linux-kernel - Re: [PATCH v4 13/14] libnvdimm, pmem: gate cache management on QUEUE_FLAG_WC in pmem_dax

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Message-ID: <20170615080911.GC1764@quack2.suse.cz>
Date:   Thu, 15 Jun 2017 10:09:11 +0200
From:   Jan Kara <jack@...e.cz>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     linux-nvdimm@...ts.01.org, Jan Kara <jack@...e.cz>,
        Matthew Wilcox <mawilcox@...rosoft.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Jeff Moyer <jmoyer@...hat.com>,
        linux-fsdevel@...r.kernel.org,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v4 13/14] libnvdimm, pmem: gate cache management on
 QUEUE_FLAG_WC in pmem_dax_flush()

On Wed 14-06-17 16:11:26, Dan Williams wrote:
> Some platforms arrange for cpu caches to be flushed on power-fail. On
> those platforms there is no requirement that the kernel track and flush
> potentially dirty cache lines. Given that we still insert entries into
> the radix for locking purposes this patch only disables the cache flush
> loop, not the dirty tracking.
> 
> Userspace can override the default cache setting via the block device
> queue "write_cache" attribute in sysfs.
> 
> Cc: Jeff Moyer <jmoyer@...hat.com>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Matthew Wilcox <mawilcox@...rosoft.com>
> Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>
> Suggested-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>

Looks good. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
> Changes since v3:
> * move the check of QUEUE_FLAG_WC into the pmem driver directly (Jan)
> 
>  drivers/nvdimm/pmem.c |   11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> index 06f6c27ec1e9..49938b246a7b 100644
> --- a/drivers/nvdimm/pmem.c
> +++ b/drivers/nvdimm/pmem.c
> @@ -244,7 +244,16 @@ static size_t pmem_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff,
>  static void pmem_dax_flush(struct dax_device *dax_dev, pgoff_t pgoff,
>  		void *addr, size_t size)
>  {
> -	arch_wb_cache_pmem(addr, size);
> +	struct pmem_device *pmem = dax_get_private(dax_dev);
> +	struct gendisk *disk = pmem->disk;
> +	struct request_queue *q = disk->queue;
> +
> +	/*
> +	 * Only perform cache management when the queue has caching
> +	 * enabled.
> +	 */
> +	if (test_bit(QUEUE_FLAG_WC, &q->queue_flags))
> +		arch_wb_cache_pmem(addr, size);
>  }
>  
>  static const struct dax_operations pmem_dax_ops = {
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR