[CRIU] [PATCH] criu: pagemap-cache -- Drop off greedy mode

[Pavel Emelyanov]

On 05/05/2016 11:55 PM, Cyrill Gorcunov wrote:
> It never worked properly before and correct
> implementation requires interactions with
> parasite page fetching. 

Please write why it doesn't work, otherwise once (if) we get back to
this we'll not be able to find out what the problem was easily.

> So simply zap it for a while.
> 
> Reported-by: Pavel Emelyanov <xemul at virtuozzo.com>
> Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
> ---
>  criu/pagemap-cache.c | 38 ++++++++++++++++++--------------------
>  1 file changed, 18 insertions(+), 20 deletions(-)
> 
> diff --git a/criu/pagemap-cache.c b/criu/pagemap-cache.c
> index e38bc3fb6b16..28bd8caa1f97 100644
> --- a/criu/pagemap-cache.c
> +++ b/criu/pagemap-cache.c
> @@ -48,9 +48,19 @@ int pmc_init(pmc_t *pmc, pid_t pid, const struct list_head *vma_head, size_t siz
>  		goto err;
>  
>  	if (kdat.pmap == PM_DISABLED) {
> -		pmc->fd = -1;
> -		pr_warn("No pagemap for %d available, "
> -				"switching to greedy mode\n", pid);
> +		/*
> +		 * FIXME We might need to implement greedy
> +		 * mode via reading all pages available inside
> +		 * parasite.
> +		 *
> +		 * Actually since linux-4.4 the pagemap file
> +		 * is available for usernamespace with hiding
> +		 * PFNs but providing page attributes, so other
> +		 * option simply require kernel 4.4 and above
> +		 * for usernamespace support.
> +		 */
> +		pr_err("No pagemap for %d available\n", pid);
> +		goto err;
>  	} else {
>  		pmc->fd = open_proc(pid, "pagemap");
>  		if (pmc->fd < 0)
> @@ -130,24 +140,12 @@ static int pmc_fill_cache(pmc_t *pmc, const struct vma_area *vma)
>  
>  	size_map = PAGEMAP_LEN(pmc->end - pmc->start);
>  	BUG_ON(pmc->map_len < size_map);
> +	BUG_ON(pmc->fd < 0);
>  
> -	if (unlikely(pmc->fd < 0)) {
> -		u64 pme = PME_PRESENT;
> -		size_t i;
> -
> -		/*
> -		 * We don't have access to the dumpee pagemap so fill
> -		 * everything as present. It's better than refuse
> -		 * to dump because it simply disables optimisation.
> -		 */
> -		for (i = 0; i < (size_map / sizeof(pme)); i++)
> -			pmc->map[i] = pme;
> -	} else {
> -		if (pread(pmc->fd, pmc->map, size_map, PAGEMAP_PFN_OFF(pmc->start)) != size_map) {
> -			pmc_zap(pmc);
> -			pr_perror("Can't read %d's pagemap file", pmc->pid);
> -			return -1;
> -		}
> +	if (pread(pmc->fd, pmc->map, size_map, PAGEMAP_PFN_OFF(pmc->start)) != size_map) {
> +		pmc_zap(pmc);
> +		pr_perror("Can't read %d's pagemap file", pmc->pid);
> +		return -1;
>  	}
>  
>  	return 0;
>