Re: [RFC] nvfs: a filesystem for persistent memory

[Ritesh Harjani]

On 9/15/20 6:30 PM, Matthew Wilcox wrote:
> On Tue, Sep 15, 2020 at 08:34:41AM -0400, Mikulas Patocka wrote:
> > - when the fsck.nvfs tool mmaps the device /dev/pmem0, the kernel uses
> > buffer cache for the mapping. The buffer cache slows does fsck by a factor
> > of 5 to 10. Could it be possible to change the kernel so that it maps DAX
> > based block devices directly?
>
> Oh, because fs/block_dev.c has:
>          .mmap           = generic_file_mmap,
>
> I don't see why we shouldn't have a blkdev_mmap modelled after
> ext2_file_mmap() with the corresponding blkdev_dax_vm_ops.

pls help with below 2 queries:-

1. Can't we use ->direct_IO here to avoid the mentioned performance problem?
2. Any other existing use case where having this blkdev_dax_vm_ops be 
useful?

-ritesh