Re: [PATCH 1/4] mm: gup: add FOLL_TRIED

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Oct 01, 2014 at 10:56:34AM +0200, Andrea Arcangeli wrote:
> From: Andres Lagar-Cavilla <andreslc@google.com>

This needs a changelog....

> Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
> Signed-off-by: Andres Lagar-Cavilla <andreslc@google.com>
> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
> ---
>  include/linux/mm.h | 1 +
>  mm/gup.c           | 4 ++++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 8981cc8..0f4196a 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1985,6 +1985,7 @@ static inline struct page *follow_page(struct vm_area_struct *vma,
>  #define FOLL_HWPOISON	0x100	/* check page is hwpoisoned */
>  #define FOLL_NUMA	0x200	/* force NUMA hinting page fault */
>  #define FOLL_MIGRATION	0x400	/* wait for page to replace migration entry */
> +#define FOLL_TRIED	0x800	/* a retry, previous pass started an IO */
>  
>  typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
>  			void *data);
> diff --git a/mm/gup.c b/mm/gup.c
> index 91d044b..af7ea3e 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -281,6 +281,10 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
>  		fault_flags |= FAULT_FLAG_ALLOW_RETRY;
>  	if (*flags & FOLL_NOWAIT)
>  		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
> +	if (*flags & FOLL_TRIED) {
> +		VM_WARN_ON_ONCE(fault_flags & FAULT_FLAG_ALLOW_RETRY);
> +		fault_flags |= FAULT_FLAG_TRIED;
> +	}
>  
>  	ret = handle_mm_fault(mm, vma, address, fault_flags);
>  	if (ret & VM_FAULT_ERROR) {

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