The commit
07e8c82b5eff ("madvise: convert madvise_cold_or_pageout_pte_range() to
use folios") replaced the page_mapcount() with folio_mapcount() to
check whether the folio is shared by other mapping.

But it's not correct for large folio. folio_mapcount() returns the
total mapcount of large folio which is not suitable to detect whether
the folio is shared.

Use folio_estimated_sharers() which returns a estimated number of
shares. That means it's not 100% correct. But it should be OK for
madvise case here.

Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
---
 mm/madvise.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 38382a5d1e39..f12933ebcc24 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -383,7 +383,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
 		folio = pfn_folio(pmd_pfn(orig_pmd));
 
 		/* Do not interfere with other mappings of this folio */
-		if (folio_mapcount(folio) != 1)
+		if (folio_estimated_sharers(folio) != 1)
 			goto huge_unlock;
 
 		if (pageout_anon_only_filter && !folio_test_anon(folio))
@@ -459,7 +459,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
 		if (folio_test_large(folio)) {
 			int err;
 
-			if (folio_mapcount(folio) != 1)
+			if (folio_estimated_sharers(folio) != 1)
 				break;
 			if (pageout_anon_only_filter && !folio_test_anon(folio))
 				break;
@@ -682,7 +682,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
 		if (folio_test_large(folio)) {
 			int err;
 
-			if (folio_mapcount(folio) != 1)
+			if (folio_estimated_sharers(folio) != 1)
 				break;
 			if (!folio_trylock(folio))
 				break;
-- 
2.39.2

On Fri, Jul 21, 2023 at 3:41 AM Yin Fengwei <fengwei.yin@intel.com> wrote:
>
> The commit
> 07e8c82b5eff ("madvise: convert madvise_cold_or_pageout_pte_range() to
> use folios") replaced the page_mapcount() with folio_mapcount() to
> check whether the folio is shared by other mapping.
>
> But it's not correct for large folio. folio_mapcount() returns the
> total mapcount of large folio which is not suitable to detect whether
> the folio is shared.
>
> Use folio_estimated_sharers() which returns a estimated number of
> shares. That means it's not 100% correct. But it should be OK for
> madvise case here.
>
> Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>

Fixes:
Cc: stable

> @@ -383,7 +383,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
>                 folio = pfn_folio(pmd_pfn(orig_pmd));
>
>                 /* Do not interfere with other mappings of this folio */
> -               if (folio_mapcount(folio) != 1)
> +               if (folio_estimated_sharers(folio) != 1)

Strictly speaking, this isn't a bug. But it may be ok to include it in
the same patch.

>                         goto huge_unlock;
>
>                 if (pageout_anon_only_filter && !folio_test_anon(folio))
> @@ -459,7 +459,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
>                 if (folio_test_large(folio)) {
>                         int err;
>
> -                       if (folio_mapcount(folio) != 1)
> +                       if (folio_estimated_sharers(folio) != 1)
>                                 break;
>                         if (pageout_anon_only_filter && !folio_test_anon(folio))
>                                 break;
> @@ -682,7 +682,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,

What about madvise_free_huge_pmd()? Should it be changed as well so
that it's consistent with the first change? Either change both or neither.

>                 if (folio_test_large(folio)) {
>                         int err;
>
> -                       if (folio_mapcount(folio) != 1)
> +                       if (folio_estimated_sharers(folio) != 1)

This is another bug fix and should be in a separate patch.

>                                 break;
>                         if (!folio_trylock(folio))
>                                 break;

Please send two separate fixes, and then:

Reviewed-by: Yu Zhao <yuzhao@google.com>

On 7/22/2023 2:57 AM, Yu Zhao wrote:
> On Fri, Jul 21, 2023 at 3:41 AM Yin Fengwei <fengwei.yin@intel.com> wrote:
>>
>> The commit
>> 07e8c82b5eff ("madvise: convert madvise_cold_or_pageout_pte_range() to
>> use folios") replaced the page_mapcount() with folio_mapcount() to
>> check whether the folio is shared by other mapping.
>>
>> But it's not correct for large folio. folio_mapcount() returns the
>> total mapcount of large folio which is not suitable to detect whether
>> the folio is shared.
>>
>> Use folio_estimated_sharers() which returns a estimated number of
>> shares. That means it's not 100% correct. But it should be OK for
>> madvise case here.
>>
>> Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
> 
> Fixes:
> Cc: stable
OK

> 
>> @@ -383,7 +383,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
>>                 folio = pfn_folio(pmd_pfn(orig_pmd));
>>
>>                 /* Do not interfere with other mappings of this folio */
>> -               if (folio_mapcount(folio) != 1)
>> +               if (folio_estimated_sharers(folio) != 1)
> 
> Strictly speaking, this isn't a bug. But it may be ok to include it in
> the same patch.
OK. I will drop the change for pmd.

> 
>>                         goto huge_unlock;
>>
>>                 if (pageout_anon_only_filter && !folio_test_anon(folio))
>> @@ -459,7 +459,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
>>                 if (folio_test_large(folio)) {
>>                         int err;
>>
>> -                       if (folio_mapcount(folio) != 1)
>> +                       if (folio_estimated_sharers(folio) != 1)
>>                                 break;
>>                         if (pageout_anon_only_filter && !folio_test_anon(folio))
>>                                 break;
>> @@ -682,7 +682,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
> 
> What about madvise_free_huge_pmd()? Should it be changed as well so
> that it's consistent with the first change? Either change both or neither.
> 
>>                 if (folio_test_large(folio)) {
>>                         int err;
>>
>> -                       if (folio_mapcount(folio) != 1)
>> +                       if (folio_estimated_sharers(folio) != 1)
> 
> This is another bug fix and should be in a separate patch.
OK. Will split to two patches.

> 
>>                                 break;
>>                         if (!folio_trylock(folio))
>>                                 break;
> 
> Please send two separate fixes, and then:
> 
> Reviewed-by: Yu Zhao <yuzhao@google.com>
Thanks a lot. I will drop the mapcount() change for pmd and sent to patches
for madvise_cold_or_pageout_pte_range() and madvise_free_pte_range().


Regards
Yin, Fengwei

On Sun, Jul 23, 2023 at 6:27 AM Yin, Fengwei <fengwei.yin@intel.com> wrote:
>
>
>
> On 7/22/2023 2:57 AM, Yu Zhao wrote:
> > On Fri, Jul 21, 2023 at 3:41 AM Yin Fengwei <fengwei.yin@intel.com> wrote:
> >>
> >> The commit
> >> 07e8c82b5eff ("madvise: convert madvise_cold_or_pageout_pte_range() to
> >> use folios") replaced the page_mapcount() with folio_mapcount() to
> >> check whether the folio is shared by other mapping.
> >>
> >> But it's not correct for large folio. folio_mapcount() returns the
> >> total mapcount of large folio which is not suitable to detect whether
> >> the folio is shared.
> >>
> >> Use folio_estimated_sharers() which returns a estimated number of
> >> shares. That means it's not 100% correct. But it should be OK for
> >> madvise case here.
> >>
> >> Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
> >
> > Fixes:
> > Cc: stable
> OK
>
> >
> >> @@ -383,7 +383,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> >>                 folio = pfn_folio(pmd_pfn(orig_pmd));
> >>
> >>                 /* Do not interfere with other mappings of this folio */
> >> -               if (folio_mapcount(folio) != 1)
> >> +               if (folio_estimated_sharers(folio) != 1)
> >
> > Strictly speaking, this isn't a bug. But it may be ok to include it in
> > the same patch.
> OK. I will drop the change for pmd.
>
> >
> >>                         goto huge_unlock;
> >>
> >>                 if (pageout_anon_only_filter && !folio_test_anon(folio))
> >> @@ -459,7 +459,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> >>                 if (folio_test_large(folio)) {
> >>                         int err;
> >>
> >> -                       if (folio_mapcount(folio) != 1)
> >> +                       if (folio_estimated_sharers(folio) != 1)
> >>                                 break;
> >>                         if (pageout_anon_only_filter && !folio_test_anon(folio))
> >>                                 break;
> >> @@ -682,7 +682,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
> >
> > What about madvise_free_huge_pmd()? Should it be changed as well so
> > that it's consistent with the first change? Either change both or neither.
> >
> >>                 if (folio_test_large(folio)) {
> >>                         int err;
> >>
> >> -                       if (folio_mapcount(folio) != 1)
> >> +                       if (folio_estimated_sharers(folio) != 1)
> >
> > This is another bug fix and should be in a separate patch.
> OK. Will split to two patches.
>
> >
> >>                                 break;
> >>                         if (!folio_trylock(folio))
> >>                                 break;
> >
> > Please send two separate fixes, and then:
> >
> > Reviewed-by: Yu Zhao <yuzhao@google.com>
> Thanks a lot. I will drop the mapcount() change for pmd and sent to patches
> for madvise_cold_or_pageout_pte_range() and madvise_free_pte_range().

I don't mind including the PMD changes. Either way works for me :)