dax: Allow DAX code to replace exceptional entries (4f622938) · Commits · 戴 / test

Currently we forbid page_cache_tree_insert() to replace exceptional radix tree entries for DAX inodes. However to make DAX faults race free we will lock radix tree entries and when hole is created, we need to replace such locked radix tree entry with a hole page. So modify page_cache_tree_insert() to allow that. Reviewed-by:

Ross Zwisler <ross.zwisler@linux.intel.com> Signed-off-by:

Jan Kara <jack@suse.cz> Signed-off-by:

Ross Zwisler <ross.zwisler@linux.intel.com>

include/linux/dax.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -3,6 +3,7 @@

		#include <linux/fs.h>
		#include <linux/mm.h>
		#include <linux/radix-tree.h>
		#include <asm/pgtable.h>

		/* We use lowest available exceptional entry bit for locking */

mm/filemap.c

+14 −7

Original line number	Diff line number	Diff line
		@@ -597,14 +597,21 @@ static int page_cache_tree_insert(struct address_space *mapping,
		if (!radix_tree_exceptional_entry(p))
		return -EEXIST;

		if (WARN_ON(dax_mapping(mapping)))
		return -EINVAL;

		mapping->nrexceptional--;
		if (!dax_mapping(mapping)) {
		if (shadowp)
		*shadowp = p;
		mapping->nrexceptional--;
		if (node)
		workingset_node_shadows_dec(node);
		} else {
		/* DAX can replace empty locked entry with a hole */
		WARN_ON_ONCE(p !=
		(void *)(RADIX_TREE_EXCEPTIONAL_ENTRY \|
		RADIX_DAX_ENTRY_LOCK));
		/* DAX accounts exceptional entries as normal pages */
		if (node)
		workingset_node_pages_dec(node);
		}
		}
		radix_tree_replace_slot(slot, page);
		mapping->nrpages++;

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