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Date: Fri, 10 Aug 2012 21:22:39 -0600
From: Andreas Dilger <adilger@...mcloud.com>
To: Theodore Ts'o <tytso@....edu>
Cc: Ext4 Developers List <linux-ext4@...r.kernel.org>,
Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH -v2] ext4: add max_dir_size_kb mount option
On 2012-08-10, at 19:40, Theodore Ts'o <tytso@....edu> wrote:
> 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.
In our patch, it returns EFBIG, since it isn't really a case of being out of space for blocks or inodes.
Cheers, Andreas
> Google-Bug-Id: 6863013
>
> Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> ---
> Documentation/filesystems/ext4.txt | 4 ++++
> fs/ext4/ext4.h | 1 +
> fs/ext4/namei.c | 7 +++++++
> fs/ext4/super.c | 7 +++++++
> 4 files changed, 19 insertions(+)
>
> diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
> index 1b7f9ac..43b80b5 100644
> --- a/Documentation/filesystems/ext4.txt
> +++ b/Documentation/filesystems/ext4.txt
> @@ -375,6 +375,10 @@ 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.
> +
> i_version Enable 64-bit inode version support. This option is
> off by default.
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index c3411d4..7c0841e 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -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;
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index 2a42cc0..7450ff0 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -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);
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 56bcaec..5896dcb 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -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;
> --
> 1.7.12.rc0.22.gcdd159b
>
> --
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