Re: [PATCH v3 2/3] mm: smaps*: extend smap_gather_stats to support specified beginning

[Steven Price]

On 15/08/2020 07:20, Chinwen Chang wrote:
> Extend smap_gather_stats to support indicated beginning address at
> which it should start gathering. To achieve the goal, we add a new
> parameter @start assigned by the caller and try to refactor it for
> simplicity.
>
> If @start is 0, it will use the range of @vma for gathering.
>
> Change since v2:
> - This is a new change to make the retry behavior of smaps_rollup
> - more complete as suggested by Michel [1]
>
> [1] https://lore.kernel.org/lkml/CANN689FtCsC71cjAjs0GPspOhgo_HRj+diWsoU1wr98YPktgWg@xxxxxxxxxxxxxx/
>
> Signed-off-by: Chinwen Chang <chinwen.chang@xxxxxxxxxxxx>
> CC: Michel Lespinasse <walken@xxxxxxxxxx>
> CC: Steven Price <steven.price@xxxxxxx>

LGTM

Reviewed-by: Steven Price <steven.price@xxxxxxx>

Steve

> ---
>   fs/proc/task_mmu.c | 30 ++++++++++++++++++++++--------
>   1 file changed, 22 insertions(+), 8 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index dbda449..76e623a 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -723,9 +723,21 @@ static int smaps_hugetlb_range(pte_t *pte, unsigned long hmask,
>   	.pte_hole		= smaps_pte_hole,
>   };
>   
> +/*
> + * Gather mem stats from @vma with the indicated beginning
> + * address @start, and keep them in @mss.
> + *
> + * Use vm_start of @vma as the beginning address if @start is 0.
> + */
>   static void smap_gather_stats(struct vm_area_struct *vma,
> -			     struct mem_size_stats *mss)
> +		struct mem_size_stats *mss, unsigned long start)
>   {
> +	const struct mm_walk_ops *ops = &smaps_walk_ops;
> +
> +	/* Invalid start */
> +	if (start >= vma->vm_end)
> +		return;
> +
>   #ifdef CONFIG_SHMEM
>   	/* In case of smaps_rollup, reset the value from previous vma */
>   	mss->check_shmem_swap = false;
> @@ -742,18 +754,20 @@ static void smap_gather_stats(struct vm_area_struct *vma,
>   		 */
>   		unsigned long shmem_swapped = shmem_swap_usage(vma);
>   
> -		if (!shmem_swapped || (vma->vm_flags & VM_SHARED) ||
> -					!(vma->vm_flags & VM_WRITE)) {
> +		if (!start && (!shmem_swapped || (vma->vm_flags & VM_SHARED) ||
> +					!(vma->vm_flags & VM_WRITE))) {
>   			mss->swap += shmem_swapped;
>   		} else {
>   			mss->check_shmem_swap = true;
> -			walk_page_vma(vma, &smaps_shmem_walk_ops, mss);
> -			return;
> +			ops = &smaps_shmem_walk_ops;
>   		}
>   	}
>   #endif
>   	/* mmap_lock is held in m_start */
> -	walk_page_vma(vma, &smaps_walk_ops, mss);
> +	if (!start)
> +		walk_page_vma(vma, ops, mss);
> +	else
> +		walk_page_range(vma->vm_mm, start, vma->vm_end, ops, mss);
>   }
>   
>   #define SEQ_PUT_DEC(str, val) \
> @@ -805,7 +819,7 @@ static int show_smap(struct seq_file *m, void *v)
>   
>   	memset(&mss, 0, sizeof(mss));
>   
> -	smap_gather_stats(vma, &mss);
> +	smap_gather_stats(vma, &mss, 0);
>   
>   	show_map_vma(m, vma);
>   
> @@ -854,7 +868,7 @@ static int show_smaps_rollup(struct seq_file *m, void *v)
>   	hold_task_mempolicy(priv);
>   
>   	for (vma = priv->mm->mmap; vma; vma = vma->vm_next) {
> -		smap_gather_stats(vma, &mss);
> +		smap_gather_stats(vma, &mss, 0);
>   		last_vma_end = vma->vm_end;
>   	}
>