For hugely mapped thp, we use is_huge_zero_pmd() to check if it's
zero page or not.
We do fill ptes with my_zero_pfn() when we split zero thp pmd, but
this is not what we have in vm_normal_page_pmd().
pmd_trans_huge_lock() makes sure of it.
This is a trivial fix for /proc/pid/numa_maps, and AFAIK nobody
complains about it.
Signed-off-by: Yu Zhao <[email protected]>
---
mm/memory.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/memory.c b/mm/memory.c
index e2bb51b6242e..ea3c74855b23 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -654,7 +654,7 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
if (pmd_devmap(pmd))
return NULL;
- if (is_zero_pfn(pfn))
+ if (is_huge_zero_pmd(pmd))
return NULL;
if (unlikely(pfn > highest_memmap_pfn))
return NULL;
--
2.23.0.187.g17f5b7556c-goog
Why did you not cc Gerald who wrote the patch? You can't just
run get_maintainers.pl and call it good.
On Sun, Aug 25, 2019 at 02:06:21PM -0600, Yu Zhao wrote:
> For hugely mapped thp, we use is_huge_zero_pmd() to check if it's
> zero page or not.
>
> We do fill ptes with my_zero_pfn() when we split zero thp pmd, but
> this is not what we have in vm_normal_page_pmd().
> pmd_trans_huge_lock() makes sure of it.
>
> This is a trivial fix for /proc/pid/numa_maps, and AFAIK nobody
> complains about it.
>
> Signed-off-by: Yu Zhao <[email protected]>
> ---
> mm/memory.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index e2bb51b6242e..ea3c74855b23 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -654,7 +654,7 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
>
> if (pmd_devmap(pmd))
> return NULL;
> - if (is_zero_pfn(pfn))
> + if (is_huge_zero_pmd(pmd))
> return NULL;
> if (unlikely(pfn > highest_memmap_pfn))
> return NULL;
> --
> 2.23.0.187.g17f5b7556c-goog
>
On Mon, 26 Aug 2019 06:18:58 -0700
Matthew Wilcox <[email protected]> wrote:
> Why did you not cc Gerald who wrote the patch? You can't just
> run get_maintainers.pl and call it good.
>
> On Sun, Aug 25, 2019 at 02:06:21PM -0600, Yu Zhao wrote:
> > For hugely mapped thp, we use is_huge_zero_pmd() to check if it's
> > zero page or not.
> >
> > We do fill ptes with my_zero_pfn() when we split zero thp pmd, but
> > this is not what we have in vm_normal_page_pmd().
> > pmd_trans_huge_lock() makes sure of it.
> >
> > This is a trivial fix for /proc/pid/numa_maps, and AFAIK nobody
> > complains about it.
> >
> > Signed-off-by: Yu Zhao <[email protected]>
> > ---
> > mm/memory.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/mm/memory.c b/mm/memory.c
> > index e2bb51b6242e..ea3c74855b23 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -654,7 +654,7 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
> >
> > if (pmd_devmap(pmd))
> > return NULL;
> > - if (is_zero_pfn(pfn))
> > + if (is_huge_zero_pmd(pmd))
> > return NULL;
> > if (unlikely(pfn > highest_memmap_pfn))
> > return NULL;
> > --
> > 2.23.0.187.g17f5b7556c-goog
> >
Looks good to me. The "_pmd" versions for can_gather_numa_stats() and
vm_normal_page() were introduced to avoid using pte_present/dirty() on
pmds, which is not affected by this patch.
In fact, for vm_normal_page_pmd() I basically copied most of the code
from vm_normal_page(), including the is_zero_pfn(pfn) check, which does
look wrong to me now. Using is_huge_zero_pmd() should be correct.
Maybe the description could also mention the symptom of this bug?
I would assume that it affects anon/dirty accounting in gather_pte_stats(),
for huge mappings, if zero page mappings are not correctly recognized.
Regards,
Gerald
On Mon, Aug 26, 2019 at 05:09:34PM +0200, Gerald Schaefer wrote:
> On Mon, 26 Aug 2019 06:18:58 -0700
> Matthew Wilcox <[email protected]> wrote:
>
> > Why did you not cc Gerald who wrote the patch? You can't just
> > run get_maintainers.pl and call it good.
> >
> > On Sun, Aug 25, 2019 at 02:06:21PM -0600, Yu Zhao wrote:
> > > For hugely mapped thp, we use is_huge_zero_pmd() to check if it's
> > > zero page or not.
> > >
> > > We do fill ptes with my_zero_pfn() when we split zero thp pmd, but
> > > this is not what we have in vm_normal_page_pmd().
> > > pmd_trans_huge_lock() makes sure of it.
> > >
> > > This is a trivial fix for /proc/pid/numa_maps, and AFAIK nobody
> > > complains about it.
> > >
> > > Signed-off-by: Yu Zhao <[email protected]>
> > > ---
> > > mm/memory.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/mm/memory.c b/mm/memory.c
> > > index e2bb51b6242e..ea3c74855b23 100644
> > > --- a/mm/memory.c
> > > +++ b/mm/memory.c
> > > @@ -654,7 +654,7 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
> > >
> > > if (pmd_devmap(pmd))
> > > return NULL;
> > > - if (is_zero_pfn(pfn))
> > > + if (is_huge_zero_pmd(pmd))
> > > return NULL;
> > > if (unlikely(pfn > highest_memmap_pfn))
> > > return NULL;
> > > --
> > > 2.23.0.187.g17f5b7556c-goog
> > >
>
> Looks good to me. The "_pmd" versions for can_gather_numa_stats() and
> vm_normal_page() were introduced to avoid using pte_present/dirty() on
> pmds, which is not affected by this patch.
>
> In fact, for vm_normal_page_pmd() I basically copied most of the code
> from vm_normal_page(), including the is_zero_pfn(pfn) check, which does
> look wrong to me now. Using is_huge_zero_pmd() should be correct.
>
> Maybe the description could also mention the symptom of this bug?
> I would assume that it affects anon/dirty accounting in gather_pte_stats(),
> for huge mappings, if zero page mappings are not correctly recognized.
Hi, sorry for not copying you on the original email. I came across
this while I was looking at the code. I'm not aware of any symptom.
Thank you.
For hugely mapped thp, we use is_huge_zero_pmd() to check if it's
zero page or not.
We do fill ptes with my_zero_pfn() when we split zero thp pmd, but
this is not what we have in vm_normal_page_pmd() --
pmd_trans_huge_lock() makes sure of it.
This is a trivial fix for /proc/pid/numa_maps, and AFAIK nobody
complains about it.
Gerald Schaefer asked:
> Maybe the description could also mention the symptom of this bug?
> I would assume that it affects anon/dirty accounting in gather_pte_stats(),
> for huge mappings, if zero page mappings are not correctly recognized.
I came across this while I was looking at the code, so I'm not aware of
any symptom.
Signed-off-by: Yu Zhao <[email protected]>
---
mm/memory.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/memory.c b/mm/memory.c
index b1ca51a079f2..cf209f84ce4a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -654,7 +654,7 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
if (pmd_devmap(pmd))
return NULL;
- if (is_zero_pfn(pfn))
+ if (is_huge_zero_pmd(pmd))
return NULL;
if (unlikely(pfn > highest_memmap_pfn))
return NULL;
--
2.24.0.rc1.363.gb1bccd3e3d-goog