| Message ID | 20151022171044.38343.2553.stgit@dwillia2-desk3.amr.corp.intel.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
Dan Williams <dan.j.williams@intel.com> writes: > If an application wants exclusive access to all of the persistent memory > provided by an NVDIMM namespace it can use this raw-block-dax facility > to forgo establishing a filesystem. This capability is targeted > primarily to hypervisors wanting to provision persistent memory for > guests. OK, I'm going to expose my ignorance here. :) Why does the block device need a page_mkwrite handler? -Jeff > Cc: Jeff Moyer <jmoyer@redhat.com> > Cc: Christoph Hellwig <hch@lst.de> > Cc: Dave Chinner <david@fromorbit.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Ross Zwisler <ross.zwisler@linux.intel.com> > Reviewed-by: Jan Kara <jack@suse.com> > Signed-off-by: Dan Williams <dan.j.williams@intel.com> > --- > fs/block_dev.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 59 insertions(+), 1 deletion(-) > > diff --git a/fs/block_dev.c b/fs/block_dev.c > index c1f691859a56..210d05103657 100644 > --- a/fs/block_dev.c > +++ b/fs/block_dev.c > @@ -1687,13 +1687,71 @@ static const struct address_space_operations def_blk_aops = { > .is_dirty_writeback = buffer_check_dirty_writeback, > }; > > +#ifdef CONFIG_FS_DAX > +/* > + * In the raw block case we do not need to contend with truncation nor > + * unwritten file extents. Without those concerns there is no need for > + * additional locking beyond the mmap_sem context that these routines > + * are already executing under. > + * > + * Note, there is no protection if the block device is dynamically > + * resized (partition grow/shrink) during a fault. A stable block device > + * size is already not enforced in the blkdev_direct_IO path. > + * > + * For DAX, it is the responsibility of the block device driver to > + * ensure the whole-disk device size is stable while requests are in > + * flight. > + * > + * Finally, in contrast to the generic_file_mmap() path, there are no > + * calls to sb_start_pagefault(). That is meant to synchronize write > + * faults against requests to freeze the contents of the filesystem > + * hosting vma->vm_file. However, in the case of a block device special > + * file, it is a 0-sized device node usually hosted on devtmpfs, i.e. > + * nothing to do with the super_block for bdev_file_inode(vma->vm_file). > + * We could call get_super() in this path to retrieve the right > + * super_block, but the generic_file_mmap() path does not do this for > + * the CONFIG_FS_DAX=n case. > + */ > +static int blkdev_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf) > +{ > + return __dax_fault(vma, vmf, blkdev_get_block, NULL); > +} > + > +static int blkdev_dax_pmd_fault(struct vm_area_struct *vma, unsigned long addr, > + pmd_t *pmd, unsigned int flags) > +{ > + return __dax_pmd_fault(vma, addr, pmd, flags, blkdev_get_block, NULL); > +} > + > +static const struct vm_operations_struct blkdev_dax_vm_ops = { > + .page_mkwrite = blkdev_dax_fault, > + .fault = blkdev_dax_fault, > + .pmd_fault = blkdev_dax_pmd_fault, > +}; > + > +static int blkdev_mmap(struct file *file, struct vm_area_struct *vma) > +{ > + struct inode *bd_inode = bdev_file_inode(file); > + > + if (!IS_DAX(bd_inode)) > + return generic_file_mmap(file, vma); > + > + file_accessed(file); > + vma->vm_ops = &blkdev_dax_vm_ops; > + vma->vm_flags |= VM_MIXEDMAP | VM_HUGEPAGE; > + return 0; > +} > +#else > +#define blkdev_mmap generic_file_mmap > +#endif > + > const struct file_operations def_blk_fops = { > .open = blkdev_open, > .release = blkdev_close, > .llseek = block_llseek, > .read_iter = blkdev_read_iter, > .write_iter = blkdev_write_iter, > - .mmap = generic_file_mmap, > + .mmap = blkdev_mmap, > .fsync = blkdev_fsync, > .unlocked_ioctl = block_ioctl, > #ifdef CONFIG_COMPAT
On Thu, Oct 29, 2015 at 5:50 AM, Jeff Moyer <jmoyer@redhat.com> wrote: > Dan Williams <dan.j.williams@intel.com> writes: > >> If an application wants exclusive access to all of the persistent memory >> provided by an NVDIMM namespace it can use this raw-block-dax facility >> to forgo establishing a filesystem. This capability is targeted >> primarily to hypervisors wanting to provision persistent memory for >> guests. > > OK, I'm going to expose my ignorance here. :) Why does the block device > need a page_mkwrite handler? > You're right, it buys us nothing, and deleting it saves having to comment on why this page_mkwrite instance is not calling sb_start_pagefault.
diff --git a/fs/block_dev.c b/fs/block_dev.c index c1f691859a56..210d05103657 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -1687,13 +1687,71 @@ static const struct address_space_operations def_blk_aops = { .is_dirty_writeback = buffer_check_dirty_writeback, }; +#ifdef CONFIG_FS_DAX +/* + * In the raw block case we do not need to contend with truncation nor + * unwritten file extents. Without those concerns there is no need for + * additional locking beyond the mmap_sem context that these routines + * are already executing under. + * + * Note, there is no protection if the block device is dynamically + * resized (partition grow/shrink) during a fault. A stable block device + * size is already not enforced in the blkdev_direct_IO path. + * + * For DAX, it is the responsibility of the block device driver to + * ensure the whole-disk device size is stable while requests are in + * flight. + * + * Finally, in contrast to the generic_file_mmap() path, there are no + * calls to sb_start_pagefault(). That is meant to synchronize write + * faults against requests to freeze the contents of the filesystem + * hosting vma->vm_file. However, in the case of a block device special + * file, it is a 0-sized device node usually hosted on devtmpfs, i.e. + * nothing to do with the super_block for bdev_file_inode(vma->vm_file). + * We could call get_super() in this path to retrieve the right + * super_block, but the generic_file_mmap() path does not do this for + * the CONFIG_FS_DAX=n case. + */ +static int blkdev_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf) +{ + return __dax_fault(vma, vmf, blkdev_get_block, NULL); +} + +static int blkdev_dax_pmd_fault(struct vm_area_struct *vma, unsigned long addr, + pmd_t *pmd, unsigned int flags) +{ + return __dax_pmd_fault(vma, addr, pmd, flags, blkdev_get_block, NULL); +} + +static const struct vm_operations_struct blkdev_dax_vm_ops = { + .page_mkwrite = blkdev_dax_fault, + .fault = blkdev_dax_fault, + .pmd_fault = blkdev_dax_pmd_fault, +}; + +static int blkdev_mmap(struct file *file, struct vm_area_struct *vma) +{ + struct inode *bd_inode = bdev_file_inode(file); + + if (!IS_DAX(bd_inode)) + return generic_file_mmap(file, vma); + + file_accessed(file); + vma->vm_ops = &blkdev_dax_vm_ops; + vma->vm_flags |= VM_MIXEDMAP | VM_HUGEPAGE; + return 0; +} +#else +#define blkdev_mmap generic_file_mmap +#endif + const struct file_operations def_blk_fops = { .open = blkdev_open, .release = blkdev_close, .llseek = block_llseek, .read_iter = blkdev_read_iter, .write_iter = blkdev_write_iter, - .mmap = generic_file_mmap, + .mmap = blkdev_mmap, .fsync = blkdev_fsync, .unlocked_ioctl = block_ioctl, #ifdef CONFIG_COMPAT