linux-ext4 - Re: [PATCH 4/5] dax: use sb_issue_zerout instead of calling dax_clear

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Date:	Fri, 25 Mar 2016 11:47:26 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Vishal Verma <vishal.l.verma@...el.com>
Cc:	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-block@...r.kernel.org, XFS Developers <xfs@....sgi.com>,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	Linux MM <linux-mm@...ck.org>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>,
	Jens Axboe <axboe@...com>, Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 4/5] dax: use sb_issue_zerout instead of calling dax_clear_sectors

On Thu, Mar 24, 2016 at 4:17 PM, Vishal Verma <vishal.l.verma@...el.com> wrote:
> From: Matthew Wilcox <matthew.r.wilcox@...el.com>
>
> dax_clear_sectors() cannot handle poisoned blocks.  These must be
> zeroed using the BIO interface instead.  Convert ext2 and XFS to use
> only sb_issue_zerout().
>
> Signed-off-by: Matthew Wilcox <matthew.r.wilcox@...el.com>
> [vishal: Also remove the dax_clear_sectors function entirely]
> Signed-off-by: Vishal Verma <vishal.l.verma@...el.com>
> ---
>  fs/dax.c               | 32 --------------------------------
>  fs/ext2/inode.c        |  7 +++----
>  fs/xfs/xfs_bmap_util.c |  9 ---------
>  include/linux/dax.h    |  1 -
>  4 files changed, 3 insertions(+), 46 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index bb7e9f8..a30481e 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -78,38 +78,6 @@ struct page *read_dax_sector(struct block_device *bdev, sector_t n)
>         return page;
>  }
>
> -/*
> - * dax_clear_sectors() is called from within transaction context from XFS,
> - * and hence this means the stack from this point must follow GFP_NOFS
> - * semantics for all operations.
> - */
> -int dax_clear_sectors(struct block_device *bdev, sector_t _sector, long _size)
> -{
> -       struct blk_dax_ctl dax = {
> -               .sector = _sector,
> -               .size = _size,
> -       };
> -
> -       might_sleep();
> -       do {
> -               long count, sz;
> -
> -               count = dax_map_atomic(bdev, &dax);
> -               if (count < 0)
> -                       return count;
> -               sz = min_t(long, count, SZ_128K);
> -               clear_pmem(dax.addr, sz);
> -               dax.size -= sz;
> -               dax.sector += sz / 512;
> -               dax_unmap_atomic(bdev, &dax);
> -               cond_resched();
> -       } while (dax.size);
> -
> -       wmb_pmem();
> -       return 0;
> -}
> -EXPORT_SYMBOL_GPL(dax_clear_sectors);

What about the other unwritten extent conversions in the dax path?
Shouldn't those be converted to block-layer zero-outs as well?
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