The slurp_fd() function allocates memory and uses the read() system call.
This results in double memory consumption for image and initrd:
1) Memory allocated in user space by the kexec tool
2) Memory allocated in kernel by the kexec() system call
The following illustrates the use case that we have on s390x:
1) Boot a 4 GB Linux system
2) Copy kernel and 1,5 GB ramdisk from external source into tmpfs (ram)
3) Use kexec to boot kernel with ramdisk
Therefore for kexec runtime we need:
1,5 GB (tmpfs) + 1,5 GB (kexec malloc) + 1,5 GB (kernel memory) = 4,5 GB
This patch introduces slurp_file_mmap() which for "normal" files uses
mmap() instead of malloc()/read(). This reduces the runtime memory
consumption of the kexec tool as follows:
1,5 GB (tmpfs) + 1,5 GB (kernel memory) = 3 GB
Signed-off-by: Michael Holzheu <holzheu at linux.vnet.ibm.com>
Reviewed-by: Dave Young <dyoung at redhat.com>
---
kexec/arch/s390/kexec-image.c | 2 +-
kexec/kexec.c | 31 ++++++++++++++++++++++++++++---
kexec/kexec.h | 1 +
3 files changed, 30 insertions(+), 4 deletions(-)
--- a/kexec/arch/s390/kexec-image.c
+++ b/kexec/arch/s390/kexec-image.c
@@ -101,7 +101,7 @@ image_s390_load(int argc, char **argv, c
* we load the ramdisk directly behind the image with 1 MiB alignment.
*/
if (ramdisk) {
- rd_buffer = slurp_file(ramdisk, &ramdisk_len);
+ rd_buffer = slurp_file_mmap(ramdisk, &ramdisk_len);
if (rd_buffer == NULL) {
fprintf(stderr, "Could not read ramdisk.\n");
return -1;
--- a/kexec/kexec.c
+++ b/kexec/kexec.c
@@ -29,6 +29,7 @@
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/reboot.h>
+#include <sys/mman.h>
#include <unistd.h>
#include <fcntl.h>
#ifndef _O_BINARY
@@ -514,7 +515,8 @@ static char *slurp_fd(int fd, const char
return buf;
}
-char *slurp_file(const char *filename, off_t *r_size)
+static char *slurp_file_generic(const char *filename, off_t *r_size,
+ int use_mmap)
{
int fd;
char *buf;
@@ -552,11 +554,17 @@ char *slurp_file(const char *filename, o
if (err < 0)
die("Can not seek to the begin of file %s: %s\n",
filename, strerror(errno));
+ buf = slurp_fd(fd, filename, size, &nread);
} else {
size = stats.st_size;
+ if (use_mmap) {
+ buf = mmap(NULL, size, PROT_READ|PROT_WRITE,
+ MAP_PRIVATE, fd, 0);
+ nread = size;
+ } else {
+ buf = slurp_fd(fd, filename, size, &nread);
+ }
}
-
- buf = slurp_fd(fd, filename, size, &nread);
if (!buf)
die("Cannot read %s", filename);
@@ -567,6 +575,23 @@ char *slurp_file(const char *filename, o
return buf;
}
+/*
+ * Read file into malloced buffer.
+ */
+char *slurp_file(const char *filename, off_t *r_size)
+{
+ return slurp_file_generic(filename, r_size, 0);
+}
+
+/*
+ * Map "normal" file or read "character device" into malloced buffer.
+ * You must not use free, realloc, etc. for the returned buffer.
+ */
+char *slurp_file_mmap(const char *filename, off_t *r_size)
+{
+ return slurp_file_generic(filename, r_size, 1);
+}
+
/* This functions reads either specified number of bytes from the file or
lesser if EOF is met. */
--- a/kexec/kexec.h
+++ b/kexec/kexec.h
@@ -253,6 +253,7 @@ extern void die(const char *fmt, ...)
extern void *xmalloc(size_t size);
extern void *xrealloc(void *ptr, size_t size);
extern char *slurp_file(const char *filename, off_t *r_size);
+extern char *slurp_file_mmap(const char *filename, off_t *r_size);
extern char *slurp_file_len(const char *filename, off_t size, off_t *nread);
extern char *slurp_decompress_file(const char *filename, off_t *r_size);
extern unsigned long virt_to_phys(unsigned long addr);
