[CRIU] [PATCH v3 05/12] shmem: implement used and dirty pages tracking

[Pavel Emelyanov]

On 08/07/2016 04:11 PM, Eugene Batalov wrote:
> From: Fyodor Bocharov <bocharovfedor at gmail.com>
> 
> To track anon shared vma pages usage we create a bitmap for it.
> Each bit in this bitmap corresponds to particular page in vma. Bit with
> value of 1 in this map states that page is used. Bit 0 states that the
> page wasn't ever used by any dumpee process.
> Page is considered used if it has at least one PME_PRESENT or PME_SWAP
> bit set in any dumpee process pagemap.
> Pages usage tracking allows us not to dump unused pages at all.
> 
> To track anon shared vma pages dirtiness we create a bitmap for it.
> Each bit in this bitmap corresponds to particular page in vma. Bit with
> value of 1 in this map states that page is dirty. Bit 0 states that the
> page is clean.
> Page is considered dirty if it has at least one PME_SOFT_DIRTY bit set in
> any dumpee process pagemap.
> Dirty pages tracking allows not to dump used pages on incremental dumps
> if pages contents haven't changed.
> 
> Signed-off-by: Fyodor Bocharov <fbocharov at yandex.ru>
> Signed-off-by: Eugene Batalov <eabatalov89 at gmail.com>
> ---
>  criu/shmem.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 59 insertions(+), 5 deletions(-)
> 
> diff --git a/criu/shmem.c b/criu/shmem.c
> index f8a3ba3..f59a2e6 100644
> --- a/criu/shmem.c
> +++ b/criu/shmem.c
> @@ -81,6 +81,8 @@ struct shmem_info {
>  		struct { /* For dump */
>  			unsigned long	start;
>  			unsigned long	end;
> +			unsigned long	*pdirty_map;
> +			unsigned long	*pused_map;
>  		};
>  	};
>  };
> @@ -120,6 +122,52 @@ static struct shmem_info *shmem_find(unsigned long shmid)
>  	return NULL;
>  }
>  
> +#define BLOCKS_CNT(size, block_size) \
> +	(((size) + (block_size) - 1) / (block_size))

This is DIV_ROUND_UP helper we have already.

> +
> +static int expand_shmem(struct shmem_info *si, unsigned long new_size)
> +{
> +	unsigned long nr_pages, nr_map_items, map_size,
> +				nr_new_map_items, new_map_size;
> +
> +	nr_pages = BLOCKS_CNT(si->size, PAGE_SIZE);
> +	nr_map_items = BLOCKS_CNT(nr_pages, sizeof(*si->pdirty_map) * 8);

nr_map_items = BITS_TO_LONGS() :)

> +	map_size = nr_map_items * sizeof(*si->pdirty_map);
> +
> +	nr_pages = BLOCKS_CNT(new_size, PAGE_SIZE);
> +	nr_new_map_items = BLOCKS_CNT(nr_pages, sizeof(*si->pdirty_map) * 8);
> +	new_map_size = nr_new_map_items * sizeof(*si->pdirty_map);
> +
> +	BUG_ON(new_map_size < map_size);
> +
> +	si->pdirty_map = xrealloc(si->pdirty_map, new_map_size);
> +	if (!si->pdirty_map)
> +		return -1;
> +	memzero(si->pdirty_map + nr_map_items, new_map_size - map_size);
> +
> +	si->pused_map = xrealloc(si->pused_map, new_map_size);
> +	if (!si->pused_map)
> +		return -1;
> +	memzero(si->pused_map + nr_map_items, new_map_size - map_size);
> +
> +	si->size = new_size;
> +	return 0;
> +}
> +
> +static void update_shmem_pmaps(struct shmem_info *si, u64 *map,
> +		unsigned long off)
> +{
> +	unsigned long p, pcount, poff;
> +
> +	pcount = BLOCKS_CNT(si->size - off, PAGE_SIZE);
> +	poff = BLOCKS_CNT(off, PAGE_SIZE);
> +	for (p = 0; p < pcount; ++p) {
> +		if (map[p] & PME_SOFT_DIRTY)
> +			set_bit(p + poff, si->pdirty_map);
> +		if ((map[p] & PME_PRESENT) || (map[p] & PME_SWAP))

Absolutely the same check is used in should_dump_page(), please, factor
out them.

> +			set_bit(p + poff, si->pused_map);
> +	}
> +}
>  
>  int collect_sysv_shmem(unsigned long shmid, unsigned long size)
>  {
> @@ -489,26 +537,32 @@ int add_shmem_area(pid_t pid, VmaEntry *vma, u64 *map)
>  {
>  	struct shmem_info *si;
>  	unsigned long size = vma->pgoff + (vma->end - vma->start);
> -	(void)map;
>  
>  	si = shmem_find(vma->shmid);
>  	if (si) {
> -		if (si->size < size)
> -			si->size = size;
> +		if (si->size < size) {
> +			if (expand_shmem(si, size))
> +				return -1;
> +		}
> +		update_shmem_pmaps(si, map, vma->pgoff);
> +
>  		return 0;
>  	}
>  
> -	si = xmalloc(sizeof(*si));
> +	si = xzalloc(sizeof(*si));
>  	if (!si)
>  		return -1;
>  
> -	si->size = size;
>  	si->pid = pid;
>  	si->start = vma->start;
>  	si->end = vma->end;
>  	si->shmid = vma->shmid;
>  	shmem_hash_add(si);
>  
> +	if (expand_shmem(si, size))
> +		return -1;
> +	update_shmem_pmaps(si, map, vma->pgoff);
> +
>  	return 0;
>  }
>  
>