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    SubjectRe: [PATCH 0/4] ksm - dynamic page sharing driver for linux v2
    Hi Izik,

    I've tried your patch set, but ksm doesn't work in my machine.

    I compiled linux patched with the four patches and configured with KSM
    and KVM enabled. After boot with the linux, I run two VMs running linux
    using QEMU with a patch in your mail and started KSM scanner with your
    script, then the host linux caused panic with the following oops.


    == BEGINNING of OOPS
    kernel BUG at arch/x86/mm/highmem_32.c:87!
    invalid opcode: 0000 [#1] SMP
    last sysfs file: /sys/class/net/vnet-ssh2/address
    Dumping ftrace buffer:
    (ftrace buffer empty)
    Modules linked in: netconsole autofs4 nf_conntrack_ipv4 nf_defrag_ipv4
    xt_state nf_conntrack xt_tcpudp ipt_REJECT iptable_filter ip_tables
    x_tables loop kvm_intel kvm iTCO_wdt iTCO_vendor_support igb
    netxen_nic button ext3 jbd mbcache uhci_hcd ohci_hcd ehci_hcd usbcore
    [last unloaded: microcode]

    Pid: 343, comm: kksmd Not tainted
    (2.6.28-rc5-linus-head-20081119-sparsemem #1) X7DWA
    EIP: 0060:[<c041eff9>] EFLAGS: 00010206 CPU: 6
    EIP is at kmap_atomic_prot+0x7d/0xeb
    EAX: c0008d94 EBX: c1ff6240 ECX: 00000163 EDX: 7e000000
    ESI: 00000154 EDI: 00000055 EBP: f5cdbf10 ESP: f5cdbef8
    DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
    Process kksmd (pid: 343, ti=f5cda000 task=f617b140 task.ti=f5cda000)
    Stack:
    7fa12163 fffff000 c204efbc f50479e8 9eb7e000 c08a34d0 f5cdbf18 c041f07a
    f5cdbf28 c048339c 00000000 f5c271e0 f5cdbf30 c04833bc f5cdbfb0 c0483b0d
    f5cdbf50 c0425845 00000000 00000064 00000009 c08a34d0 f5cdbfb0 c06384c1
    Call Trace:
    [<c041f07a>] ? kmap_atomic+0x13/0x15
    [<c048339c>] ? get_pte+0x50/0x63
    [<c04833bc>] ? is_present_pte+0xd/0x1f
    [<c0483b0d>] ? ksm_scan_start+0x9a/0x7ac
    [<c0425845>] ? finish_task_switch+0x29/0xa4
    [<c06384c1>] ? schedule+0x6bf/0x719
    [<c041b3fc>] ? default_spin_lock_flags+0x8/0xc
    [<c043bffa>] ? finish_wait+0x49/0x4e
    [<c04845f4>] ? kthread_ksm_scan_thread+0x0/0xdc
    [<c048462e>] ? kthread_ksm_scan_thread+0x3a/0xdc
    [<c043bf31>] ? autoremove_wake_function+0x0/0x38
    [<c043be3e>] ? kthread+0x40/0x66
    [<c043bdfe>] ? kthread+0x0/0x66
    [<c0404997>] ? kernel_thread_helper+0x7/0x10
    Code: 86 00 00 00 64 a1 04 a0 82 c0 6b c0 0d 8d 3c 30 a1 78 b0 77 c0
    8d 34 bd 00 00 00 00 89 45 ec a1 0c d0 84 c0 29 f0 83 38 00 74 04 <0f>
    0b eb fe c1 ea 1a 8b 04 d5 80 32 8a c0 83 e0 fc 29 c3 c1 fb
    EIP: [<c041eff9>] kmap_atomic_prot+0x7d/0xeb SS:ESP 0068:f5cdbef8
    Kernel panic - not syncing: Fatal exception
    == END of OOPS


    I used a version of linux kernel from linus tree (commit e14c8bf863...
    at Mon Nov 17)
    with a configuration as the attached file and kvm-userspace (commit
    0cf57d569f3...
    at Mon Nov 10). Other configurations are as follows:

    Host: Fedora 8
    Arch: i686
    CPU: Intel(R) Xeon(R) CPU E5410 @ 2.33GHz
    Mem: 2 GB
    Guest: Fedora Core 7, linux-2.6.27
    Cmd: qemu-system-x86_64 -kernel vmlinuz-2.6.27 -initrd
    initrd-2.6.27.img -append ro root=/dev/VolGroup00/LogVol00
    kvm_paravirt=1 loglevel=4 rhgb quiet -hda -M pc -smp 1 -curses -clock
    dynticks -net nic,vlan=0,macaddr=00:00:00:1:11:0,model=virtio -net
    tap,vlan=0,ifname=vnet1,script=no -m 384


    Note that if I disable HIGHMEM of the host kernel, ksm works well.

    Any idea?

    Thanks in advance,
    ozaki-r


    2008/11/17 Izik Eidus <ieidus@redhat.com>:
    > (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.
    > (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 kvm" in
    > the body of a message to majordomo@vger.kernel.org
    > More majordomo info at http://vger.kernel.org/majordomo-info.html
    >
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