Commit df981d03 authored by Theodore Ts'o's avatar Theodore Ts'o
Browse files

ext4: add max_dir_size_kb mount option 



Very large directories can cause significant performance problems, or
perhaps even invoke the OOM killer, if the process is running in a
highly constrained memory environment (whether it is VM's with a small
amount of memory or in a small memory cgroup).

So it is useful, in cloud server/data center environments, to be able
to set a filesystem-wide cap on the maximum size of a directory, to
ensure that directories never get larger than a sane size.  We do this
via a new mount option, max_dir_size_kb.  If there is an attempt to
grow the directory larger than max_dir_size_kb, the system call will
return ENOSPC instead.

Google-Bug-Id: 6863013

Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent 01fc48e8

Documentation/filesystems/ext4.txt

+10 −0
Original line number Diff line number Diff line
@@ -375,6 +375,16 @@ dioread_nolock locking. If the dioread_nolock option is specified 
			Because of the restrictions this options comprises

			it is off by default (e.g. dioread_lock).



max_dir_size_kb=n	This limits the size of directories so that any

			attempt to expand them beyond the specified

			limit in kilobytes will cause an ENOSPC error.

			This is useful in memory constrained

			environments, where a very large directory can

			cause severe performance problems or even

			provoke the Out Of Memory killer.  (For example,

			if there is only 512mb memory available, a 176mb

			directory may seriously cramp the system's style.)



i_version		Enable 64-bit inode version support. This option is

			off by default.

fs/ext4/ext4.h

+1 −0
Original line number Diff line number Diff line
@@ -1243,6 +1243,7 @@ struct ext4_sb_info { 
	unsigned int s_mb_order2_reqs;

	unsigned int s_mb_group_prealloc;

	unsigned int s_max_writeback_mb_bump;

	unsigned int s_max_dir_size_kb;

	/* where last allocation was done - for stream allocation */

	unsigned long s_mb_last_group;

	unsigned long s_mb_last_start;

fs/ext4/namei.c

+7 −0
Original line number Diff line number Diff line
@@ -55,6 +55,13 @@ static struct buffer_head *ext4_append(handle_t *handle, 
{

	struct buffer_head *bh;



	if (unlikely(EXT4_SB(inode->i_sb)->s_max_dir_size_kb &&

		     ((inode->i_size >> 10) >=

		      EXT4_SB(inode->i_sb)->s_max_dir_size_kb))) {

		*err = -ENOSPC;

		return NULL;

	}



	*block = inode->i_size >> inode->i_sb->s_blocksize_bits;



	bh = ext4_bread(handle, inode, *block, 1, err);

fs/ext4/super.c

+7 −0
Original line number Diff line number Diff line
@@ -1230,6 +1230,7 @@ enum { 
	Opt_inode_readahead_blks, Opt_journal_ioprio,

	Opt_dioread_nolock, Opt_dioread_lock,

	Opt_discard, Opt_nodiscard, Opt_init_itable, Opt_noinit_itable,

	Opt_max_dir_size_kb,

};



static const match_table_t tokens = {
@@ -1303,6 +1304,7 @@ static const match_table_t tokens = { 
	{Opt_init_itable, "init_itable=%u"},

	{Opt_init_itable, "init_itable"},

	{Opt_noinit_itable, "noinit_itable"},

	{Opt_max_dir_size_kb, "max_dir_size_kb=%u"},

	{Opt_removed, "check=none"},	/* mount option from ext2/3 */

	{Opt_removed, "nocheck"},	/* mount option from ext2/3 */

	{Opt_removed, "reservation"},	/* mount option from ext2/3 */
@@ -1483,6 +1485,7 @@ static const struct mount_opts { 
	{Opt_jqfmt_vfsold, QFMT_VFS_OLD, MOPT_QFMT},

	{Opt_jqfmt_vfsv0, QFMT_VFS_V0, MOPT_QFMT},

	{Opt_jqfmt_vfsv1, QFMT_VFS_V1, MOPT_QFMT},

	{Opt_max_dir_size_kb, 0, MOPT_GTE0},

	{Opt_err, 0, 0}

};
@@ -1598,6 +1601,8 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token, 
			if (!args->from)

				arg = EXT4_DEF_LI_WAIT_MULT;

			sbi->s_li_wait_mult = arg;

		} else if (token == Opt_max_dir_size_kb) {

			sbi->s_max_dir_size_kb = arg;

		} else if (token == Opt_stripe) {

			sbi->s_stripe = arg;

		} else if (m->flags & MOPT_DATAJ) {
@@ -1829,6 +1834,8 @@ static int _ext4_show_options(struct seq_file *seq, struct super_block *sb, 
	if (nodefs || (test_opt(sb, INIT_INODE_TABLE) &&

		       (sbi->s_li_wait_mult != EXT4_DEF_LI_WAIT_MULT)))

		SEQ_OPTS_PRINT("init_itable=%u", sbi->s_li_wait_mult);

	if (nodefs || sbi->s_max_dir_size_kb)

		SEQ_OPTS_PRINT("max_dir_size_kb=%u", sbi->s_max_dir_size_kb);



	ext4_show_quota_options(seq, sb);

	return 0;

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