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From: Christoph Hellwig <hch@infradead.org>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: linux-fsdevel@vger.kernel.org, linux-nvdimm@lists.01.org,
	hch@infradead.org, dm-devel@redhat.com
Subject: Re: [PATCH 1/5] dax, pmem: Add a dax operation zero_page_range
Date: Wed, 5 Feb 2020 10:30:50 -0800
Message-ID: <20200205183050.GA26711@infradead.org> (raw)
In-Reply-To: <20200203200029.4592-2-vgoyal@redhat.com>

> +	/*
> +	 * There are no users as of now. Once users are there, fix dm code
> +	 * to be able to split a long range across targets.
> +	 */

This comment confused me.  I think this wants to say something like:

	/*
	 * There are now callers that want to zero across a page boundary as of
	 * now.  Once there are users this check can be removed after the
	 * device mapper code has been updated to split ranges across targets.
	 */

> +static int pmem_dax_zero_page_range(struct dax_device *dax_dev, pgoff_t pgoff,
> +				    unsigned int offset, size_t len)
> +{
> +	int rc = 0;
> +	phys_addr_t phys_pos = pgoff * PAGE_SIZE + offset;

Any reason not to pass a phys_addr_t in the calling convention for the
method and maybe also for dax_zero_page_range itself?

> +	sector_start = ALIGN(phys_pos, 512)/512;
> +	sector_end = ALIGN_DOWN(phys_pos + bytes, 512)/512;

Missing whitespaces.  Also this could use DIV_ROUND_UP and
DIV_ROUND_DOWN.

> +	if (sector_end > sector_start)
> +		nr_sectors = sector_end - sector_start;
> +
> +	if (nr_sectors &&
> +	    unlikely(is_bad_pmem(&pmem->bb, sector_start,
> +				 nr_sectors * 512)))
> +		bad_pmem = true;

How could nr_sectors be zero?

> +	write_pmem(pmem_addr, page, 0, bytes);
> +	if (unlikely(bad_pmem)) {
> +		/*
> +		 * Pass block aligned offset and length. That seems
> +		 * to work as of now. Other finer grained alignment
> +		 * cases can be addressed later if need be.
> +		 */
> +		rc = pmem_clear_poison(pmem, ALIGN(pmem_off, 512),
> +				       nr_sectors * 512);
> +		write_pmem(pmem_addr, page, 0, bytes);
> +	}

This code largerly duplicates the write side of pmem_do_bvec.  I
think it might make sense to split pmem_do_bvec into a read and a write
side as a prep patch, and then reuse the write side here.

> +int generic_dax_zero_page_range(struct dax_device *dax_dev, pgoff_t pgoff,
> +				 unsigned int offset, size_t len);

This should probably go into a separare are of the header and have
comment about being a section for generic helpers for drivers.
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Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-03 20:00 [RFC PATCH 0/5][V2] dax,pmem: Provide a dax operation to zero range of memory Vivek Goyal
2020-02-03 20:00 ` [PATCH 1/5] dax, pmem: Add a dax operation zero_page_range Vivek Goyal
2020-02-05 18:30   ` Christoph Hellwig [this message]
2020-02-05 20:02     ` Vivek Goyal
2020-02-06  0:40       ` Dan Williams
2020-02-06  7:41         ` Christoph Hellwig
2020-02-07 16:57           ` Dan Williams
2020-02-07 17:01             ` Vivek Goyal
2020-02-07 17:06               ` Dan Williams
2020-02-06 14:34         ` Vivek Goyal
2020-02-07 16:58           ` Dan Williams
2020-02-03 20:00 ` [PATCH 2/5] s390,dax: Add dax zero_page_range operation to dcssblk driver Vivek Goyal
2020-02-05 18:32   ` Christoph Hellwig
2020-02-05 20:04     ` Vivek Goyal
2020-02-03 20:00 ` [PATCH 3/5] dm,dax: Add dax zero_page_range operation Vivek Goyal
2020-02-05 18:33   ` Christoph Hellwig
2020-02-07 16:34     ` Vivek Goyal
2020-02-03 20:00 ` [PATCH 4/5] dax,iomap: Start using dax native zero_page_range() Vivek Goyal
2020-02-05 18:33   ` Christoph Hellwig
2020-02-05 20:10     ` Vivek Goyal
2020-02-07 15:31     ` Vivek Goyal
2020-02-03 20:00 ` [PATCH 5/5] dax,iomap: Add helper dax_iomap_zero() to zero a range Vivek Goyal
2020-02-04  5:17   ` kbuild test robot
2020-02-05 18:36   ` Christoph Hellwig
2020-02-05 20:15     ` Vivek Goyal

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