Adds a kernel configuration option and command line parameter to
specify the size of the shmem filesystem. It is currently hard-coded
to 50% of memory. Users should have the option to set this value as
they see fit.
A specific case where this is necessary would be if the initramfs were
larger than half of the memory, such as a 2.5GB filesystem with 4GB of
memory. Without this option, this causes a kernel panic. With this
option, the user may specify something like 75%, which would allow the
filesystem into memory, while still leaving enough resources to run
a functioning system.
This patch creates the SHMEM_SIZE configuration option and the
shmem_size parameter, which may be specified in bytes, human notation
(1G, 100M, etc.) or percentage (75%). The default remains unchanged.
This patch has no impact unless the values are changed.
Signed-off-by: Gary B. Genett <me@xxxxxxxxxxxxxxx>
---
Documentation/admin-guide/kernel-parameters.rst | 1 +
Documentation/admin-guide/kernel-parameters.txt | 5 +++
init/Kconfig | 8 ++++
mm/shmem.c | 57 +++++++++++++++++++++++--
4 files changed, 67 insertions(+), 4 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst
index d05d531b4ec9..33122a6df04f 100644
--- a/Documentation/admin-guide/kernel-parameters.rst
+++ b/Documentation/admin-guide/kernel-parameters.rst
@@ -149,6 +149,7 @@ parameter is applicable::
APPARMOR AppArmor support is enabled.
SERIAL Serial support is enabled.
SH SuperH architecture is enabled.
+ SHMEM Full shmem filesystem is enabled.
SMP The kernel is an SMP kernel.
SPARC Sparc architecture is enabled.
SWSUSP Software suspend (hibernation) is enabled.
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index c7ac2f3ac99f..aeac92577569 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4307,6 +4307,11 @@
shapers= [NET]
Maximal number of shapers.
+ shmem_size= [SHMEM]
+ Size of shmem filesystem. Can be specified as a plain
+ integer, in memory size notation (such as 1024M or 1G),
+ or as a percentage (50%).
+
simeth= [IA-64]
simscsi=
diff --git a/init/Kconfig b/init/Kconfig
index b4daad2bac23..7b07f5c448af 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1537,6 +1537,14 @@ config SHMEM
option replaces shmem and tmpfs with the much simpler ramfs code,
which may be appropriate on small systems without swap.
+config SHMEM_SIZE
+ string "Hard-set the shmem filesystem size"
+ default 0
+ depends on SHMEM
+ help
+ Size of shmem filesystem. Can be specified as a plain integer, in
+ memory size notation (such as 1024M or 1G), or as a percentage (50%).
+
config AIO
bool "Enable AIO support" if EXPERT
default y
diff --git a/mm/shmem.c b/mm/shmem.c
index cd570cc79c76..ad6109524ad1 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -95,6 +95,12 @@ static struct vfsmount *shm_mnt;
/* Symlink up to this size is kmalloc'ed instead of using a swappable page */
#define SHORT_SYMLINK_LEN 128
+/* Default size of shmem filesystem (defaults to 50% of memory) */
+#define SHMEM_SIZE_DEFAULT ((totalram_pages * PAGE_SIZE) / 2)
+/* Final initialized size of shmem filesystem, and stored parameter value */
+unsigned long shmem_size_final;
+char shmem_size_param[20];
+
/*
* shmem_fallocate communicates with shmem_fault or shmem_writepage via
* inode->i_private (with i_mutex making sure that it has only one user at
@@ -123,16 +129,56 @@ struct shmem_options {
};
#ifdef CONFIG_TMPFS
+static void shmem_size_parse(void)
+{
+ char *str, *t;
+
+ sprintf(shmem_size_param, "%s", "0");
+ str = strstr(boot_command_line, "shmem_size=");
+ if (str) {
+ t = strsep(&str, " ");
+ t += 11;
+ sprintf(shmem_size_param, "%s", t);
+ }
+}
+
+static void shmem_size(char *str, char *val)
+{
+ char *rest;
+ unsigned long mem = memparse(val, &rest);
+
+ if (*rest == '%') {
+ mem *= (totalram_pages * PAGE_SIZE);
+ do_div(mem, 100);
+ }
+ if (mem > 0) {
+ pr_info("shmem: found %s value: %s (%ld pages, %ld bytes)\n",
+ str, val, (mem / PAGE_SIZE), mem);
+ shmem_size_final = (mem / PAGE_SIZE);
+ }
+}
+
+static void shmem_size_init(void)
+{
+ char tmp[20];
+
+ sprintf(tmp, "%ld", SHMEM_SIZE_DEFAULT);
+ shmem_size("default", tmp);
+#ifdef CONFIG_SHMEM_SIZE
+ shmem_size("kernel configuration", CONFIG_SHMEM_SIZE);
+#endif
+ shmem_size_parse();
+ shmem_size("kernel parameter", shmem_size_param);
+}
+
static unsigned long shmem_default_max_blocks(void)
{
- return totalram_pages() / 2;
+ return shmem_size_final;
}
static unsigned long shmem_default_max_inodes(void)
{
- unsigned long nr_pages = totalram_pages();
-
- return min(nr_pages - totalhigh_pages(), nr_pages / 2);
+ return min(totalram_pages - totalhigh_pages, shmem_size_final);
}
#endif
@@ -3887,6 +3933,9 @@ int __init shmem_init(void)
{
int error;
+#ifdef CONFIG_TMPFS
+ shmem_size_init();
+#endif
shmem_init_inodecache();
error = register_filesystem(&shmem_fs_type);
--
2.15.2
