diff options
| author | Michael Holzheu <holzheu@linux.vnet.ibm.com> | 2015-09-04 14:11:59 +0200 |
|---|---|---|
| committer | Simon Horman <horms@verge.net.au> | 2015-09-07 15:43:52 +0900 |
| commit | 7ab842d8a004f6cd75a9d7b3528e4a70819ce4ef (patch) | |
| tree | df78ae7aa062cd131da46e4b6ed5f0cc2be0d701 | |
| parent | a304e2d82a8c3e4f66d0707118bc53704b5d9c59 (diff) | |
kexec: use mmap instead of read for slurp_file()
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
Therefore use mmap() for non-character devices to reduce the runtime
memory consumption of the kexec tool.
The following use case illustrates the usefulness of this patch a bit more:
1) Boot a 4 GB Linux system
2) Read kernel and 1,5 GB ramdisk from external source into local tmpfs (ram)
3) kexec the kernel and ramdisk
Without this patch for the kexec runtime we need:
1,5 GB (tmpfs) + 1,5 GB (kexec malloc) + 1,5 GB (kernel memory) = 4,5 GB
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Simon Horman <horms@verge.net.au>
| -rw-r--r-- | kexec/kexec.c | 8 |
1 files changed, 5 insertions, 3 deletions
diff --git a/kexec/kexec.c b/kexec/kexec.c index b9f1816..ff024f3 100644 --- a/kexec/kexec.c +++ b/kexec/kexec.c @@ -26,6 +26,7 @@ #include <stdlib.h> #include <errno.h> #include <limits.h> +#include <sys/mman.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/reboot.h> @@ -552,11 +553,12 @@ char *slurp_file(const char *filename, off_t *r_size) 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; + size = nread = stats.st_size; + buf = mmap(NULL, size, + PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0); } - - buf = slurp_fd(fd, filename, size, &nread); if (!buf) die("Cannot read %s", filename); |