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: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 5984989..5a97e59 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1230,6 +1230,7 @@
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 @@
{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 @@
{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 @@
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 @@
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;