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tree-wide: add size limits for tmpfs mounts

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Limit size of various tmpfs mounts to 10% of RAM, except volatile root and /var
to 25%. Another exception is made for /dev (also /devs for PrivateDevices) and
/sys/fs/cgroup since no (or very few) regular files are expected to be used.

In addition, since directories, symbolic links, device specials and xattrs are
not counted towards the size= limit, number of inodes is also limited
correspondingly: 4MB size translates to 1k of inodes (assuming 4k each), 10% of
RAM (using 16GB of RAM as baseline) translates to 400k and 25% to 1M inodes.

Because nr_inodes option can't use ratios like size option, there's an
unfortunate side effect that with small memory systems the limit may be on the
too large side. Also, on an extremely small device with only 256MB of RAM, 10%
of RAM for /run may not be enough for re-exec of PID1 because 16MB of free
space is required.
This commit is contained in:
Topi Miettinen
2020-05-13 00:37:18 +02:00
committed by Lennart Poettering
parent 7cc8fb3ef0
commit 7d85383edb
8 changed files with 63 additions and 45 deletions
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src/shared/mount-util.h
+17
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@@ -6,6 +6,23 @@
#include "macro.h"
/* 4MB for contents of regular files, 64k inodes for directories, symbolic links and device specials,
using large storage array systems as a baseline */
#define TMPFS_LIMITS_DEV ",size=4m,nr_inodes=64k"
/* Very little, if any use expected */
#define TMPFS_LIMITS_EMPTY_OR_ALMOST ",size=4m,nr_inodes=1k"
#define TMPFS_LIMITS_SYS TMPFS_LIMITS_EMPTY_OR_ALMOST
#define TMPFS_LIMITS_SYS_FS_CGROUP TMPFS_LIMITS_EMPTY_OR_ALMOST
/* 10% of RAM (using 16GB of RAM as a baseline) translates to 400k inodes (assuming 4k each) and 25%
translates to 1M inodes */
#define TMPFS_LIMITS_TMP ",size=10%,nr_inodes=400k"
#define TMPFS_LIMITS_DEV_SHM TMPFS_LIMITS_TMP
#define TMPFS_LIMITS_RUN TMPFS_LIMITS_TMP
#define TMPFS_LIMITS_TEMPORARY_FS TMPFS_LIMITS_TMP
#define TMPFS_LIMITS_VAR ",size=25%,nr_inodes=1m"
#define TMPFS_LIMITS_ROOTFS TMPFS_LIMITS_VAR
#define TMPFS_LIMITS_VOLATILE_STATE TMPFS_LIMITS_VAR
int repeat_unmount(const char *path, int flags);
int umount_recursive(const char *target, int flags);
int bind_remount_recursive(const char *prefix, unsigned long new_flags, unsigned long flags_mask, char **blacklist);