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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>
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@ -375,6 +375,16 @@ dioread_nolock locking. If the dioread_nolock option is specified
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Because of the restrictions this options comprises
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it is off by default (e.g. dioread_lock).
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max_dir_size_kb=n This limits the size of directories so that any
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attempt to expand them beyond the specified
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limit in kilobytes will cause an ENOSPC error.
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This is useful in memory constrained
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environments, where a very large directory can
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cause severe performance problems or even
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provoke the Out Of Memory killer. (For example,
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if there is only 512mb memory available, a 176mb
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directory may seriously cramp the system's style.)
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i_version Enable 64-bit inode version support. This option is
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off by default.
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@ -1243,6 +1243,7 @@ struct ext4_sb_info {
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unsigned int s_mb_order2_reqs;
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unsigned int s_mb_group_prealloc;
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unsigned int s_max_writeback_mb_bump;
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unsigned int s_max_dir_size_kb;
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/* where last allocation was done - for stream allocation */
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unsigned long s_mb_last_group;
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unsigned long s_mb_last_start;
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@ -55,6 +55,13 @@ static struct buffer_head *ext4_append(handle_t *handle,
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{
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struct buffer_head *bh;
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if (unlikely(EXT4_SB(inode->i_sb)->s_max_dir_size_kb &&
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((inode->i_size >> 10) >=
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EXT4_SB(inode->i_sb)->s_max_dir_size_kb))) {
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*err = -ENOSPC;
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return NULL;
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}
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*block = inode->i_size >> inode->i_sb->s_blocksize_bits;
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bh = ext4_bread(handle, inode, *block, 1, err);
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@ -1230,6 +1230,7 @@ enum {
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Opt_inode_readahead_blks, Opt_journal_ioprio,
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Opt_dioread_nolock, Opt_dioread_lock,
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Opt_discard, Opt_nodiscard, Opt_init_itable, Opt_noinit_itable,
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Opt_max_dir_size_kb,
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};
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static const match_table_t tokens = {
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@ -1303,6 +1304,7 @@ static const match_table_t tokens = {
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{Opt_init_itable, "init_itable=%u"},
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{Opt_init_itable, "init_itable"},
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{Opt_noinit_itable, "noinit_itable"},
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{Opt_max_dir_size_kb, "max_dir_size_kb=%u"},
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{Opt_removed, "check=none"}, /* mount option from ext2/3 */
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{Opt_removed, "nocheck"}, /* mount option from ext2/3 */
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{Opt_removed, "reservation"}, /* mount option from ext2/3 */
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@ -1483,6 +1485,7 @@ static const struct mount_opts {
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{Opt_jqfmt_vfsold, QFMT_VFS_OLD, MOPT_QFMT},
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{Opt_jqfmt_vfsv0, QFMT_VFS_V0, MOPT_QFMT},
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{Opt_jqfmt_vfsv1, QFMT_VFS_V1, MOPT_QFMT},
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{Opt_max_dir_size_kb, 0, MOPT_GTE0},
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{Opt_err, 0, 0}
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};
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@ -1598,6 +1601,8 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
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if (!args->from)
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arg = EXT4_DEF_LI_WAIT_MULT;
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sbi->s_li_wait_mult = arg;
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} else if (token == Opt_max_dir_size_kb) {
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sbi->s_max_dir_size_kb = arg;
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} else if (token == Opt_stripe) {
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sbi->s_stripe = arg;
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} else if (m->flags & MOPT_DATAJ) {
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@ -1829,6 +1834,8 @@ static int _ext4_show_options(struct seq_file *seq, struct super_block *sb,
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if (nodefs || (test_opt(sb, INIT_INODE_TABLE) &&
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(sbi->s_li_wait_mult != EXT4_DEF_LI_WAIT_MULT)))
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SEQ_OPTS_PRINT("init_itable=%u", sbi->s_li_wait_mult);
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if (nodefs || sbi->s_max_dir_size_kb)
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SEQ_OPTS_PRINT("max_dir_size_kb=%u", sbi->s_max_dir_size_kb);
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ext4_show_quota_options(seq, sb);
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return 0;
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