Izik Eidus <[EMAIL PROTECTED]> writes: > (From v1 to v2 the main change is much more documentation) > > KSM is a linux driver that allows dynamicly sharing identical memory > pages between one or more processes. > > Unlike tradtional page sharing that is made at the allocation of the > memory, ksm do it dynamicly after the memory was created. > Memory is periodically scanned; identical pages are identified and > merged. > The sharing is unnoticeable by the process that use this memory. > (the shared pages are marked as readonly, and in case of write > do_wp_page() take care to create new copy of the page) > > This driver is very useful for KVM as in cases of runing multiple guests > operation system of the same type. Hi Izik, approach that was used in the driver commonly known as content based search. Where are several variants of it most commons are: 1: with guest TM support 2: w/o guest vm support. You have implemented second one, but seems it already was patented http://www.google.com/patents?vid=USPAT6789156 I'm not a lawyer but IMHO we have direct conflict here. >From other point of view they have patented the WEEL, but at least we have to know about this. > (For desktop work loads we have achived more than x2 memory overcommit > (more like x3)) > > This driver have found users other than KVM, for example CERN, > Fons Rademakers: > "on many-core machines we run one large detector simulation program per core. > These simulation programs are identical but run each in their own process and > need about 2 - 2.5 GB RAM. > We typically buy machines with 2GB RAM per core and so have a problem to run > one of these programs per core. > Of the 2 - 2.5 GB about 700MB is identical data in the form of magnetic field > maps, detector geometry, etc. > Currently people have been trying to start one program, initialize the > geometry > and field maps and then fork it N times, to have the data shared. > With KSM this would be done automatically by the system so it sounded > extremely > attractive when Andrea presented it." > > (We have are already started to test KSM on their systems...) > > KSM can run as kernel thread or as userspace application or both > > example for how to control the kernel thread: > > #include <stdio.h> > #include <stdlib.h> > #include <string.h> > #include <sys/types.h> > #include <sys/stat.h> > #include <sys/ioctl.h> > #include <fcntl.h> > #include <sys/mman.h> > #include <unistd.h> > #include "ksm.h" > > int main(int argc, char *argv[]) > { > int fd; > int used = 0; > int fd_start; > struct ksm_kthread_info info; > > > if (argc < 2) { > fprintf(stderr, > "usage: %s {start npages sleep | stop | info}\n", > argv[0]); > exit(1); > } > > fd = open("/dev/ksm", O_RDWR | O_TRUNC, (mode_t)0600); > if (fd == -1) { > fprintf(stderr, "could not open /dev/ksm\n"); > exit(1); > } > > if (!strncmp(argv[1], "start", strlen(argv[1]))) { > used = 1; > if (argc < 4) { > fprintf(stderr, > "usage: %s start npages_to_scan max_pages_to_merge sleep\n", > argv[0]); > exit(1); > } > info.pages_to_scan = atoi(argv[2]); > info.max_pages_to_merge = atoi(argv[3]); > info.sleep = atoi(argv[4]); > info.flags = ksm_control_flags_run; > > fd_start = ioctl(fd, KSM_START_STOP_KTHREAD, &info); > if (fd_start == -1) { > fprintf(stderr, "KSM_START_KTHREAD failed\n"); > exit(1); > } > printf("created scanner\n"); > } > > if (!strncmp(argv[1], "stop", strlen(argv[1]))) { > used = 1; > info.flags = 0; > fd_start = ioctl(fd, KSM_START_STOP_KTHREAD, &info); > printf("stopped scanner\n"); > } > > if (!strncmp(argv[1], "info", strlen(argv[1]))) { > used = 1; > ioctl(fd, KSM_GET_INFO_KTHREAD, &info); > printf("flags %d, pages_to_scan %d npages_merge %d, sleep_time %d\n", > info.flags, info.pages_to_scan, info.max_pages_to_merge, info.sleep); > } > > if (!used) > fprintf(stderr, "unknown command %s\n", argv[1]); > > return 0; > } > > example of how to register qemu to ksm (or any userspace application) > > diff --git a/qemu/vl.c b/qemu/vl.c > index 4721fdd..7785bf9 100644 > --- a/qemu/vl.c > +++ b/qemu/vl.c > @@ -21,6 +21,7 @@ > * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER > * DEALINGS IN > * THE SOFTWARE. > */ > +#include "ksm.h" > #include "hw/hw.h" > #include "hw/boards.h" > #include "hw/usb.h" > @@ -5799,6 +5800,37 @@ static void termsig_setup(void) > > #endif > > +int ksm_register_memory(void) > +{ > + int fd; > + int ksm_fd; > + int r = 1; > + struct ksm_memory_region ksm_region; > + > + fd = open("/dev/ksm", O_RDWR | O_TRUNC, (mode_t)0600); > + if (fd == -1) > + goto out; > + > + ksm_fd = ioctl(fd, KSM_CREATE_SHARED_MEMORY_AREA); > + if (ksm_fd == -1) > + goto out_free; > + > + ksm_region.npages = phys_ram_size / TARGET_PAGE_SIZE; > + ksm_region.addr = phys_ram_base; > + r = ioctl(ksm_fd, KSM_REGISTER_MEMORY_REGION, &ksm_region); > + if (r) > + goto out_free1; > + > + return r; > + > +out_free1: > + close(ksm_fd); > +out_free: > + close(fd); > +out: > + return r; > +} > + > int main(int argc, char **argv) > { > #ifdef CONFIG_GDBSTUB > @@ -6735,6 +6767,8 @@ int main(int argc, char **argv) > /* init the dynamic translator */ > cpu_exec_init_all(tb_size * 1024 * 1024); > > + ksm_register_memory(); > + > bdrv_init(); > > /* we always create the cdrom drive, even if no disk is there */ > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to [EMAIL PROTECTED] > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
> LocalWords: Izik vm WEEL -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
