 	unsigned int flags = FAULT_FLAG_DEFAULT;
+	vm_fault_t fault, major = 0;
 
 	*code_out = SEGV_MAPERR;
 
@@ -73,9 +74,8 @@ int handle_page_fault(unsigned long address, unsigned long ip,
 	}
 
 	do {
-		vm_fault_t fault;
-
 		fault = handle_mm_fault(vma, address, flags);
+		major |= fault & VM_FAULT_MAJOR;
 
 		if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
 			goto out_nosemaphore;
@@ -92,10 +92,6 @@ int handle_page_fault(unsigned long address, unsigned long ip,
 			BUG();
 		}
 		if (flags & FAULT_FLAG_ALLOW_RETRY) {
-			if (fault & VM_FAULT_MAJOR)
-				current->maj_flt++;
-			else
-				current->min_flt++;
 			if (fault & VM_FAULT_RETRY) {
 				flags |= FAULT_FLAG_TRIED;
 
@@ -103,6 +99,11 @@ int handle_page_fault(unsigned long address, unsigned long ip,
 			}
 		}
 
+		if (major)
+			current->maj_flt++;
+		else
+			current->min_flt++;
+
 		pgd = pgd_offset(mm, address);
 		p4d = p4d_offset(pgd, address);
 		pud = pud_offset(p4d, address);
-- 
2.26.2