Re: [PATCH v2 05/26] mm: gup: allow VM_FAULT_RETRY for multiple times

From: Jerome Glisse <jglisse@redhat.com>
To: Peter Xu <peterx@redhat.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	David Hildenbrand <david@redhat.com>,
	Hugh Dickins <hughd@google.com>, Maya Gokhale <gokhale2@llnl.gov>,
	Pavel Emelyanov <xemul@virtuozzo.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Martin Cracauer <cracauer@cons.org>, Shaohua Li <shli@fb.com>,
	Marty McFadden <mcfadden8@llnl.gov>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Denis Plotnikov <dplotnikov@virtuozzo.com>,
	Mike Rapoport <rppt@linux.vnet.ibm.com>,
	Mel Gorman <mgorman@suse.de>,
	"Kirill A . Shutemov" <kirill@shutemov.name>,
	"Dr . David Alan Gilbert" <dgilbert@redhat.com>
Subject: Re: [PATCH v2 05/26] mm: gup: allow VM_FAULT_RETRY for multiple times
Date: Thu, 21 Feb 2019 11:06:55 -0500	[thread overview]
Message-ID: <20190221160612.GE2813@redhat.com> (raw)
In-Reply-To: <20190212025632.28946-6-peterx@redhat.com>

On Tue, Feb 12, 2019 at 10:56:11AM +0800, Peter Xu wrote:
> This is the gup counterpart of the change that allows the VM_FAULT_RETRY
> to happen for more than once.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: Jérôme Glisse <jglisse@redhat.com>

> ---
>  mm/gup.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index fa75a03204c1..ba387aec0d80 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -528,7 +528,10 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
>  	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);
> +		/*
> +		 * Note: FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_TRIED
> +		 * can co-exist
> +		 */
>  		fault_flags |= FAULT_FLAG_TRIED;
>  	}
>  
> @@ -943,17 +946,23 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
>  		/* VM_FAULT_RETRY triggered, so seek to the faulting offset */
>  		pages += ret;
>  		start += ret << PAGE_SHIFT;
> +		lock_dropped = true;
>  
> +retry:
>  		/*
>  		 * Repeat on the address that fired VM_FAULT_RETRY
> -		 * without FAULT_FLAG_ALLOW_RETRY but with
> +		 * with both FAULT_FLAG_ALLOW_RETRY and
>  		 * FAULT_FLAG_TRIED.
>  		 */
>  		*locked = 1;
> -		lock_dropped = true;
>  		down_read(&mm->mmap_sem);
>  		ret = __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED,
> -				       pages, NULL, NULL);
> +				       pages, NULL, locked);
> +		if (!*locked) {
> +			/* Continue to retry until we succeeded */
> +			BUG_ON(ret != 0);
> +			goto retry;
> +		}
>  		if (ret != 1) {
>  			BUG_ON(ret > 1);
>  			if (!pages_done)
> -- 
> 2.17.1
>