Re: [PATCH 05/13] mm/frame-vector: Use FOLL_LONGTERM
On Wed, Oct 7, 2020 at 11:13 PM John Hubbard wrote:
>
> On 10/7/20 9:44 AM, Daniel Vetter wrote:
> > This is used by media/videbuf2 for persistent dma mappings, not just
> > for a single dma operation and then freed again, so needs
> > FOLL_LONGTERM.
> >
> > Unfortunately current pup_locked doesn't support FOLL_LONGTERM due to
> > locking issues. Rework the code to pull the pup path out from the
> > mmap_sem critical section as suggested by Jason.
> >
> > Signed-off-by: Daniel Vetter
> > Cc: Jason Gunthorpe
> > Cc: Pawel Osciak
> > Cc: Marek Szyprowski
> > Cc: Kyungmin Park
> > Cc: Tomasz Figa
> > Cc: Mauro Carvalho Chehab
> > Cc: Andrew Morton
> > Cc: John Hubbard
> > Cc: Jérôme Glisse
> > Cc: Jan Kara
> > Cc: Dan Williams
> > Cc: linux...@kvack.org
> > Cc: linux-arm-ker...@lists.infradead.org
> > Cc: linux-samsung-...@vger.kernel.org
> > Cc: linux-me...@vger.kernel.org
> > ---
> > mm/frame_vector.c | 36 +++-
> > 1 file changed, 11 insertions(+), 25 deletions(-)
> >
> > diff --git a/mm/frame_vector.c b/mm/frame_vector.c
> > index 10f82d5643b6..39db520a51dc 100644
> > --- a/mm/frame_vector.c
> > +++ b/mm/frame_vector.c
> > @@ -38,7 +38,6 @@ int get_vaddr_frames(unsigned long start, unsigned int
> > nr_frames,
> > struct vm_area_struct *vma;
> > int ret = 0;
> > int err;
> > - int locked;
> >
> > if (nr_frames == 0)
> > return 0;
> > @@ -48,35 +47,22 @@ int get_vaddr_frames(unsigned long start, unsigned int
> > nr_frames,
> >
> > start = untagged_addr(start);
> >
> > + ret = pin_user_pages_fast(start, nr_frames,
> > + FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM,
> > + (struct page **)(vec->ptrs));
> > + if (ret > 0) {
> > + vec->got_ref = true;
> > + vec->is_pfns = false;
> > + goto out_unlocked;
> > + }
>
> This part looks good, and changing to _fast is a potential performance
> improvement,
> too.
>
> > +
> > mmap_read_lock(mm);
> > - locked = 1;
> > vma = find_vma_intersection(mm, start, start + 1);
> > if (!vma) {
> > ret = -EFAULT;
> > goto out;
> > }
> >
> > - /*
> > - * While get_vaddr_frames() could be used for transient (kernel
> > - * controlled lifetime) pinning of memory pages all current
> > - * users establish long term (userspace controlled lifetime)
> > - * page pinning. Treat get_vaddr_frames() like
> > - * get_user_pages_longterm() and disallow it for filesystem-dax
> > - * mappings.
> > - */
> > - if (vma_is_fsdax(vma)) {
> > - ret = -EOPNOTSUPP;
> > - goto out;
> > - }
>
> Are you sure we don't need to check vma_is_fsdax() anymore?
Since FOLL_LONGTERM checks for this and can only return struct page
backed memory, and explicitly excludes VM_IO | VM_PFNMAP, was assuming
this is not needed for follow_pfn. And the get_user_pages_locked this
used back then didn't have the same check, hence why it was added (and
FOLL_LONGTERM still doesn't work for the _locked versions, as you
pointed out on the last round of this discussion).
But now that you're asking, I have no idea whether fsdax vma can also
be of VM_IO | VM_PFNMAP type. I'm not seeing that set anywhere in
fs/dax.c, but that says nothing :-)
Dan, you added this check originally, do we need it for VM_SPECIAL vmas too?
Thanks, Daniel
>
> > -
> > - if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
> > - vec->got_ref = true;
> > - vec->is_pfns = false;
> > - ret = pin_user_pages_locked(start, nr_frames,
> > - gup_flags, (struct page **)(vec->ptrs), &locked);
> > - goto out;
> > - }
> > -
> > vec->got_ref = false;
> > vec->is_pfns = true;
> > do {
> > @@ -101,8 +87,8 @@ int get_vaddr_frames(unsigned long start, unsigned int
> > nr_frames,
> > vma = find_vma_intersection(mm, start, start + 1);
> > } while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP));
> > out:
> > - if (locked)
> > - mmap_read_unlock(mm);
> > + mmap_read_unlock(mm);
> > +out_unlocked:
> > if (!ret)
> > ret = -EFAULT;
> > if (ret > 0)
> >
>
> All of the error handling still looks accurate there.
>
> thanks,
> --
> John Hubbard
> NVIDIA
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
Re: [PATCH 05/13] mm/frame-vector: Use FOLL_LONGTERM
On 10/7/20 9:44 AM, Daniel Vetter wrote:
This is used by media/videbuf2 for persistent dma mappings, not just
for a single dma operation and then freed again, so needs
FOLL_LONGTERM.
Unfortunately current pup_locked doesn't support FOLL_LONGTERM due to
locking issues. Rework the code to pull the pup path out from the
mmap_sem critical section as suggested by Jason.
Signed-off-by: Daniel Vetter
Cc: Jason Gunthorpe
Cc: Pawel Osciak
Cc: Marek Szyprowski
Cc: Kyungmin Park
Cc: Tomasz Figa
Cc: Mauro Carvalho Chehab
Cc: Andrew Morton
Cc: John Hubbard
Cc: Jérôme Glisse
Cc: Jan Kara
Cc: Dan Williams
Cc: linux...@kvack.org
Cc: linux-arm-ker...@lists.infradead.org
Cc: linux-samsung-...@vger.kernel.org
Cc: linux-me...@vger.kernel.org
---
mm/frame_vector.c | 36 +++-
1 file changed, 11 insertions(+), 25 deletions(-)
diff --git a/mm/frame_vector.c b/mm/frame_vector.c
index 10f82d5643b6..39db520a51dc 100644
--- a/mm/frame_vector.c
+++ b/mm/frame_vector.c
@@ -38,7 +38,6 @@ int get_vaddr_frames(unsigned long start, unsigned int
nr_frames,
struct vm_area_struct *vma;
int ret = 0;
int err;
- int locked;
if (nr_frames == 0)
return 0;
@@ -48,35 +47,22 @@ int get_vaddr_frames(unsigned long start, unsigned int
nr_frames,
start = untagged_addr(start);
+ ret = pin_user_pages_fast(start, nr_frames,
+ FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM,
+ (struct page **)(vec->ptrs));
+ if (ret > 0) {
+ vec->got_ref = true;
+ vec->is_pfns = false;
+ goto out_unlocked;
+ }
This part looks good, and changing to _fast is a potential performance
improvement,
too.
+
mmap_read_lock(mm);
- locked = 1;
vma = find_vma_intersection(mm, start, start + 1);
if (!vma) {
ret = -EFAULT;
goto out;
}
- /*
-* While get_vaddr_frames() could be used for transient (kernel
-* controlled lifetime) pinning of memory pages all current
-* users establish long term (userspace controlled lifetime)
-* page pinning. Treat get_vaddr_frames() like
-* get_user_pages_longterm() and disallow it for filesystem-dax
-* mappings.
-*/
- if (vma_is_fsdax(vma)) {
- ret = -EOPNOTSUPP;
- goto out;
- }
Are you sure we don't need to check vma_is_fsdax() anymore?
-
- if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
- vec->got_ref = true;
- vec->is_pfns = false;
- ret = pin_user_pages_locked(start, nr_frames,
- gup_flags, (struct page **)(vec->ptrs), &locked);
- goto out;
- }
-
vec->got_ref = false;
vec->is_pfns = true;
do {
@@ -101,8 +87,8 @@ int get_vaddr_frames(unsigned long start, unsigned int
nr_frames,
vma = find_vma_intersection(mm, start, start + 1);
} while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP));
out:
- if (locked)
- mmap_read_unlock(mm);
+ mmap_read_unlock(mm);
+out_unlocked:
if (!ret)
ret = -EFAULT;
if (ret > 0)
All of the error handling still looks accurate there.
thanks,
--
John Hubbard
NVIDIA
Re: [PATCH 05/13] mm/frame-vector: Use FOLL_LONGTERM
On Wed, Oct 07, 2020 at 07:12:24PM +0200, Daniel Vetter wrote:
> On Wed, Oct 7, 2020 at 6:53 PM Jason Gunthorpe wrote:
> >
> > On Wed, Oct 07, 2020 at 06:44:18PM +0200, Daniel Vetter wrote:
> > >
> > > - /*
> > > - * While get_vaddr_frames() could be used for transient (kernel
> > > - * controlled lifetime) pinning of memory pages all current
> > > - * users establish long term (userspace controlled lifetime)
> > > - * page pinning. Treat get_vaddr_frames() like
> > > - * get_user_pages_longterm() and disallow it for filesystem-dax
> > > - * mappings.
> > > - */
> > > - if (vma_is_fsdax(vma)) {
> > > - ret = -EOPNOTSUPP;
> > > - goto out;
> > > - }
> > > -
> > > - if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
> > > - vec->got_ref = true;
> > > - vec->is_pfns = false;
> > > - ret = pin_user_pages_locked(start, nr_frames,
> > > - gup_flags, (struct page **)(vec->ptrs), &locked);
> > > - goto out;
> > > - }
> >
> > The vm_flags still need to be checked before going into the while
> > loop. If the break is taken then nothing would check vm_flags
>
> Hm right that's a bin inconsistent. follow_pfn also checks for this,
> so I think we can just ditch this entirely both here and in the do {}
> while () check, simplifying the latter to just while (vma). Well, just
> make it a real loop with less confusing control flow probably.
It does read very poorly with the redundant check, espeically since I
keep forgetting follow_pfn does it too :\
Jason
Re: [PATCH 05/13] mm/frame-vector: Use FOLL_LONGTERM
On Wed, Oct 7, 2020 at 6:53 PM Jason Gunthorpe wrote:
>
> On Wed, Oct 07, 2020 at 06:44:18PM +0200, Daniel Vetter wrote:
> >
> > - /*
> > - * While get_vaddr_frames() could be used for transient (kernel
> > - * controlled lifetime) pinning of memory pages all current
> > - * users establish long term (userspace controlled lifetime)
> > - * page pinning. Treat get_vaddr_frames() like
> > - * get_user_pages_longterm() and disallow it for filesystem-dax
> > - * mappings.
> > - */
> > - if (vma_is_fsdax(vma)) {
> > - ret = -EOPNOTSUPP;
> > - goto out;
> > - }
> > -
> > - if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
> > - vec->got_ref = true;
> > - vec->is_pfns = false;
> > - ret = pin_user_pages_locked(start, nr_frames,
> > - gup_flags, (struct page **)(vec->ptrs), &locked);
> > - goto out;
> > - }
>
> The vm_flags still need to be checked before going into the while
> loop. If the break is taken then nothing would check vm_flags
Hm right that's a bin inconsistent. follow_pfn also checks for this,
so I think we can just ditch this entirely both here and in the do {}
while () check, simplifying the latter to just while (vma). Well, just
make it a real loop with less confusing control flow probably.
Or prefer I keep this and touch the code less?
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
Re: [PATCH 05/13] mm/frame-vector: Use FOLL_LONGTERM
On Wed, Oct 07, 2020 at 06:44:18PM +0200, Daniel Vetter wrote:
>
> - /*
> - * While get_vaddr_frames() could be used for transient (kernel
> - * controlled lifetime) pinning of memory pages all current
> - * users establish long term (userspace controlled lifetime)
> - * page pinning. Treat get_vaddr_frames() like
> - * get_user_pages_longterm() and disallow it for filesystem-dax
> - * mappings.
> - */
> - if (vma_is_fsdax(vma)) {
> - ret = -EOPNOTSUPP;
> - goto out;
> - }
> -
> - if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
> - vec->got_ref = true;
> - vec->is_pfns = false;
> - ret = pin_user_pages_locked(start, nr_frames,
> - gup_flags, (struct page **)(vec->ptrs), &locked);
> - goto out;
> - }
The vm_flags still need to be checked before going into the while
loop. If the break is taken then nothing would check vm_flags
Jason
[PATCH 05/13] mm/frame-vector: Use FOLL_LONGTERM
This is used by media/videbuf2 for persistent dma mappings, not just
for a single dma operation and then freed again, so needs
FOLL_LONGTERM.
Unfortunately current pup_locked doesn't support FOLL_LONGTERM due to
locking issues. Rework the code to pull the pup path out from the
mmap_sem critical section as suggested by Jason.
Signed-off-by: Daniel Vetter
Cc: Jason Gunthorpe
Cc: Pawel Osciak
Cc: Marek Szyprowski
Cc: Kyungmin Park
Cc: Tomasz Figa
Cc: Mauro Carvalho Chehab
Cc: Andrew Morton
Cc: John Hubbard
Cc: Jérôme Glisse
Cc: Jan Kara
Cc: Dan Williams
Cc: linux...@kvack.org
Cc: linux-arm-ker...@lists.infradead.org
Cc: linux-samsung-...@vger.kernel.org
Cc: linux-me...@vger.kernel.org
---
mm/frame_vector.c | 36 +++-
1 file changed, 11 insertions(+), 25 deletions(-)
diff --git a/mm/frame_vector.c b/mm/frame_vector.c
index 10f82d5643b6..39db520a51dc 100644
--- a/mm/frame_vector.c
+++ b/mm/frame_vector.c
@@ -38,7 +38,6 @@ int get_vaddr_frames(unsigned long start, unsigned int
nr_frames,
struct vm_area_struct *vma;
int ret = 0;
int err;
- int locked;
if (nr_frames == 0)
return 0;
@@ -48,35 +47,22 @@ int get_vaddr_frames(unsigned long start, unsigned int
nr_frames,
start = untagged_addr(start);
+ ret = pin_user_pages_fast(start, nr_frames,
+ FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM,
+ (struct page **)(vec->ptrs));
+ if (ret > 0) {
+ vec->got_ref = true;
+ vec->is_pfns = false;
+ goto out_unlocked;
+ }
+
mmap_read_lock(mm);
- locked = 1;
vma = find_vma_intersection(mm, start, start + 1);
if (!vma) {
ret = -EFAULT;
goto out;
}
- /*
-* While get_vaddr_frames() could be used for transient (kernel
-* controlled lifetime) pinning of memory pages all current
-* users establish long term (userspace controlled lifetime)
-* page pinning. Treat get_vaddr_frames() like
-* get_user_pages_longterm() and disallow it for filesystem-dax
-* mappings.
-*/
- if (vma_is_fsdax(vma)) {
- ret = -EOPNOTSUPP;
- goto out;
- }
-
- if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
- vec->got_ref = true;
- vec->is_pfns = false;
- ret = pin_user_pages_locked(start, nr_frames,
- gup_flags, (struct page **)(vec->ptrs), &locked);
- goto out;
- }
-
vec->got_ref = false;
vec->is_pfns = true;
do {
@@ -101,8 +87,8 @@ int get_vaddr_frames(unsigned long start, unsigned int
nr_frames,
vma = find_vma_intersection(mm, start, start + 1);
} while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP));
out:
- if (locked)
- mmap_read_unlock(mm);
+ mmap_read_unlock(mm);
+out_unlocked:
if (!ret)
ret = -EFAULT;
if (ret > 0)
--
2.28.0
