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 21:03:19 +0000
From:	"Verma, Vishal L" <vishal.l.verma@...el.com>
To:	"Williams, Dan J" <dan.j.williams@...el.com>
CC:	"linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
	"xfs@....sgi.com" <xfs@....sgi.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"axboe@...com" <axboe@...com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"ross.zwisler@...ux.intel.com" <ross.zwisler@...ux.intel.com>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>,
	"david@...morbit.com" <david@...morbit.com>,
	"jack@...e.cz" <jack@...e.cz>
Subject: Re: [PATCH 4/5] dax: use sb_issue_zerout instead of calling
 dax_clear_sectors

On Fri, 2016-03-25 at 11:47 -0700, Dan Williams wrote:
> On Thu, Mar 24, 2016 at 4:17 PM, Vishal Verma <vishal.l.verma@...el.c
> om> 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?

Could you point me to where these might be? I thought once we've
converted all the zeroout type callers (by removing dax_clear_sectors),
and fixed up dax_do_io to try a driver fallback, we've handled all the
media error cases in dax..