Re: [RFC][PATCH] dax: Do not try to clear poison for partial pages

[Christoph Hellwig <hch@infradead.org>]

On Wed, Jan 29, 2020 at 04:03:37PM -0500, Vivek Goyal wrote:
> I am looking into getting rid of dependency on block device in dax
> path. One such place is __dax_zero_page_range() which checks if
> range being zeroed is aligned to block device logical size, then
> it calls bdev_issue_zeroout() instead of doing memset(). Calling
> blkdev_issue_zeroout() also clears bad blocks and poison if any
> in that range.
> 
> This path is used by iomap_zero_range() which in-turn is being
> used by filesystems to zero partial filesystem system blocks.
> For zeroing full filesystem blocks we seem to be calling
> blkdev_issue_zeroout() which clears bad blocks and poison in that
> range.
> 
> So this code currently only seems to help with partial filesystem
> block zeroing. That too only if truncation/hole_punch happens on
> device logical block size boundary.
> 
> To avoid using blkdev_issue_zeroout() in this path, I proposed another
> patch here which adds another dax operation to zero out a rangex and
> clear poison.

I'll have to defer to Dan and other on the poison clearing issue,
as it keeps confusing me everytime I look into how it is supposed
to work..  But in the end we'll need a path that doesn't realy on
the block device to clear poison anyway, so I think a method will
ultimatively be needed.  That being said this patch looks nice :)