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damon: Use pmdp_get instead of drect dereferencing pmd.

PATCH Superseded Levi Yun 3 participants 5 messages Jul 27, 2023 – Jul 28, 2023

Subsystems (2)
Memory management DAMON

v1 of 2 Superseded Latest is v2 →

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Levi Yun

author
#0 lore raw

PATCH 1/1 damon: Use pmdp_get instead of drect dereferencing pmd.

As ptep_get, Use the pmdp_get wrapper when we accessing pmdval instead of direct dereferencing pmd.

Signed-off-by Levi Yun <[email protected]>
---
 mm/damon/ops-common.c |  2 +-
 mm/damon/paddr.c      |  2 +-
 mm/damon/vaddr.c      | 22 ++++++++++++++--------
 3 files changed, 16 insertions(+), 10 deletions(-)
mm/damon/ops-common.c +1 -1
index e940802a15a4..ac1c3fa80f98 100644
@@ -54,7 +54,7 @@ void damon_ptep_mkold(pte_t *pte, struct vm_area_struct *vma, unsigned long addr
 void damon_pmdp_mkold(pmd_t *pmd, struct vm_area_struct *vma, unsigned long addr)
 {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	struct folio *folio = damon_get_folio(pmd_pfn(*pmd));
+	struct folio *folio = damon_get_folio(pmd_pfn(pmdp_get(pmd)));
 
 	if (!folio)
 		return;
mm/damon/paddr.c +1 -1
index 40801e38fcf0..909db25efb35 100644
@@ -94,7 +94,7 @@ static bool __damon_pa_young(struct folio *folio, struct vm_area_struct *vma,
 				mmu_notifier_test_young(vma->vm_mm, addr);
 		} else {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-			*accessed = pmd_young(*pvmw.pmd) ||
+			*accessed = pmd_young(pmdp_get(pvmw.pmd)) ||
 				!folio_test_idle(folio) ||
 				mmu_notifier_test_young(vma->vm_mm, addr);
 #else
mm/damon/vaddr.c +14 -8
index 2fcc9731528a..82f7865719fe 100644
@@ -301,16 +301,19 @@ static int damon_mkold_pmd_entry(pmd_t *pmd, unsigned long addr,
 		unsigned long next, struct mm_walk *walk)
 {
 	pte_t *pte;
+	pmd_t pmde;
 	spinlock_t *ptl;
 
-	if (pmd_trans_huge(*pmd)) {
+	if (pmd_trans_huge(pmdp_get_lockless(pmd))) {
 		ptl = pmd_lock(walk->mm, pmd);
-		if (!pmd_present(*pmd)) {
+		pmde = pmdp_get(pmd);
+
+		if (!pmd_present(pmde)) {
 			spin_unlock(ptl);
 			return 0;
 		}
 
-		if (pmd_trans_huge(*pmd)) {
+		if (pmd_trans_huge(pmde)) {
 			damon_pmdp_mkold(pmd, walk->vma, addr);
 			spin_unlock(ptl);
 			return 0;

@@ -434,26 +437,29 @@ static int damon_young_pmd_entry(pmd_t *pmd, unsigned long addr,
 {
 	pte_t *pte;
 	pte_t ptent;
+	pmd_t pmde;
 	spinlock_t *ptl;
 	struct folio *folio;
 	struct damon_young_walk_private *priv = walk->private;
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	if (pmd_trans_huge(*pmd)) {
+	if (pmd_trans_huge(pmdp_get_lockless(pmd))) {
 		ptl = pmd_lock(walk->mm, pmd);
-		if (!pmd_present(*pmd)) {
+		pmde = pmdp_get(pmd);
+
+		if (!pmd_present(pmde)) {
 			spin_unlock(ptl);
 			return 0;
 		}
 
-		if (!pmd_trans_huge(*pmd)) {
+		if (!pmd_trans_huge(pmde)) {
 			spin_unlock(ptl);
 			goto regular_page;
 		}
-		folio = damon_get_folio(pmd_pfn(*pmd));
+		folio = damon_get_folio(pmd_pfn(pmde));
 		if (!folio)
 			goto huge_out;
-		if (pmd_young(*pmd) || !folio_test_idle(folio) ||
+		if (pmd_young(pmde) || !folio_test_idle(folio) ||
 					mmu_notifier_test_young(walk->mm,
 						addr))
 			priv->young = true;
Signature · 1 line
2.37.2
maintainer
#1 lore raw

Hi Levi,

Thank you for this patch.

Nit for the subject, what about s/drect/directly/? Also, let's remove the period at the end.

Quoted 2 lines · On Fri, 28 Jul 2023 03:37:45 +0900 Levi Yun <[email protected]> wrote:

As ptep_get, Use the pmdp_get wrapper when we accessing pmdval instead of direct dereferencing pmd.

Nit: s/Use/use/ and s/direct/directly

Quoted 39 lines
Signed-off-by Levi Yun <[email protected]>
---
 mm/damon/ops-common.c |  2 +-
 mm/damon/paddr.c      |  2 +-
 mm/damon/vaddr.c      | 22 ++++++++++++++--------
 3 files changed, 16 insertions(+), 10 deletions(-)
mm/damon/ops-common.c +1 -1
index e940802a15a4..ac1c3fa80f98 100644
@@ -54,7 +54,7 @@ void damon_ptep_mkold(pte_t *pte, struct vm_area_struct *vma, unsigned long addr
 void damon_pmdp_mkold(pmd_t *pmd, struct vm_area_struct *vma, unsigned long addr)
 {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	struct folio *folio = damon_get_folio(pmd_pfn(*pmd));
+	struct folio *folio = damon_get_folio(pmd_pfn(pmdp_get(pmd)));
 
 	if (!folio)
 		return;
mm/damon/paddr.c +1 -1
index 40801e38fcf0..909db25efb35 100644
@@ -94,7 +94,7 @@ static bool __damon_pa_young(struct folio *folio, struct vm_area_struct *vma,
 				mmu_notifier_test_young(vma->vm_mm, addr);
 		} else {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-			*accessed = pmd_young(*pvmw.pmd) ||
+			*accessed = pmd_young(pmdp_get(pvmw.pmd)) ||
 				!folio_test_idle(folio) ||
 				mmu_notifier_test_young(vma->vm_mm, addr);
 #else
mm/damon/vaddr.c +0 -0
index 2fcc9731528a..82f7865719fe 100644

mm/damon/vaddr.c static int damon_mkold_pmd_entry(pmd_t *pmd, unsigned long addr, · line 307

Quoted 8 lines
mm/damon/vaddr.c +2 -1
@@ -301,16 +301,19 @@ static int damon_mkold_pmd_entry(pmd_t *pmd, unsigned long addr,
 		unsigned long next, struct mm_walk *walk)
 {
 	pte_t *pte;
+	pmd_t pmde;
 	spinlock_t *ptl;
 
-	if (pmd_trans_huge(*pmd)) {
+	if (pmd_trans_huge(pmdp_get_lockless(pmd))) {

I don't think we really need to use pmdp_get_lockless() here, since we will do this check again with the lock, and we have the fallback for the intermediate changes.

Quoted 15 lines
mm/damon/vaddr.c +4 -2
 		ptl = pmd_lock(walk->mm, pmd);
-		if (!pmd_present(*pmd)) {
+		pmde = pmdp_get(pmd);
+
+		if (!pmd_present(pmde)) {
 			spin_unlock(ptl);
 			return 0;
 		}
 
-		if (pmd_trans_huge(*pmd)) {
+		if (pmd_trans_huge(pmde)) {
 			damon_pmdp_mkold(pmd, walk->vma, addr);
 			spin_unlock(ptl);
 			return 0;

mm/damon/vaddr.c static int damon_young_pmd_entry(pmd_t *pmd, unsigned long addr, · line 440

Quoted 4 lines
mm/damon/vaddr.c +1 -0
@@ -434,26 +437,29 @@ static int damon_young_pmd_entry(pmd_t *pmd, unsigned long addr,
 {
 	pte_t *pte;
 	pte_t ptent;
+	pmd_t pmde;

This would cause below build warning if CONFIG_TRANSPARENT_HUGEPAGE is not defined.

.../mm/damon/vaddr.c:440:8: warning: unused variable 'pmde' [-Wunused-variable]

  440 |  pmd_t pmde;
      |        ^~~~

mm/damon/vaddr.c static int damon_young_pmd_entry(pmd_t *pmd, unsigned long addr, · line 446

Quoted 7 lines
mm/damon/vaddr.c +1 -1
 	spinlock_t *ptl;
 	struct folio *folio;
 	struct damon_young_walk_private *priv = walk->private;
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	if (pmd_trans_huge(*pmd)) {
+	if (pmd_trans_huge(pmdp_get_lockless(pmd))) {

Again, pmdp_get() might be enough?

Quoted 26 lines
mm/damon/vaddr.c +6 -4
 		ptl = pmd_lock(walk->mm, pmd);
-		if (!pmd_present(*pmd)) {
+		pmde = pmdp_get(pmd);
+
+		if (!pmd_present(pmde)) {
 			spin_unlock(ptl);
 			return 0;
 		}
 
-		if (!pmd_trans_huge(*pmd)) {
+		if (!pmd_trans_huge(pmde)) {
 			spin_unlock(ptl);
 			goto regular_page;
 		}
-		folio = damon_get_folio(pmd_pfn(*pmd));
+		folio = damon_get_folio(pmd_pfn(pmde));
 		if (!folio)
 			goto huge_out;
-		if (pmd_young(*pmd) || !folio_test_idle(folio) ||
+		if (pmd_young(pmde) || !folio_test_idle(folio) ||
 					mmu_notifier_test_young(walk->mm,
 						addr))
 			priv->young = true;
Signature · 1 line
2.37.2

Thanks,
SJ

author
#2 lore raw

Hi SJ.

Thanks for looking into this.

Quoted 4 lines

Nit for the subject, what about s/drect/directly/? Also, let's remove the period at the end.

On Fri, 28 Jul 2023 03:37:45 +0900 Levi Yun <[email protected]> wrote:

Thanks. But I don't know why period is added thou I sent via git send-email ..

Quoted 6 lines

Review

Quoted 2 lines
(quoted diff) +1 -1
-     if (pmd_trans_huge(*pmd)) {
+     if (pmd_trans_huge(pmdp_get_lockless(pmd))) {

I don't think we really need to use pmdp_get_lockless() here, since we will do this check again with the lock, and we have the fallback for the intermediate changes.

Agree. I'll change. Thanks :)

Quoted 9 lines

mm/damon/vaddr.c static int damon_young_pmd_entry(pmd_t *pmd, unsigned long addr, · line 440

Quoted 5 lines
mm/damon/vaddr.c +1 -0
@@ -434,26 +437,29 @@ static int damon_young_pmd_entry(pmd_t *pmd, unsigned long addr,
 {
      pte_t *pte;
      pte_t ptent;
+     pmd_t pmde;

This would cause below build warning if CONFIG_TRANSPARENT_HUGEPAGE is not defined.

Quoted 12 lines

.../mm/damon/vaddr.c:440:8: warning: unused variable 'pmde' [-Wunused-variable]

  440 |  pmd_t pmde;
      |        ^~~~
Quoted 7 lines
mm/damon/vaddr.c +1 -1
      spinlock_t *ptl;
      struct folio *folio;
      struct damon_young_walk_private *priv = walk->private;
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-     if (pmd_trans_huge(*pmd)) {
+     if (pmd_trans_huge(pmdp_get_lockless(pmd))) {

Oh.. I miss this. Many thanks..!

Quoted 2 lines

Thanks,
SJ

Many Thanks..!

---------
Sincerely,
Levi.

build bot
#3 lore raw
In reply to Levi Yun
kernel test robot noticed the following build warnings:

Hi Levi,

kernel test robot noticed the following build warnings:

[auto build test WARNING on akpm-mm/mm-everything]
[also build test WARNING on linus/master v6.5-rc3 next-20230728] [cannot apply to sj/damon/next]
[If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Levi-Yun/damon-Use-pmdp_get-instead-of-drect-dereferencing-pmd/20230728-024044
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20230727183745.682880-1-ppbuk5246%40gmail.com
patch subject: [PATCH] damon: Use pmdp_get instead of drect dereferencing pmd.
config: i386-randconfig-i016-20230727 (https://download.01.org/0day-ci/archive/20230728/[email protected]/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce: (https://download.01.org/0day-ci/archive/20230728/[email protected]/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <[email protected]>
| Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/

All warnings (new ones prefixed by >>):

mm/damon/vaddr.c: In function 'damon_young_pmd_entry':

>> mm/damon/vaddr.c:440:15: warning: unused variable 'pmde' [-Wunused-variable]
     440 |         pmd_t pmde;
         |               ^~~~

vim +/pmde +440 mm/damon/vaddr.c

434
435 static int damon_young_pmd_entry(pmd_t *pmd, unsigned long addr,
436 unsigned long next, struct mm_walk *walk)
437 {
438 pte_t *pte;
439 pte_t ptent;

 > 440		pmd_t pmde;

441 spinlock_t *ptl;
442 struct folio *folio;
443 struct damon_young_walk_private *priv = walk->private;
444

Signature · 2 lines
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
author
#4 lore raw

This build warning is fixed in v2:

    https://lore.kernel.org/all/[email protected]/
Quoted 51 lines · kernel test robot

Hi Levi,

kernel test robot noticed the following build warnings:

[auto build test WARNING on akpm-mm/mm-everything]
[also build test WARNING on linus/master v6.5-rc3 next-20230728] [cannot apply to sj/damon/next]
[If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Levi-Yun/damon-Use-pmdp_get-instead-of-drect-dereferencing-pmd/20230728-024044
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20230727183745.682880-1-ppbuk5246%40gmail.com
patch subject: [PATCH] damon: Use pmdp_get instead of drect dereferencing pmd.
config: i386-randconfig-i016-20230727 (https://download.01.org/0day-ci/archive/20230728/[email protected]/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce: (https://download.01.org/0day-ci/archive/20230728/[email protected]/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <[email protected]>
| Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/

All warnings (new ones prefixed by >>):

mm/damon/vaddr.c: In function 'damon_young_pmd_entry':

Quoted 1 line
Quoted 1 line

mm/damon/vaddr.c:440:15: warning: unused variable 'pmde' [-Wunused-variable]

     440 |         pmd_t pmde;
         |               ^~~~

vim +/pmde +440 mm/damon/vaddr.c

   434
   435  static int damon_young_pmd_entry(pmd_t *pmd, unsigned long addr,
   436                  unsigned long next, struct mm_walk *walk)
   437  {
   438          pte_t *pte;
   439          pte_t ptent;
Quoted 1 line

440 pmd_t pmde;

   441          spinlock_t *ptl;
   442          struct folio *folio;
   443          struct damon_young_walk_private *priv = walk->private;

444

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki