Commit e37c9e17 authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle) Committed by Theodore Ts'o
Browse files

ext4: reduce stack usage in ext4_mpage_readpages() 



This function is very similar to do_mpage_readpage() and a similar
approach to that taken in commit 12ac5a65 will work.  As in
do_mpage_readpage(), we only use this array for checking block contiguity
and we can do that more efficiently with a little arithmetic.

Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Link: https://patch.msgid.link/20240718223005.568869-1-willy@infradead.org


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent f5cacdc6

fs/ext4/readpage.c

+8 −8
Original line number Diff line number Diff line
@@ -221,7 +221,7 @@ int ext4_mpage_readpages(struct inode *inode, 
	sector_t block_in_file;

	sector_t last_block;

	sector_t last_block_in_file;

	sector_t blocks[MAX_BUF_PER_PAGE];

	sector_t first_block;

	unsigned page_block;

	struct block_device *bdev = inode->i_sb->s_bdev;

	int length;
@@ -263,6 +263,7 @@ int ext4_mpage_readpages(struct inode *inode, 
			unsigned map_offset = block_in_file - map.m_lblk;

			unsigned last = map.m_len - map_offset;



			first_block = map.m_pblk + map_offset;

			for (relative_block = 0; ; relative_block++) {

				if (relative_block == last) {

					/* needed? */
@@ -271,8 +272,6 @@ int ext4_mpage_readpages(struct inode *inode, 
				}

				if (page_block == blocks_per_page)

					break;

				blocks[page_block] = map.m_pblk + map_offset +

					relative_block;

				page_block++;

				block_in_file++;

			}
@@ -307,7 +306,9 @@ int ext4_mpage_readpages(struct inode *inode, 
				goto confused;		/* hole -> non-hole */



			/* Contiguous blocks? */

			if (page_block && blocks[page_block-1] != map.m_pblk-1)

			if (!page_block)

				first_block = map.m_pblk;

			else if (first_block + page_block != map.m_pblk)

				goto confused;

			for (relative_block = 0; ; relative_block++) {

				if (relative_block == map.m_len) {
@@ -316,7 +317,6 @@ int ext4_mpage_readpages(struct inode *inode, 
					break;

				} else if (page_block == blocks_per_page)

					break;

				blocks[page_block] = map.m_pblk+relative_block;

				page_block++;

				block_in_file++;

			}
@@ -339,7 +339,7 @@ int ext4_mpage_readpages(struct inode *inode, 
		 * This folio will go to BIO.  Do we need to send this

		 * BIO off first?

		 */

		if (bio && (last_block_in_bio != blocks[0] - 1 ||

		if (bio && (last_block_in_bio != first_block - 1 ||

			    !fscrypt_mergeable_bio(bio, inode, next_block))) {

		submit_and_realloc:

			submit_bio(bio);
@@ -355,7 +355,7 @@ int ext4_mpage_readpages(struct inode *inode, 
			fscrypt_set_bio_crypt_ctx(bio, inode, next_block,

						  GFP_KERNEL);

			ext4_set_bio_post_read_ctx(bio, inode, folio->index);

			bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);

			bio->bi_iter.bi_sector = first_block << (blkbits - 9);

			bio->bi_end_io = mpage_end_io;

			if (rac)

				bio->bi_opf |= REQ_RAHEAD;
@@ -371,7 +371,7 @@ int ext4_mpage_readpages(struct inode *inode, 
			submit_bio(bio);

			bio = NULL;

		} else

			last_block_in_bio = blocks[blocks_per_page - 1];

			last_block_in_bio = first_block + blocks_per_page - 1;

		continue;

	confused:

		if (bio) {