[Qemu-devel] Re: [PATCH] fix migration with large mem

[Izik Eidus]

On Tue, 13 Apr 2010 12:33:18 +0300
Izik Eidus <address@hidden> wrote:

> From f881b371e08760a67bf1f5b992a586c3de600f7a Mon Sep 17 00:00:00 2001
> From: Izik Eidus <address@hidden>
> Date: Tue, 13 Apr 2010 12:24:57 +0300
> Subject: [PATCH] fix migration with large mem

Anyone ???


> 
> In cases of guests with large mem that have pages
> that all their bytes content are the same, we will
> spend alot of time reading the memory from the guest
> (is_dup_page())
> 
> It is happening beacuse ram_save_live() function have
> limit of how much we can send to the dest but not how
> much we read from it, and in cases we have many is_dup_page()
> hits, we might read huge amount of data without updating important
> stuff like the timers...
> 
> The guest lose all its repsonsibility and have many softlock ups
> inside itself.
> 
> this patch add limit on the size we can read from the guest each
> iteration.
> 
>     Thanks.
> 
> Signed-off-by: Izik Eidus <address@hidden>
> ---
>  arch_init.c |    6 +++++-
>  1 files changed, 5 insertions(+), 1 deletions(-)
> 
> diff --git a/arch_init.c b/arch_init.c
> index cfc03ea..e27b1a0 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -88,6 +88,8 @@ const uint32_t arch_type = QEMU_ARCH;
>  #define RAM_SAVE_FLAG_PAGE   0x08
>  #define RAM_SAVE_FLAG_EOS    0x10
>  
> +#define MAX_SAVE_BLOCK_READ 10 * 1024 * 1024
> +
>  static int is_dup_page(uint8_t *page, uint8_t ch)
>  {
>      uint32_t val = ch << 24 | ch << 16 | ch << 8 | ch;
> @@ -175,6 +177,7 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, 
> void *opaque)
>      uint64_t bytes_transferred_last;
>      double bwidth = 0;
>      uint64_t expected_time = 0;
> +    int data_read = 0;
>  
>      if (stage < 0) {
>          cpu_physical_memory_set_dirty_tracking(0);
> @@ -205,10 +208,11 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, 
> void *opaque)
>      bytes_transferred_last = bytes_transferred;
>      bwidth = qemu_get_clock_ns(rt_clock);
>  
> -    while (!qemu_file_rate_limit(f)) {
> +    while (!qemu_file_rate_limit(f) && data_read < MAX_SAVE_BLOCK_READ) {
>          int ret;
>  
>          ret = ram_save_block(f);
> +        data_read += ret * TARGET_PAGE_SIZE;
>          bytes_transferred += ret * TARGET_PAGE_SIZE;
>          if (ret == 0) { /* no more blocks */
>              break;