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Message-ID: <20160122150129.GL16898@quack.suse.cz>
Date: Fri, 22 Jan 2016 16:01:29 +0100
From: Jan Kara <jack@...e.cz>
To: Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org,
Alexander Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
Dan Williams <dan.j.williams@...el.com>,
Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.com>,
Matthew Wilcox <willy@...ux.intel.com>,
linux-fsdevel@...r.kernel.org, linux-nvdimm@...ts.01.org
Subject: Re: [PATCH v2 3/5] dax: improve documentation for fsync/msync
On Thu 21-01-16 10:46:02, Ross Zwisler wrote:
> Several of the subtleties and assumptions of the DAX fsync/msync
> implementation are not immediately obvious, so document them with comments.
>
> Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> Reported-by: Jan Kara <jack@...e.cz>
Thanks, the comments really help! Just two nits below, otherwise feel free
to add:
Reviewed-by: Jan Kara <jack@...e.cz>
> ---
> fs/dax.c | 30 ++++++++++++++++++++++++++++++
> 1 file changed, 30 insertions(+)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index d589113..55ae394 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -350,6 +350,13 @@ static int dax_radix_entry(struct address_space *mapping, pgoff_t index,
>
> if (!pmd_entry || type == RADIX_DAX_PMD)
> goto dirty;
> +
> + /*
> + * We only insert dirty PMD entries into the radix tree. This
> + * means we don't need to worry about removing a dirty PTE
> + * entry and inserting a clean PMD entry, thus reducing the
> + * range we would flush with a follow-up fsync/msync call.
> + */
May be acompany this with:
WARN_ON(pmd_entry && !dirty);
somewhere in dax_radix_entry()?
> radix_tree_delete(&mapping->page_tree, index);
> mapping->nrexceptional--;
> }
> @@ -912,6 +919,21 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
> }
> dax_unmap_atomic(bdev, &dax);
>
> + /*
> + * For PTE faults we insert a radix tree entry for reads, and
> + * leave it clean. Then on the first write we dirty the radix
> + * tree entry via the dax_pnf_mkwrite() path. This sequence
^^^ pfn
Honza
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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