Re: [Qemu-devel] [PATCH v3] mem-prealloc: reduce large guest start-up and migration time.

[Paolo Bonzini]

On 23/02/2017 10:56, Jitendra Kolhe wrote:
>      if (sigsetjmp(sigjump, 1)) {
> -        error_setg(errp, "os_mem_prealloc: Insufficient free host memory "
> -            "pages available to allocate guest RAM\n");
> +        memset_thread_failed = true;

This sigsetjmp is not needed, no one can siglongjmp to it.

The SIG_UNBLOCK/SIG_BLOCK in the main thread is not necessary, either.

>      } else {
> -        int i;
>          size_t hpagesize = qemu_fd_getpagesize(fd);
>          size_t numpages = DIV_ROUND_UP(memory, hpagesize);
>  
> -        /* MAP_POPULATE silently ignores failures */
> -        for (i = 0; i < numpages; i++) {
> -            memset(area + (hpagesize * i), 0, 1);
> -        }
> +        /* touch pages simultaneously */
> +        touch_all_pages(area, hpagesize, numpages, smp_cpus);

... and now touch_all_pages can just return memset_thread_failed, which
simplifies the code a bit.

Paolo

> +    }
> +    if (memset_thread_failed) {
> +        error_setg(errp, "os_mem_prealloc: Insufficient free host memory "
> +            "pages available to allocate guest RAM");
>      }