Re: [PATCH 3.10 060/268] xen/gntdev: Use VM_MIXEDMAP instead of VM_IO to avoid NUMA balancing

[Willy Tarreau]

On Mon, Jun 19, 2017 at 07:57:27PM -0700, Hugh Dickins wrote:
> On Mon, 19 Jun 2017, Willy Tarreau wrote:
> 
> > From: Boris Ostrovsky 
> > 
> > commit 30faaafdfa0c754c91bac60f216c9f34a2bfdf7e upstream.
> > 
> > Commit 9c17d96500f7 ("xen/gntdev: Grant maps should not be subject to
> > NUMA balancing") set VM_IO flag to prevent grant maps from being
> > subjected to NUMA balancing.
> > 
> > It was discovered recently that this flag causes get_user_pages() to
> > always fail with -EFAULT.
> > 
> > check_vma_flags
> > __get_user_pages
> > __get_user_pages_locked
> > __get_user_pages_unlocked
> > get_user_pages_fast
> > iov_iter_get_pages
> > dio_refill_pages
> > do_direct_IO
> > do_blockdev_direct_IO
> > do_blockdev_direct_IO
> > ext4_direct_IO_read
> > generic_file_read_iter
> > aio_run_iocb
> > 
> > (which can happen if guest's vdisk has direct-io-safe option).
> > 
> > To avoid this let's use VM_MIXEDMAP flag instead --- it prevents
> > NUMA balancing just as VM_IO does and has no effect on
> > check_vma_flags().
> 
> This is only valid if kernel/sched/fair.c is checking for VM_MIXEDMAP,
> and that came in v4.1's 8e76d4eecf7a ("sched, numa: do not hint for
> NUMA balancing on VM_MIXEDMAP mappings"), which I don't see in your
> tree nor in this series (please double check, I may have missed it).
> 
> It would be good to have that one in too, and it was marked for
> stable; but maybe it didn't apply, because of depending on another
> commit adding the is_vm_hugetlb_page(vma) check there?  Which I
> expect would also be good to have, but I haven't looked it up.
> 
> Maybe drop this one for this round, and gather up its dependencies
> for the next round.

Yep that's what I'm going to do, thanks for the details. I've found
that I'll simply have to pick 6b79c57b92 and 8e76d4eecf. I won't
take the onse adding vma_policy_mof() that late in the cycle as
apparently it's only about a performance regression.

> Ben's 3.16 tree appeared to be in the same position,
> I didn't look at the EOL 3.18.

I picked this one by reviewing what patches from 3.12 were missing in
3.10 and 3.12 had the same issue. We've probably lost this along the
chain of backports.

> (I've not yet checked through backports of the "larger stack guard gap"
> - thank you all for those - will do so, but won't get through them
> tonight - I must look into DaveJ's trinity VM_BUG_ON now.)

No pb, you're welcome. At least they didn't prevent Guenter's machines
from booting on 82 platforms, which is a good start ;-)

Willy

Re: [PATCH 3.10 060/268] xen/gntdev: Use VM_MIXEDMAP instead of VM_IO to avoid NUMA balancing

[Willy Tarreau]

On Mon, Jun 19, 2017 at 07:57:27PM -0700, Hugh Dickins wrote:
> On Mon, 19 Jun 2017, Willy Tarreau wrote:
> 
> > From: Boris Ostrovsky 
> > 
> > commit 30faaafdfa0c754c91bac60f216c9f34a2bfdf7e upstream.
> > 
> > Commit 9c17d96500f7 ("xen/gntdev: Grant maps should not be subject to
> > NUMA balancing") set VM_IO flag to prevent grant maps from being
> > subjected to NUMA balancing.
> > 
> > It was discovered recently that this flag causes get_user_pages() to
> > always fail with -EFAULT.
> > 
> > check_vma_flags
> > __get_user_pages
> > __get_user_pages_locked
> > __get_user_pages_unlocked
> > get_user_pages_fast
> > iov_iter_get_pages
> > dio_refill_pages
> > do_direct_IO
> > do_blockdev_direct_IO
> > do_blockdev_direct_IO
> > ext4_direct_IO_read
> > generic_file_read_iter
> > aio_run_iocb
> > 
> > (which can happen if guest's vdisk has direct-io-safe option).
> > 
> > To avoid this let's use VM_MIXEDMAP flag instead --- it prevents
> > NUMA balancing just as VM_IO does and has no effect on
> > check_vma_flags().
> 
> This is only valid if kernel/sched/fair.c is checking for VM_MIXEDMAP,
> and that came in v4.1's 8e76d4eecf7a ("sched, numa: do not hint for
> NUMA balancing on VM_MIXEDMAP mappings"), which I don't see in your
> tree nor in this series (please double check, I may have missed it).
> 
> It would be good to have that one in too, and it was marked for
> stable; but maybe it didn't apply, because of depending on another
> commit adding the is_vm_hugetlb_page(vma) check there?  Which I
> expect would also be good to have, but I haven't looked it up.
> 
> Maybe drop this one for this round, and gather up its dependencies
> for the next round.

Yep that's what I'm going to do, thanks for the details. I've found
that I'll simply have to pick 6b79c57b92 and 8e76d4eecf. I won't
take the onse adding vma_policy_mof() that late in the cycle as
apparently it's only about a performance regression.

> Ben's 3.16 tree appeared to be in the same position,
> I didn't look at the EOL 3.18.

I picked this one by reviewing what patches from 3.12 were missing in
3.10 and 3.12 had the same issue. We've probably lost this along the
chain of backports.

> (I've not yet checked through backports of the "larger stack guard gap"
> - thank you all for those - will do so, but won't get through them
> tonight - I must look into DaveJ's trinity VM_BUG_ON now.)

No pb, you're welcome. At least they didn't prevent Guenter's machines
from booting on 82 platforms, which is a good start ;-)

Willy

Re: [PATCH 3.10 060/268] xen/gntdev: Use VM_MIXEDMAP instead of VM_IO to avoid NUMA balancing

[Hugh Dickins]

On Mon, 19 Jun 2017, Willy Tarreau wrote:

> From: Boris Ostrovsky 
> 
> commit 30faaafdfa0c754c91bac60f216c9f34a2bfdf7e upstream.
> 
> Commit 9c17d96500f7 ("xen/gntdev: Grant maps should not be subject to
> NUMA balancing") set VM_IO flag to prevent grant maps from being
> subjected to NUMA balancing.
> 
> It was discovered recently that this flag causes get_user_pages() to
> always fail with -EFAULT.
> 
> check_vma_flags
> __get_user_pages
> __get_user_pages_locked
> __get_user_pages_unlocked
> get_user_pages_fast
> iov_iter_get_pages
> dio_refill_pages
> do_direct_IO
> do_blockdev_direct_IO
> do_blockdev_direct_IO
> ext4_direct_IO_read
> generic_file_read_iter
> aio_run_iocb
> 
> (which can happen if guest's vdisk has direct-io-safe option).
> 
> To avoid this let's use VM_MIXEDMAP flag instead --- it prevents
> NUMA balancing just as VM_IO does and has no effect on
> check_vma_flags().

This is only valid if kernel/sched/fair.c is checking for VM_MIXEDMAP,
and that came in v4.1's 8e76d4eecf7a ("sched, numa: do not hint for
NUMA balancing on VM_MIXEDMAP mappings"), which I don't see in your
tree nor in this series (please double check, I may have missed it).

It would be good to have that one in too, and it was marked for
stable; but maybe it didn't apply, because of depending on another
commit adding the is_vm_hugetlb_page(vma) check there?  Which I
expect would also be good to have, but I haven't looked it up.

Maybe drop this one for this round, and gather up its dependencies
for the next round.

Ben's 3.16 tree appeared to be in the same position,
I didn't look at the EOL 3.18.

(I've not yet checked through backports of the "larger stack guard gap"
- thank you all for those - will do so, but won't get through them
tonight - I must look into DaveJ's trinity VM_BUG_ON now.)

Hugh

> 
> Reported-by: Olaf Hering 
> Suggested-by: Hugh Dickins 
> Signed-off-by: Boris Ostrovsky 
> Acked-by: Hugh Dickins 
> Tested-by: Olaf Hering 
> Signed-off-by: Juergen Gross 
> Signed-off-by: Willy Tarreau 
> ---
>  drivers/xen/gntdev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index 3d8e609..6c6d253 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -770,7 +770,7 @@ static int gntdev_mmap(struct file *flip, struct 
> vm_area_struct *vma)
>  
>   vma->vm_ops = _vmops;
>  
> - vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_IO;
> + vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_MIXEDMAP;
>  
>   if (use_ptemod)
>   vma->vm_flags |= VM_DONTCOPY;
> -- 
> 2.8.0.rc2.1.gbe9624a

Re: [PATCH 3.10 060/268] xen/gntdev: Use VM_MIXEDMAP instead of VM_IO to avoid NUMA balancing

[Hugh Dickins]

On Mon, 19 Jun 2017, Willy Tarreau wrote:

> From: Boris Ostrovsky 
> 
> commit 30faaafdfa0c754c91bac60f216c9f34a2bfdf7e upstream.
> 
> Commit 9c17d96500f7 ("xen/gntdev: Grant maps should not be subject to
> NUMA balancing") set VM_IO flag to prevent grant maps from being
> subjected to NUMA balancing.
> 
> It was discovered recently that this flag causes get_user_pages() to
> always fail with -EFAULT.
> 
> check_vma_flags
> __get_user_pages
> __get_user_pages_locked
> __get_user_pages_unlocked
> get_user_pages_fast
> iov_iter_get_pages
> dio_refill_pages
> do_direct_IO
> do_blockdev_direct_IO
> do_blockdev_direct_IO
> ext4_direct_IO_read
> generic_file_read_iter
> aio_run_iocb
> 
> (which can happen if guest's vdisk has direct-io-safe option).
> 
> To avoid this let's use VM_MIXEDMAP flag instead --- it prevents
> NUMA balancing just as VM_IO does and has no effect on
> check_vma_flags().

This is only valid if kernel/sched/fair.c is checking for VM_MIXEDMAP,
and that came in v4.1's 8e76d4eecf7a ("sched, numa: do not hint for
NUMA balancing on VM_MIXEDMAP mappings"), which I don't see in your
tree nor in this series (please double check, I may have missed it).

It would be good to have that one in too, and it was marked for
stable; but maybe it didn't apply, because of depending on another
commit adding the is_vm_hugetlb_page(vma) check there?  Which I
expect would also be good to have, but I haven't looked it up.

Maybe drop this one for this round, and gather up its dependencies
for the next round.

Ben's 3.16 tree appeared to be in the same position,
I didn't look at the EOL 3.18.

(I've not yet checked through backports of the "larger stack guard gap"
- thank you all for those - will do so, but won't get through them
tonight - I must look into DaveJ's trinity VM_BUG_ON now.)

Hugh

> 
> Reported-by: Olaf Hering 
> Suggested-by: Hugh Dickins 
> Signed-off-by: Boris Ostrovsky 
> Acked-by: Hugh Dickins 
> Tested-by: Olaf Hering 
> Signed-off-by: Juergen Gross 
> Signed-off-by: Willy Tarreau 
> ---
>  drivers/xen/gntdev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index 3d8e609..6c6d253 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -770,7 +770,7 @@ static int gntdev_mmap(struct file *flip, struct 
> vm_area_struct *vma)
>  
>   vma->vm_ops = _vmops;
>  
> - vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_IO;
> + vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_MIXEDMAP;
>  
>   if (use_ptemod)
>   vma->vm_flags |= VM_DONTCOPY;
> -- 
> 2.8.0.rc2.1.gbe9624a

[PATCH 3.10 060/268] xen/gntdev: Use VM_MIXEDMAP instead of VM_IO to avoid NUMA balancing

[Willy Tarreau]

From: Boris Ostrovsky 

commit 30faaafdfa0c754c91bac60f216c9f34a2bfdf7e upstream.

Commit 9c17d96500f7 ("xen/gntdev: Grant maps should not be subject to
NUMA balancing") set VM_IO flag to prevent grant maps from being
subjected to NUMA balancing.

It was discovered recently that this flag causes get_user_pages() to
always fail with -EFAULT.

check_vma_flags
__get_user_pages
__get_user_pages_locked
__get_user_pages_unlocked
get_user_pages_fast
iov_iter_get_pages
dio_refill_pages
do_direct_IO
do_blockdev_direct_IO
do_blockdev_direct_IO
ext4_direct_IO_read
generic_file_read_iter
aio_run_iocb

(which can happen if guest's vdisk has direct-io-safe option).

To avoid this let's use VM_MIXEDMAP flag instead --- it prevents
NUMA balancing just as VM_IO does and has no effect on
check_vma_flags().

Reported-by: Olaf Hering 
Suggested-by: Hugh Dickins 
Signed-off-by: Boris Ostrovsky 
Acked-by: Hugh Dickins 
Tested-by: Olaf Hering 
Signed-off-by: Juergen Gross 
Signed-off-by: Willy Tarreau 
---
 drivers/xen/gntdev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 3d8e609..6c6d253 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -770,7 +770,7 @@ static int gntdev_mmap(struct file *flip, struct 
vm_area_struct *vma)
 
vma->vm_ops = _vmops;
 
-   vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_IO;
+   vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_MIXEDMAP;
 
if (use_ptemod)
vma->vm_flags |= VM_DONTCOPY;
-- 
2.8.0.rc2.1.gbe9624a

[PATCH 3.10 060/268] xen/gntdev: Use VM_MIXEDMAP instead of VM_IO to avoid NUMA balancing

[Willy Tarreau]

From: Boris Ostrovsky 

commit 30faaafdfa0c754c91bac60f216c9f34a2bfdf7e upstream.

Commit 9c17d96500f7 ("xen/gntdev: Grant maps should not be subject to
NUMA balancing") set VM_IO flag to prevent grant maps from being
subjected to NUMA balancing.

It was discovered recently that this flag causes get_user_pages() to
always fail with -EFAULT.

check_vma_flags
__get_user_pages
__get_user_pages_locked
__get_user_pages_unlocked
get_user_pages_fast
iov_iter_get_pages
dio_refill_pages
do_direct_IO
do_blockdev_direct_IO
do_blockdev_direct_IO
ext4_direct_IO_read
generic_file_read_iter
aio_run_iocb

(which can happen if guest's vdisk has direct-io-safe option).

To avoid this let's use VM_MIXEDMAP flag instead --- it prevents
NUMA balancing just as VM_IO does and has no effect on
check_vma_flags().

Reported-by: Olaf Hering 
Suggested-by: Hugh Dickins 
Signed-off-by: Boris Ostrovsky 
Acked-by: Hugh Dickins 
Tested-by: Olaf Hering 
Signed-off-by: Juergen Gross 
Signed-off-by: Willy Tarreau 
---
 drivers/xen/gntdev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 3d8e609..6c6d253 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -770,7 +770,7 @@ static int gntdev_mmap(struct file *flip, struct 
vm_area_struct *vma)
 
vma->vm_ops = _vmops;
 
-   vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_IO;
+   vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_MIXEDMAP;
 
if (use_ptemod)
vma->vm_flags |= VM_DONTCOPY;
-- 
2.8.0.rc2.1.gbe9624a