Messages in this thread Patch in this message | | | From | Boris Ostrovsky <> | Subject | [PATCH v2] xen/gntdev: Use mempolicy instead of VM_IO flag to avoid NUMA balancing | Date | Wed, 16 Nov 2016 12:46:18 -0500 |
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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, instead of setting VM_IO use mempolicy that prohibits page migration (i.e. clear policy's MPOL_F_MOF|MPOL_F_MORON)
Reported-by: Olaf Hering <olaf@aepfle.de> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> Reviewed-by: David Vrabel <david.vrabel@citrix.com> --- Changes in v2: * Corrected the commit message
Unfortunately I haven't been able to trigger NUMA balancing so while I tested this in general I am not sure I actually exercised the code path.
drivers/xen/gntdev.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c index bb95212..743e6f0 100644 --- a/drivers/xen/gntdev.c +++ b/drivers/xen/gntdev.c @@ -35,6 +35,7 @@ #include <linux/spinlock.h> #include <linux/slab.h> #include <linux/highmem.h> +#include <linux/mempolicy.h> #include <xen/xen.h> #include <xen/grant_table.h> @@ -1007,8 +1008,20 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma) vma->vm_ops = &gntdev_vmops; - vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_IO; + vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP; +#ifdef CONFIG_NUMA + /* Prevent NUMA balancing */ + if (vma->vm_policy) + vma->vm_policy->flags &= ~(MPOL_F_MOF | MPOL_F_MORON); + else { + struct mempolicy *pol = get_task_policy(current); + + vma->vm_policy = mpol_dup(pol); + if (vma->vm_policy) + vma->vm_policy->flags &= ~(MPOL_F_MOF | MPOL_F_MORON); + } +#endif if (use_ptemod) vma->vm_flags |= VM_DONTCOPY; -- 2.5.5
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