From df981d03eeff7971ac7e6ff37000bfa702327ef1 Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Fri, 17 Aug 2012 09:48:17 -0400 Subject: [PATCH] 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" --- Documentation/filesystems/ext4.txt | 10 ++++++++++ fs/ext4/ext4.h | 1 + fs/ext4/namei.c | 7 +++++++ fs/ext4/super.c | 7 +++++++ 4 files changed, 25 insertions(+) diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt index 1b7f9acbcbbe..104322bf378c 100644 --- a/Documentation/filesystems/ext4.txt +++ b/Documentation/filesystems/ext4.txt @@ -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. diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index c3411d4ce2da..7c0841ecde6c 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 2a42cc04466f..7450ff01c3c4 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 598498904035..5a97e590692d 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; -- 2.30.2