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Commit c86d8db3 authored by Jan Kara's avatar Jan Kara Committed by Theodore Ts'o
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ext4: implement allocation of pre-zeroed blocks 



DAX page fault path needs to get blocks that are pre-zeroed to avoid
races when two concurrent page faults happen in the same block of a
file. Implement support for this in ext4_map_blocks().

Signed-off-by: default avatarJan Kara <jack@suse.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 53085fac

fs/ext4/ext4.h

+4 −0
Original line number Diff line number Diff line
@@ -557,6 +557,10 @@ enum { 
#define EXT4_GET_BLOCKS_KEEP_SIZE		0x0080

	/* Convert written extents to unwritten */

#define EXT4_GET_BLOCKS_CONVERT_UNWRITTEN	0x0100

	/* Write zeros to newly created written extents */

#define EXT4_GET_BLOCKS_ZERO			0x0200

#define EXT4_GET_BLOCKS_CREATE_ZERO		(EXT4_GET_BLOCKS_CREATE |\

					EXT4_GET_BLOCKS_ZERO)



/*

 * The bit position of these flags must not overlap with any of the

fs/ext4/extents.c

+8 −0
Original line number Diff line number Diff line
@@ -4044,6 +4044,14 @@ ext4_ext_handle_unwritten_extents(handle_t *handle, struct inode *inode, 
	}

	/* IO end_io complete, convert the filled extent to written */

	if (flags & EXT4_GET_BLOCKS_CONVERT) {

		if (flags & EXT4_GET_BLOCKS_ZERO) {

			if (allocated > map->m_len)

				allocated = map->m_len;

			err = ext4_issue_zeroout(inode, map->m_lblk, newblock,

						 allocated);

			if (err < 0)

				goto out2;

		}

		ret = ext4_convert_unwritten_extents_endio(handle, inode, map,

							   ppath);

		if (ret >= 0) {

fs/ext4/inode.c

+22 −3
Original line number Diff line number Diff line
@@ -636,6 +636,22 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode, 
			WARN_ON(1);

		}



		/*

		 * We have to zeroout blocks before inserting them into extent

		 * status tree. Otherwise someone could look them up there and

		 * use them before they are really zeroed.

		 */

		if (flags & EXT4_GET_BLOCKS_ZERO &&

		    map->m_flags & EXT4_MAP_MAPPED &&

		    map->m_flags & EXT4_MAP_NEW) {

			ret = ext4_issue_zeroout(inode, map->m_lblk,

						 map->m_pblk, map->m_len);

			if (ret) {

				retval = ret;

				goto out_sem;

			}

		}



		/*

		 * If the extent has been zeroed out, we don't need to update

		 * extent status tree.
@@ -643,7 +659,7 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode, 
		if ((flags & EXT4_GET_BLOCKS_PRE_IO) &&

		    ext4_es_lookup_extent(inode, map->m_lblk, &es)) {

			if (ext4_es_is_written(&es))

				goto has_zeroout;

				goto out_sem;

		}

		status = map->m_flags & EXT4_MAP_UNWRITTEN ?

				EXTENT_STATUS_UNWRITTEN : EXTENT_STATUS_WRITTEN;
@@ -654,11 +670,13 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode, 
			status |= EXTENT_STATUS_DELAYED;

		ret = ext4_es_insert_extent(inode, map->m_lblk, map->m_len,

					    map->m_pblk, status);

		if (ret < 0)

		if (ret < 0) {

			retval = ret;

			goto out_sem;

		}

	}



has_zeroout:

out_sem:

	up_write((&EXT4_I(inode)->i_data_sem));

	if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) {

		ret = check_block_validity(inode, map);
@@ -3083,6 +3101,7 @@ int ext4_get_block_dax(struct inode *inode, sector_t iblock, 
		   struct buffer_head *bh_result, int create)

{

	int flags = EXT4_GET_BLOCKS_PRE_IO | EXT4_GET_BLOCKS_UNWRIT_EXT;



	if (create)

		flags |= EXT4_GET_BLOCKS_CREATE;

	ext4_debug("ext4_get_block_dax: inode %lu, create flag %d\n",

include/trace/events/ext4.h

+2 −1
Original line number Diff line number Diff line
@@ -42,7 +42,8 @@ struct extent_status; 
	{ EXT4_GET_BLOCKS_CONVERT,		"CONVERT" },		\

	{ EXT4_GET_BLOCKS_METADATA_NOFAIL,	"METADATA_NOFAIL" },	\

	{ EXT4_GET_BLOCKS_NO_NORMALIZE,		"NO_NORMALIZE" },	\

	{ EXT4_GET_BLOCKS_KEEP_SIZE,		"KEEP_SIZE" })

	{ EXT4_GET_BLOCKS_KEEP_SIZE,		"KEEP_SIZE" },		\

	{ EXT4_GET_BLOCKS_ZERO,			"ZERO" })



#define show_mflags(flags) __print_flags(flags, "",	\

	{ EXT4_MAP_NEW,		"N" },			\