[dm-devel] [PATCH v3 13/14] filesystem-dax: gate calls to dax_flush() on QUEUE_FLAG_WC

Dan Williams dan.j.williams at intel.com
Fri Jun 9 20:24:56 UTC 2017


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

diff --git a/fs/dax.c b/fs/dax.c
index 6d8699feae2e..c3140343ff7e 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -783,7 +783,8 @@ 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
@@ -975,7 +976,8 @@ 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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