[164/165] mm: clean up the last pieces of page fault accountings

Commit Message

Andrew Morton Aug. 12, 2020, 1:38 a.m. UTC

From: Peter Xu <[e-mail]>
Subject: mm: clean up the last pieces of page fault accountings

Here're the last pieces of page fault accounting that were still done
outside handle_mm_fault() where we still have regs==NULL when calling
handle_mm_fault():

arch/powerpc/mm/copro_fault.c:   copro_handle_mm_fault
arch/sparc/mm/fault_32.c:        force_user_fault
arch/um/kernel/trap.c:           handle_page_fault
mm/gup.c:                        faultin_page
                                 fixup_user_fault
mm/hmm.c:                        hmm_vma_fault
mm/ksm.c:                        break_ksm

Some of them has the issue of duplicated accounting for page fault
retries.  Some of them didn't do the accounting at all.

This patch cleans all these up by letting handle_mm_fault() to do per-task
page fault accounting even if regs==NULL (though we'll still skip the perf
event accountings).  With that, we can safely remove all the outliers now.

There's another functional change in that now we account the page faults
to the caller of gup, rather than the task_struct that passed into the gup
code.  More information of this can be found at [1].

After this patch, below things should never be touched again outside
handle_mm_fault():

  - task_struct.[maj|min]_flt
  - PERF_COUNT_SW_PAGE_FAULTS_[MAJ|MIN]

[1] https://lore.kernel.org/lkml/CAHk-=[e-mail]/

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Peter Xu <[e-mail]>
Cc: Albert Ou <[e-mail]>
Cc: Alexander Gordeev <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Benjamin Herrenschmidt <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Brian Cain <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Christian Borntraeger <[e-mail]>
Cc: Chris Zankel <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Cc: David S. Miller <[e-mail]>
Cc: Geert Uytterhoeven <[e-mail]>
Cc: Gerald Schaefer <[e-mail]>
Cc: Greentime Hu <[e-mail]>
Cc: Guo Ren <[e-mail]>
Cc: Heiko Carstens <[e-mail]>
Cc: Helge Deller <[e-mail]>
Cc: H. Peter Anvin <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Ivan Kokshaysky <[e-mail]>
Cc: James E.J. Bottomley <[e-mail]>
Cc: John Hubbard <[e-mail]>
Cc: Jonas Bonn <[e-mail]>
Cc: Ley Foon Tan <[e-mail]>
Cc: "Luck, Tony" <[e-mail]>
Cc: Matt Turner <[e-mail]>
Cc: Max Filippov <[e-mail]>
Cc: Michael Ellerman <[e-mail]>
Cc: Michal Simek <[e-mail]>
Cc: Nick Hu <[e-mail]>
Cc: Palmer Dabbelt <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Paul Walmsley <[e-mail]>
Cc: Pekka Enberg <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Richard Henderson <[e-mail]>
Cc: Rich Felker <[e-mail]>
Cc: Russell King <[e-mail]>
Cc: Stafford Horne <[e-mail]>
Cc: Stefan Kristiansson <[e-mail]>
Cc: Thomas Bogendoerfer <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Vasily Gorbik <[e-mail]>
Cc: Vincent Chen <[e-mail]>
Cc: Vineet Gupta <[e-mail]>
Cc: Will Deacon <[e-mail]>
Cc: Yoshinori Sato <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 arch/powerpc/mm/copro_fault.c |    5 -----
 arch/um/kernel/trap.c         |    4 ----
 mm/gup.c                      |   13 -------------
 mm/memory.c                   |   17 ++++++++++-------
 4 files changed, 10 insertions(+), 29 deletions(-)

Patch

--- a/arch/powerpc/mm/copro_fault.c~mm-clean-up-the-last-pieces-of-page-fault-accountings
+++ a/arch/powerpc/mm/copro_fault.c
@@ -76,11 +76,6 @@  int copro_handle_mm_fault(struct mm_stru
 		BUG();
 	}
 
-	if (*flt & VM_FAULT_MAJOR)
-		current->maj_flt++;
-	else
-		current->min_flt++;
-
 out_unlock:
 	mmap_read_unlock(mm);
 	return ret;
--- a/arch/um/kernel/trap.c~mm-clean-up-the-last-pieces-of-page-fault-accountings
+++ a/arch/um/kernel/trap.c
@@ -88,10 +88,6 @@  good_area:
 			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;
 
--- a/mm/gup.c~mm-clean-up-the-last-pieces-of-page-fault-accountings
+++ a/mm/gup.c
@@ -893,13 +893,6 @@  static int faultin_page(struct task_stru
 		BUG();
 	}
 
-	if (tsk) {
-		if (ret & VM_FAULT_MAJOR)
-			tsk->maj_flt++;
-		else
-			tsk->min_flt++;
-	}
-
 	if (ret & VM_FAULT_RETRY) {
 		if (locked && !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
 			*locked = 0;
@@ -1255,12 +1248,6 @@  retry:
 		goto retry;
 	}
 
-	if (tsk) {
-		if (major)
-			tsk->maj_flt++;
-		else
-			tsk->min_flt++;
-	}
 	return 0;
 }
 EXPORT_SYMBOL_GPL(fixup_user_fault);
--- a/mm/memory.c~mm-clean-up-the-last-pieces-of-page-fault-accountings
+++ a/mm/memory.c
@@ -4400,20 +4400,23 @@  static inline void mm_account_fault(stru
 	 */
 	major = (ret & VM_FAULT_MAJOR) || (flags & FAULT_FLAG_TRIED);
 
+	if (major)
+		current->maj_flt++;
+	else
+		current->min_flt++;
+
 	/*
-	 * If the fault is done for GUP, regs will be NULL, and we will skip
-	 * the fault accounting.
+	 * If the fault is done for GUP, regs will be NULL.  We only do the
+	 * accounting for the per thread fault counters who triggered the
+	 * fault, and we skip the perf event updates.
 	 */
 	if (!regs)
 		return;
 
-	if (major) {
-		current->maj_flt++;
+	if (major)
 		perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs, address);
-	} else {
-		current->min_flt++;
+	else
 		perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs, address);
-	}
 }
 
 /*