diff mbox series

[v1,1/2] mm/migrate: make migrate_misplaced_folio() return 0 on success

Message ID 20240620212935.656243-2-david@redhat.com (mailing list archive)
State New
Headers show
Series mm/migrate: move NUMA hinting fault folio isolation + checks under PTL | expand

Commit Message

David Hildenbrand June 20, 2024, 9:29 p.m. UTC 
Let's just return 0 on success, which is less confusing.

... especially because we got it wrong in the migrate.h stub where we
have "return -EAGAIN; /* can't migrate now */" instead of "return 0;".
Likely this wrong return value doesn't currently matter, but it
certainly adds confusion.

We'll add migrate_misplaced_folio_prepare() next, where we want to use
the same "return 0 on success" approach, so let's just clean this up.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/huge_memory.c | 5 ++---
 mm/memory.c      | 2 +-
 mm/migrate.c     | 4 ++--
 3 files changed, 5 insertions(+), 6 deletions(-)

Comments

Zi Yan June 21, 2024, 1:40 a.m. UTC | #1 
On 20 Jun 2024, at 17:29, David Hildenbrand wrote:

> Let's just return 0 on success, which is less confusing.
>
> ... especially because we got it wrong in the migrate.h stub where we
> have "return -EAGAIN; /* can't migrate now */" instead of "return 0;".
> Likely this wrong return value doesn't currently matter, but it
> certainly adds confusion.
>
> We'll add migrate_misplaced_folio_prepare() next, where we want to use
> the same "return 0 on success" approach, so let's just clean this up.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  mm/huge_memory.c | 5 ++---
>  mm/memory.c      | 2 +-
>  mm/migrate.c     | 4 ++--
>  3 files changed, 5 insertions(+), 6 deletions(-)
>

LGTM. Reviewed-by: Zi Yan <ziy@nvidia.com>

--
Best Regards,
Yan, Zi
Baolin Wang June 21, 2024, 3:39 a.m. UTC | #2 
On 2024/6/21 05:29, David Hildenbrand wrote:
> Let's just return 0 on success, which is less confusing.
> 
> ... especially because we got it wrong in the migrate.h stub where we
> have "return -EAGAIN; /* can't migrate now */" instead of "return 0;".
> Likely this wrong return value doesn't currently matter, but it
> certainly adds confusion.
> 
> We'll add migrate_misplaced_folio_prepare() next, where we want to use
> the same "return 0 on success" approach, so let's just clean this up
LGTM.
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>

> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>   mm/huge_memory.c | 5 ++---
>   mm/memory.c      | 2 +-
>   mm/migrate.c     | 4 ++--
>   3 files changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 0fffaa58a47a..fc27dabcd8e3 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1652,7 +1652,7 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
>   	unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
>   	int nid = NUMA_NO_NODE;
>   	int target_nid, last_cpupid = (-1 & LAST_CPUPID_MASK);
> -	bool migrated = false, writable = false;
> +	bool writable = false;
>   	int flags = 0;
>   
>   	vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
> @@ -1696,8 +1696,7 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
>   	spin_unlock(vmf->ptl);
>   	writable = false;
>   
> -	migrated = migrate_misplaced_folio(folio, vma, target_nid);
> -	if (migrated) {
> +	if (!migrate_misplaced_folio(folio, vma, target_nid)) {
>   		flags |= TNF_MIGRATED;
>   		nid = target_nid;
>   	} else {
> diff --git a/mm/memory.c b/mm/memory.c
> index 00728ea95583..118660de5bcc 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -5354,7 +5354,7 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
>   	ignore_writable = true;
>   
>   	/* Migrate to the requested node */
> -	if (migrate_misplaced_folio(folio, vma, target_nid)) {
> +	if (!migrate_misplaced_folio(folio, vma, target_nid)) {
>   		nid = target_nid;
>   		flags |= TNF_MIGRATED;
>   	} else {
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 781979567f64..0307b54879a0 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2629,11 +2629,11 @@ int migrate_misplaced_folio(struct folio *folio, struct vm_area_struct *vma,
>   					    nr_succeeded);
>   	}
>   	BUG_ON(!list_empty(&migratepages));
> -	return isolated;
> +	return isolated ? 0 : -EAGAIN;
>   
>   out:
>   	folio_put(folio);
> -	return 0;
> +	return -EAGAIN;
>   }
>   #endif /* CONFIG_NUMA_BALANCING */
>   #endif /* CONFIG_NUMA */
Huang, Ying July 1, 2024, 7:36 a.m. UTC | #3 
David Hildenbrand <david@redhat.com> writes:

> Let's just return 0 on success, which is less confusing.
>
> ... especially because we got it wrong in the migrate.h stub where we
> have "return -EAGAIN; /* can't migrate now */" instead of "return 0;".
> Likely this wrong return value doesn't currently matter, but it
> certainly adds confusion.
>
> We'll add migrate_misplaced_folio_prepare() next, where we want to use
> the same "return 0 on success" approach, so let's just clean this up.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  mm/huge_memory.c | 5 ++---
>  mm/memory.c      | 2 +-
>  mm/migrate.c     | 4 ++--
>  3 files changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 0fffaa58a47a..fc27dabcd8e3 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1652,7 +1652,7 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
>  	unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
>  	int nid = NUMA_NO_NODE;
>  	int target_nid, last_cpupid = (-1 & LAST_CPUPID_MASK);
> -	bool migrated = false, writable = false;
> +	bool writable = false;
>  	int flags = 0;
>  
>  	vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
> @@ -1696,8 +1696,7 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
>  	spin_unlock(vmf->ptl);
>  	writable = false;
>  
> -	migrated = migrate_misplaced_folio(folio, vma, target_nid);
> -	if (migrated) {
> +	if (!migrate_misplaced_folio(folio, vma, target_nid)) {
>  		flags |= TNF_MIGRATED;
>  		nid = target_nid;
>  	} else {
> diff --git a/mm/memory.c b/mm/memory.c
> index 00728ea95583..118660de5bcc 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -5354,7 +5354,7 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
>  	ignore_writable = true;
>  
>  	/* Migrate to the requested node */
> -	if (migrate_misplaced_folio(folio, vma, target_nid)) {
> +	if (!migrate_misplaced_folio(folio, vma, target_nid)) {
>  		nid = target_nid;
>  		flags |= TNF_MIGRATED;
>  	} else {
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 781979567f64..0307b54879a0 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2629,11 +2629,11 @@ int migrate_misplaced_folio(struct folio *folio, struct vm_area_struct *vma,
>  					    nr_succeeded);
>  	}
>  	BUG_ON(!list_empty(&migratepages));
> -	return isolated;
> +	return isolated ? 0 : -EAGAIN;

Is it good to use -EAGAIN as error code always?  At least if
nr_remaining < 0, we can use that?

Otherwise, this LGTM.  Thanks!

>  
>  out:
>  	folio_put(folio);
> -	return 0;
> +	return -EAGAIN;
>  }
>  #endif /* CONFIG_NUMA_BALANCING */
>  #endif /* CONFIG_NUMA */

--
Best Regards,
Huang, Ying
David Hildenbrand July 1, 2024, 7:44 a.m. UTC | #4 
On 01.07.24 09:36, Huang, Ying wrote:
> David Hildenbrand <david@redhat.com> writes:
> 
>> Let's just return 0 on success, which is less confusing.
>>
>> ... especially because we got it wrong in the migrate.h stub where we
>> have "return -EAGAIN; /* can't migrate now */" instead of "return 0;".
>> Likely this wrong return value doesn't currently matter, but it
>> certainly adds confusion.
>>
>> We'll add migrate_misplaced_folio_prepare() next, where we want to use
>> the same "return 0 on success" approach, so let's just clean this up.
>>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>>   mm/huge_memory.c | 5 ++---
>>   mm/memory.c      | 2 +-
>>   mm/migrate.c     | 4 ++--
>>   3 files changed, 5 insertions(+), 6 deletions(-)
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 0fffaa58a47a..fc27dabcd8e3 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -1652,7 +1652,7 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
>>   	unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
>>   	int nid = NUMA_NO_NODE;
>>   	int target_nid, last_cpupid = (-1 & LAST_CPUPID_MASK);
>> -	bool migrated = false, writable = false;
>> +	bool writable = false;
>>   	int flags = 0;
>>   
>>   	vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
>> @@ -1696,8 +1696,7 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
>>   	spin_unlock(vmf->ptl);
>>   	writable = false;
>>   
>> -	migrated = migrate_misplaced_folio(folio, vma, target_nid);
>> -	if (migrated) {
>> +	if (!migrate_misplaced_folio(folio, vma, target_nid)) {
>>   		flags |= TNF_MIGRATED;
>>   		nid = target_nid;
>>   	} else {
>> diff --git a/mm/memory.c b/mm/memory.c
>> index 00728ea95583..118660de5bcc 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -5354,7 +5354,7 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
>>   	ignore_writable = true;
>>   
>>   	/* Migrate to the requested node */
>> -	if (migrate_misplaced_folio(folio, vma, target_nid)) {
>> +	if (!migrate_misplaced_folio(folio, vma, target_nid)) {
>>   		nid = target_nid;
>>   		flags |= TNF_MIGRATED;
>>   	} else {
>> diff --git a/mm/migrate.c b/mm/migrate.c
>> index 781979567f64..0307b54879a0 100644
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -2629,11 +2629,11 @@ int migrate_misplaced_folio(struct folio *folio, struct vm_area_struct *vma,
>>   					    nr_succeeded);
>>   	}
>>   	BUG_ON(!list_empty(&migratepages));
>> -	return isolated;
>> +	return isolated ? 0 : -EAGAIN;
> 
> Is it good to use -EAGAIN as error code always?  At least if
> nr_remaining < 0, we can use that?

Thanks for the review. I kept it simple for now, because the 
migrate_misplaced_folio_prepare() stub has:

	return -EAGAIN; /* can't migrate now */

and it doesn't really make a difference right now which exact return 
value we use.

(maybe some cases, like the stub, should return -EINVAL or -EOPNOTSUPP 
once we start caring about the exact value)
diff mbox series

Patch

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 0fffaa58a47a..fc27dabcd8e3 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1652,7 +1652,7 @@  vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
 	unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
 	int nid = NUMA_NO_NODE;
 	int target_nid, last_cpupid = (-1 & LAST_CPUPID_MASK);
-	bool migrated = false, writable = false;
+	bool writable = false;
 	int flags = 0;
 
 	vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
@@ -1696,8 +1696,7 @@  vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
 	spin_unlock(vmf->ptl);
 	writable = false;
 
-	migrated = migrate_misplaced_folio(folio, vma, target_nid);
-	if (migrated) {
+	if (!migrate_misplaced_folio(folio, vma, target_nid)) {
 		flags |= TNF_MIGRATED;
 		nid = target_nid;
 	} else {
diff --git a/mm/memory.c b/mm/memory.c
index 00728ea95583..118660de5bcc 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5354,7 +5354,7 @@  static vm_fault_t do_numa_page(struct vm_fault *vmf)
 	ignore_writable = true;
 
 	/* Migrate to the requested node */
-	if (migrate_misplaced_folio(folio, vma, target_nid)) {
+	if (!migrate_misplaced_folio(folio, vma, target_nid)) {
 		nid = target_nid;
 		flags |= TNF_MIGRATED;
 	} else {
diff --git a/mm/migrate.c b/mm/migrate.c
index 781979567f64..0307b54879a0 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2629,11 +2629,11 @@  int migrate_misplaced_folio(struct folio *folio, struct vm_area_struct *vma,
 					    nr_succeeded);
 	}
 	BUG_ON(!list_empty(&migratepages));
-	return isolated;
+	return isolated ? 0 : -EAGAIN;
 
 out:
 	folio_put(folio);
-	return 0;
+	return -EAGAIN;
 }
 #endif /* CONFIG_NUMA_BALANCING */
 #endif /* CONFIG_NUMA */