The patch titled
Subject: mm: silently skip readahead for DAX inodes
has been added to the -mm tree. Its filename is
mm-silently-skip-readahead-for-dax-inodes.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-silently-skip-readahead-for-dax-inodes.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-silently-skip-readahead-for-dax-inodes.patch
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------------------------------------------------------
From: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Subject: mm: silently skip readahead for DAX inodes
For DAX inodes we need to be careful to never have page cache pages in the
mapping->page_tree. This radix tree should be composed only of DAX
exceptional entries and zero pages.
ltp's readahead02 test was triggering a warning because we were trying to
insert a DAX exceptional entry but found that a page cache page had
already been inserted into the tree. This page was being inserted into
the radix tree in response to a readahead(2) call.
Readahead doesn't make sense for DAX inodes, but we don't want it to report
a failure either. Instead, we just return success and don't do any work.
Link: http://lkml.kernel.org/r/20160824221429.21158-1-ross.zwisler@xxxxxxxxxxxxxxx
Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Reported-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.5+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/readahead.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff -puN mm/readahead.c~mm-silently-skip-readahead-for-dax-inodes mm/readahead.c
--- a/mm/readahead.c~mm-silently-skip-readahead-for-dax-inodes
+++ a/mm/readahead.c
@@ -8,6 +8,7 @@
*/
#include <linux/kernel.h>
+#include <linux/dax.h>
#include <linux/gfp.h>
#include <linux/export.h>
#include <linux/blkdev.h>
@@ -544,6 +545,14 @@ do_readahead(struct address_space *mappi
if (!mapping || !mapping->a_ops)
return -EINVAL;
+ /*
+ * Readahead doesn't make sense for DAX inodes, but we don't want it
+ * to report a failure either. Instead, we just return success and
+ * don't do any work.
+ */
+ if (dax_mapping(mapping))
+ return 0;
+
return force_page_cache_readahead(mapping, filp, index, nr);
}
_
Patches currently in -mm which might be from ross.zwisler@xxxxxxxxxxxxxxx are
mm-silently-skip-readahead-for-dax-inodes.patch
radix-tree-slot-can-be-null-in-radix_tree_next_slot.patch
radix-tree-tests-add-iteration-test.patch
radix-tree-tests-properly-initialize-mutex.patch
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