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[PATCH v2 32/33] filesystem-dax: gate calls to dax_flush() on QUEUE_FLAG_WC

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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: Jan Kara <jack@suse.cz>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 fs/dax.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index f37ed21e4093..5b7ee1bc74d0 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -797,7 +797,8 @@ static int dax_writeback_one(struct block_device *bdev,
 	}
 
 	dax_mapping_entry_mkclean(mapping, index, pfn_t_to_pfn(pfn));
-	dax_flush(dax_dev, pgoff, kaddr, size);
+	if (test_bit(QUEUE_FLAG_WC, &bdev->bd_queue->queue_flags))
+		dax_flush(dax_dev, pgoff, kaddr, size);
 	/*
 	 * After we have flushed the cache, we can clear the dirty tag. There
 	 * cannot be new dirty data in the pfn after the flush has completed as
@@ -982,7 +983,8 @@ int __dax_zero_page_range(struct block_device *bdev,
 			return rc;
 		}
 		memset(kaddr + offset, 0, size);
-		dax_flush(dax_dev, pgoff, kaddr + offset, size);
+		if (test_bit(QUEUE_FLAG_WC, &bdev->bd_queue->queue_flags))
+			dax_flush(dax_dev, pgoff, kaddr + offset, size);
 		dax_read_unlock(id);
 	}
 	return 0;

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[PATCH v2 00/33] dax: introduce dax_operations Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:40 +0200
  [PATCH v2 11/33] dm: add dax_device and dax_operations support Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
    Re: [PATCH v2 11/33] dm: add dax_device and dax_operations support Dan Williams <dan.j.williams@intel.com> - 2017-04-15 17:20 +0200
  [PATCH v2 26/33] x86, dax,  libnvdimm: move wb_cache_pmem() to libnvdimm Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 13/33] ext2, ext4,  xfs: retrieve dax_device for iomap operations Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 32/33] filesystem-dax: gate calls to dax_flush() on  QUEUE_FLAG_WC Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 22/33] dax,  pmem: introduce an optional 'flush' dax_operation Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 20/33] dm: add ->copy_from_iter() dax operation support Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 21/33] filesystem-dax: convert to dax_copy_from_iter() Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 24/33] filesystem-dax: convert to dax_flush() Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 30/33] libnvdimm, pmem: fix persistence warning Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 23/33] dm: add ->flush() dax operation support Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 15/33] filesystem-dax: convert to dax_direct_access() Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 18/33] x86, dax,  pmem: remove indirection around memcpy_from_pmem() Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 29/33] uio, libnvdimm,  pmem: implement cache bypass for all copy_from_iter() operations Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
    Re: [PATCH v2 29/33] uio, libnvdimm, pmem: implement cache bypass  for all copy_from_iter() operations Jan Kara <jack@suse.cz> - 2017-04-24 17:10 +0200
  [PATCH v2 10/33] dax: introduce dax_direct_access() Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 28/33] x86, libnvdimm,  dax: stop abusing __copy_user_nocache Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 25/33] x86,  dax: replace clear_pmem() with open coded memset + dax_ops->flush Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 14/33] Revert "block: use DAX for partition table reads" Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 27/33] x86, libnvdimm,  pmem: move arch_invalidate_pmem() to libnvdimm Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 17/33] block: remove block_device_operations  ->direct_access() Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 33/33] libnvdimm,  pmem: disable dax flushing when pmem is fronting a volatile region Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 16/33] block,  dax: convert bdev_dax_supported() to dax_direct_access() Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 19/33] dax, pmem: introduce 'copy_from_iter' dax operation Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 12/33] dm: teach dm-targets to use a dax_device +  dax_operations Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 31/33] libnvdimm, nfit: enable support for volatile ranges Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200
  [PATCH v2 02/33] dax: refactor dax-fs into a generic provider of  'struct dax_device' instances Dan Williams <dan.j.williams@intel.com> - 2017-04-15 04:50 +0200

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