From: Khalid Aziz <khalid@kernel.org>
Add a bit to vm_flags to indicate a vma shares PTEs with others. Add
a function to determine if a vma shares PTEs by checking this flag.
This is to be used to find the shared page table entries on page fault
for vmas sharing PTEs.
Signed-off-by: Khalid Aziz <khalid@kernel.org>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
---
include/linux/mm.h | 7 +++++++
include/trace/events/mmflags.h | 3 +++
mm/internal.h | 5 +++++
3 files changed, 15 insertions(+)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6549d0979b28..3aa0b3322284 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -413,6 +413,13 @@ extern unsigned int kobjsize(const void *objp);
#define VM_DROPPABLE VM_NONE
#endif
+#ifdef CONFIG_64BIT
+#define VM_SHARED_PT_BIT 41
+#define VM_SHARED_PT BIT(VM_SHARED_PT_BIT)
+#else
+#define VM_SHARED_PT VM_NONE
+#endif
+
#ifdef CONFIG_64BIT
/* VM is sealed, in vm_flags */
#define VM_SEALED _BITUL(63)
diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
index b63d211bd141..e1ae1e60d086 100644
--- a/include/trace/events/mmflags.h
+++ b/include/trace/events/mmflags.h
@@ -167,8 +167,10 @@ IF_HAVE_PG_ARCH_X(arch_3)
#ifdef CONFIG_64BIT
# define IF_HAVE_VM_DROPPABLE(flag, name) {flag, name},
+# define IF_HAVE_VM_SHARED_PT(flag, name) {flag, name},
#else
# define IF_HAVE_VM_DROPPABLE(flag, name)
+# define IF_HAVE_VM_SHARED_PT(flag, name)
#endif
#define __def_vmaflag_names \
@@ -204,6 +206,7 @@ IF_HAVE_VM_SOFTDIRTY(VM_SOFTDIRTY, "softdirty" ) \
{VM_HUGEPAGE, "hugepage" }, \
{VM_NOHUGEPAGE, "nohugepage" }, \
IF_HAVE_VM_DROPPABLE(VM_DROPPABLE, "droppable" ) \
+IF_HAVE_VM_SHARED_PT(VM_SHARED_PT, "sharedpt" ) \
{VM_MERGEABLE, "mergeable" } \
#define show_vma_flags(flags) \
diff --git a/mm/internal.h b/mm/internal.h
index b4d86436565b..8005d5956b6e 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1578,4 +1578,9 @@ void unlink_file_vma_batch_init(struct unlink_vma_file_batch *);
void unlink_file_vma_batch_add(struct unlink_vma_file_batch *, struct vm_area_struct *);
void unlink_file_vma_batch_final(struct unlink_vma_file_batch *);
+static inline bool vma_is_shared(const struct vm_area_struct *vma)
+{
+ return VM_SHARED_PT && (vma->vm_flags & VM_SHARED_PT);
+}
+
#endif /* __MM_INTERNAL_H */
--
2.43.5On Tue, Sep 3, 2024 at 4:23 PM Anthony Yznaga <anthony.yznaga@oracle.com> wrote:
>
> From: Khalid Aziz <khalid@kernel.org>
>
> Add a bit to vm_flags to indicate a vma shares PTEs with others. Add
> a function to determine if a vma shares PTEs by checking this flag.
> This is to be used to find the shared page table entries on page fault
> for vmas sharing PTEs.
>
> Signed-off-by: Khalid Aziz <khalid@kernel.org>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
> ---
> include/linux/mm.h | 7 +++++++
> include/trace/events/mmflags.h | 3 +++
> mm/internal.h | 5 +++++
> 3 files changed, 15 insertions(+)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 6549d0979b28..3aa0b3322284 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -413,6 +413,13 @@ extern unsigned int kobjsize(const void *objp);
> #define VM_DROPPABLE VM_NONE
> #endif
>
> +#ifdef CONFIG_64BIT
> +#define VM_SHARED_PT_BIT 41
> +#define VM_SHARED_PT BIT(VM_SHARED_PT_BIT)
> +#else
> +#define VM_SHARED_PT VM_NONE
> +#endif
> +
> #ifdef CONFIG_64BIT
> /* VM is sealed, in vm_flags */
> #define VM_SEALED _BITUL(63)
> diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
> index b63d211bd141..e1ae1e60d086 100644
> --- a/include/trace/events/mmflags.h
> +++ b/include/trace/events/mmflags.h
> @@ -167,8 +167,10 @@ IF_HAVE_PG_ARCH_X(arch_3)
>
> #ifdef CONFIG_64BIT
> # define IF_HAVE_VM_DROPPABLE(flag, name) {flag, name},
> +# define IF_HAVE_VM_SHARED_PT(flag, name) {flag, name},
> #else
> # define IF_HAVE_VM_DROPPABLE(flag, name)
> +# define IF_HAVE_VM_SHARED_PT(flag, name)
> #endif
>
> #define __def_vmaflag_names \
> @@ -204,6 +206,7 @@ IF_HAVE_VM_SOFTDIRTY(VM_SOFTDIRTY, "softdirty" ) \
> {VM_HUGEPAGE, "hugepage" }, \
> {VM_NOHUGEPAGE, "nohugepage" }, \
> IF_HAVE_VM_DROPPABLE(VM_DROPPABLE, "droppable" ) \
> +IF_HAVE_VM_SHARED_PT(VM_SHARED_PT, "sharedpt" ) \
> {VM_MERGEABLE, "mergeable" } \
>
> #define show_vma_flags(flags) \
> diff --git a/mm/internal.h b/mm/internal.h
> index b4d86436565b..8005d5956b6e 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -1578,4 +1578,9 @@ void unlink_file_vma_batch_init(struct unlink_vma_file_batch *);
> void unlink_file_vma_batch_add(struct unlink_vma_file_batch *, struct vm_area_struct *);
> void unlink_file_vma_batch_final(struct unlink_vma_file_batch *);
>
Hi Anthony,
I'm really excited to see this series on the mailing list again! :) I
won't have time to review this series in too much detail, but I hope
something like it gets merged eventually.
> +static inline bool vma_is_shared(const struct vm_area_struct *vma)
> +{
> + return VM_SHARED_PT && (vma->vm_flags & VM_SHARED_PT);
> +}
Tiny comment - I find vma_is_shared() to be a bit of a confusing name,
especially given how vma_is_shared_maywrite() is defined. (Sorry if
this has already been discussed before.)
How about vma_is_shared_pt()?
On 04.09.24 01:40, James Houghton wrote:
> On Tue, Sep 3, 2024 at 4:23 PM Anthony Yznaga <anthony.yznaga@oracle.com> wrote:
>>
>> From: Khalid Aziz <khalid@kernel.org>
>>
>> Add a bit to vm_flags to indicate a vma shares PTEs with others. Add
>> a function to determine if a vma shares PTEs by checking this flag.
>> This is to be used to find the shared page table entries on page fault
>> for vmas sharing PTEs.
>>
>> Signed-off-by: Khalid Aziz <khalid@kernel.org>
>> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
>> Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
>> ---
>> include/linux/mm.h | 7 +++++++
>> include/trace/events/mmflags.h | 3 +++
>> mm/internal.h | 5 +++++
>> 3 files changed, 15 insertions(+)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 6549d0979b28..3aa0b3322284 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -413,6 +413,13 @@ extern unsigned int kobjsize(const void *objp);
>> #define VM_DROPPABLE VM_NONE
>> #endif
>>
>> +#ifdef CONFIG_64BIT
>> +#define VM_SHARED_PT_BIT 41
>> +#define VM_SHARED_PT BIT(VM_SHARED_PT_BIT)
>> +#else
>> +#define VM_SHARED_PT VM_NONE
>> +#endif
>> +
>> #ifdef CONFIG_64BIT
>> /* VM is sealed, in vm_flags */
>> #define VM_SEALED _BITUL(63)
>> diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
>> index b63d211bd141..e1ae1e60d086 100644
>> --- a/include/trace/events/mmflags.h
>> +++ b/include/trace/events/mmflags.h
>> @@ -167,8 +167,10 @@ IF_HAVE_PG_ARCH_X(arch_3)
>>
>> #ifdef CONFIG_64BIT
>> # define IF_HAVE_VM_DROPPABLE(flag, name) {flag, name},
>> +# define IF_HAVE_VM_SHARED_PT(flag, name) {flag, name},
>> #else
>> # define IF_HAVE_VM_DROPPABLE(flag, name)
>> +# define IF_HAVE_VM_SHARED_PT(flag, name)
>> #endif
>>
>> #define __def_vmaflag_names \
>> @@ -204,6 +206,7 @@ IF_HAVE_VM_SOFTDIRTY(VM_SOFTDIRTY, "softdirty" ) \
>> {VM_HUGEPAGE, "hugepage" }, \
>> {VM_NOHUGEPAGE, "nohugepage" }, \
>> IF_HAVE_VM_DROPPABLE(VM_DROPPABLE, "droppable" ) \
>> +IF_HAVE_VM_SHARED_PT(VM_SHARED_PT, "sharedpt" ) \
>> {VM_MERGEABLE, "mergeable" } \
>>
>> #define show_vma_flags(flags) \
>> diff --git a/mm/internal.h b/mm/internal.h
>> index b4d86436565b..8005d5956b6e 100644
>> --- a/mm/internal.h
>> +++ b/mm/internal.h
>> @@ -1578,4 +1578,9 @@ void unlink_file_vma_batch_init(struct unlink_vma_file_batch *);
>> void unlink_file_vma_batch_add(struct unlink_vma_file_batch *, struct vm_area_struct *);
>> void unlink_file_vma_batch_final(struct unlink_vma_file_batch *);
>>
>
> Hi Anthony,
>
> I'm really excited to see this series on the mailing list again! :) I
> won't have time to review this series in too much detail, but I hope
> something like it gets merged eventually.
>
>> +static inline bool vma_is_shared(const struct vm_area_struct *vma)
>> +{
>> + return VM_SHARED_PT && (vma->vm_flags & VM_SHARED_PT);
>> +}
>
> Tiny comment - I find vma_is_shared() to be a bit of a confusing name,
> especially given how vma_is_shared_maywrite() is defined. (Sorry if
> this has already been discussed before.)
>
> How about vma_is_shared_pt()?
vma_is_mshare() ? ;)
The whole "shared PT / shared PTE" is a bit misleading IMHO and a bit
too dominant in the series. Yes, we're sharing PTEs/page tables, but the
main point is that a single mshare VMA might cover multiple different
VMAs (in a different process).
I would describe mshare VMAs as being something that shares page tables
with another MM, BUT, also that the VMA is a container and what exactly
the *actual* VMAs in there are (including holes), only the owner knows.
E.g., is_vm_hugetlb_page() might be *false* for an mshare VMA, but there
might be hugetlb folios mapped into the page tables, described by a
is_vm_hugetlb_page() VMA in the owner MM.
So again, it's not just "sharing page tables".
--
Cheers,
David / dhildenb
On 10/7/24 3:24 AM, David Hildenbrand wrote:
> On 04.09.24 01:40, James Houghton wrote:
>> On Tue, Sep 3, 2024 at 4:23 PM Anthony Yznaga
>> <anthony.yznaga@oracle.com> wrote:
>>>
>>> From: Khalid Aziz <khalid@kernel.org>
>>>
>>> Add a bit to vm_flags to indicate a vma shares PTEs with others. Add
>>> a function to determine if a vma shares PTEs by checking this flag.
>>> This is to be used to find the shared page table entries on page fault
>>> for vmas sharing PTEs.
>>>
>>> Signed-off-by: Khalid Aziz <khalid@kernel.org>
>>> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
>>> Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
>>> ---
>>> include/linux/mm.h | 7 +++++++
>>> include/trace/events/mmflags.h | 3 +++
>>> mm/internal.h | 5 +++++
>>> 3 files changed, 15 insertions(+)
>>>
>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>> index 6549d0979b28..3aa0b3322284 100644
>>> --- a/include/linux/mm.h
>>> +++ b/include/linux/mm.h
>>> @@ -413,6 +413,13 @@ extern unsigned int kobjsize(const void *objp);
>>> #define VM_DROPPABLE VM_NONE
>>> #endif
>>>
>>> +#ifdef CONFIG_64BIT
>>> +#define VM_SHARED_PT_BIT 41
>>> +#define VM_SHARED_PT BIT(VM_SHARED_PT_BIT)
>>> +#else
>>> +#define VM_SHARED_PT VM_NONE
>>> +#endif
>>> +
>>> #ifdef CONFIG_64BIT
>>> /* VM is sealed, in vm_flags */
>>> #define VM_SEALED _BITUL(63)
>>> diff --git a/include/trace/events/mmflags.h
>>> b/include/trace/events/mmflags.h
>>> index b63d211bd141..e1ae1e60d086 100644
>>> --- a/include/trace/events/mmflags.h
>>> +++ b/include/trace/events/mmflags.h
>>> @@ -167,8 +167,10 @@ IF_HAVE_PG_ARCH_X(arch_3)
>>>
>>> #ifdef CONFIG_64BIT
>>> # define IF_HAVE_VM_DROPPABLE(flag, name) {flag, name},
>>> +# define IF_HAVE_VM_SHARED_PT(flag, name) {flag, name},
>>> #else
>>> # define IF_HAVE_VM_DROPPABLE(flag, name)
>>> +# define IF_HAVE_VM_SHARED_PT(flag, name)
>>> #endif
>>>
>>> #define __def_vmaflag_names \
>>> @@ -204,6 +206,7 @@ IF_HAVE_VM_SOFTDIRTY(VM_SOFTDIRTY,
>>> "softdirty" ) \
>>> {VM_HUGEPAGE, "hugepage" }, \
>>> {VM_NOHUGEPAGE, "nohugepage" }, \
>>> IF_HAVE_VM_DROPPABLE(VM_DROPPABLE, "droppable" ) \
>>> +IF_HAVE_VM_SHARED_PT(VM_SHARED_PT, "sharedpt" ) \
>>> {VM_MERGEABLE, "mergeable" } \
>>>
>>> #define show_vma_flags(flags) \
>>> diff --git a/mm/internal.h b/mm/internal.h
>>> index b4d86436565b..8005d5956b6e 100644
>>> --- a/mm/internal.h
>>> +++ b/mm/internal.h
>>> @@ -1578,4 +1578,9 @@ void unlink_file_vma_batch_init(struct
>>> unlink_vma_file_batch *);
>>> void unlink_file_vma_batch_add(struct unlink_vma_file_batch *,
>>> struct vm_area_struct *);
>>> void unlink_file_vma_batch_final(struct unlink_vma_file_batch *);
>>>
>>
>> Hi Anthony,
>>
>> I'm really excited to see this series on the mailing list again! :) I
>> won't have time to review this series in too much detail, but I hope
>> something like it gets merged eventually.
>>
>>> +static inline bool vma_is_shared(const struct vm_area_struct *vma)
>>> +{
>>> + return VM_SHARED_PT && (vma->vm_flags & VM_SHARED_PT);
>>> +}
>>
>> Tiny comment - I find vma_is_shared() to be a bit of a confusing name,
>> especially given how vma_is_shared_maywrite() is defined. (Sorry if
>> this has already been discussed before.)
>>
>> How about vma_is_shared_pt()?
>
> vma_is_mshare() ? ;)
vma_is_vmas()? :-D
>
> The whole "shared PT / shared PTE" is a bit misleading IMHO and a bit
> too dominant in the series. Yes, we're sharing PTEs/page tables, but
> the main point is that a single mshare VMA might cover multiple
> different VMAs (in a different process).
>
> I would describe mshare VMAs as being something that shares page
> tables with another MM, BUT, also that the VMA is a container and what
> exactly the *actual* VMAs in there are (including holes), only the
> owner knows.
>
> E.g., is_vm_hugetlb_page() might be *false* for an mshare VMA, but
> there might be hugetlb folios mapped into the page tables, described
> by a is_vm_hugetlb_page() VMA in the owner MM.
>
> So again, it's not just "sharing page tables".
Understood. I'm okay with something like vma_is_mshare() or some other
shorthand for a "container" VMA. And I recognize that I need to identify
which code paths need to be enlightened to container VMAs and which
should expect to be operating on a real VMA or don't care.
Anthony
On 9/3/24 4:40 PM, James Houghton wrote:
> On Tue, Sep 3, 2024 at 4:23 PM Anthony Yznaga <anthony.yznaga@oracle.com> wrote:
>> From: Khalid Aziz <khalid@kernel.org>
>>
>> Add a bit to vm_flags to indicate a vma shares PTEs with others. Add
>> a function to determine if a vma shares PTEs by checking this flag.
>> This is to be used to find the shared page table entries on page fault
>> for vmas sharing PTEs.
>>
>> Signed-off-by: Khalid Aziz <khalid@kernel.org>
>> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
>> Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
>> ---
>> include/linux/mm.h | 7 +++++++
>> include/trace/events/mmflags.h | 3 +++
>> mm/internal.h | 5 +++++
>> 3 files changed, 15 insertions(+)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 6549d0979b28..3aa0b3322284 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -413,6 +413,13 @@ extern unsigned int kobjsize(const void *objp);
>> #define VM_DROPPABLE VM_NONE
>> #endif
>>
>> +#ifdef CONFIG_64BIT
>> +#define VM_SHARED_PT_BIT 41
>> +#define VM_SHARED_PT BIT(VM_SHARED_PT_BIT)
>> +#else
>> +#define VM_SHARED_PT VM_NONE
>> +#endif
>> +
>> #ifdef CONFIG_64BIT
>> /* VM is sealed, in vm_flags */
>> #define VM_SEALED _BITUL(63)
>> diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
>> index b63d211bd141..e1ae1e60d086 100644
>> --- a/include/trace/events/mmflags.h
>> +++ b/include/trace/events/mmflags.h
>> @@ -167,8 +167,10 @@ IF_HAVE_PG_ARCH_X(arch_3)
>>
>> #ifdef CONFIG_64BIT
>> # define IF_HAVE_VM_DROPPABLE(flag, name) {flag, name},
>> +# define IF_HAVE_VM_SHARED_PT(flag, name) {flag, name},
>> #else
>> # define IF_HAVE_VM_DROPPABLE(flag, name)
>> +# define IF_HAVE_VM_SHARED_PT(flag, name)
>> #endif
>>
>> #define __def_vmaflag_names \
>> @@ -204,6 +206,7 @@ IF_HAVE_VM_SOFTDIRTY(VM_SOFTDIRTY, "softdirty" ) \
>> {VM_HUGEPAGE, "hugepage" }, \
>> {VM_NOHUGEPAGE, "nohugepage" }, \
>> IF_HAVE_VM_DROPPABLE(VM_DROPPABLE, "droppable" ) \
>> +IF_HAVE_VM_SHARED_PT(VM_SHARED_PT, "sharedpt" ) \
>> {VM_MERGEABLE, "mergeable" } \
>>
>> #define show_vma_flags(flags) \
>> diff --git a/mm/internal.h b/mm/internal.h
>> index b4d86436565b..8005d5956b6e 100644
>> --- a/mm/internal.h
>> +++ b/mm/internal.h
>> @@ -1578,4 +1578,9 @@ void unlink_file_vma_batch_init(struct unlink_vma_file_batch *);
>> void unlink_file_vma_batch_add(struct unlink_vma_file_batch *, struct vm_area_struct *);
>> void unlink_file_vma_batch_final(struct unlink_vma_file_batch *);
>>
Hi James,
> Hi Anthony,
>
> I'm really excited to see this series on the mailing list again! :) I
> won't have time to review this series in too much detail, but I hope
> something like it gets merged eventually.
Me, too. :-)
>
>> +static inline bool vma_is_shared(const struct vm_area_struct *vma)
>> +{
>> + return VM_SHARED_PT && (vma->vm_flags & VM_SHARED_PT);
>> +}
> Tiny comment - I find vma_is_shared() to be a bit of a confusing name,
> especially given how vma_is_shared_maywrite() is defined. (Sorry if
> this has already been discussed before.)
>
> How about vma_is_shared_pt()?
Good point. I'll make this change. Thanks for taking a look.
Anthony
© 2016 - 2025 Red Hat, Inc.