linux-kernel - Re: [PATCH] mm, dax: VMA with vm_ops->pfn

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Date:	Tue, 01 Sep 2015 13:54:26 +0300
From:	Boaz Harrosh <boaz@...xistor.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>
CC:	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org,
	Yigal Korman <yigal@...xistor.com>, Jan Kara <jack@...e.cz>,
	Dave Chinner <david@...morbit.com>
Subject: Re: [PATCH] mm, dax: VMA with vm_ops->pfn_mkwrite wants to be write-notified

On 09/01/2015 01:22 PM, Kirill A. Shutemov wrote:
> For VM_PFNMAP and VM_MIXEDMAP we use vm_ops->pfn_mkwrite instead of
> vm_ops->page_mkwrite to notify abort write access. This means we want
> vma->vm_page_prot to be write-protected if the VMA provides this vm_ops.
> 

Hi Kirill

I will test with this right away and ACK on this.

Hmm so are you saying we might be missing some buffer modifications right now.

What would be a theoretical scenario that will cause these missed events?
I would like to put a test in our test rigs that should fail today and this
patch fixes.

[In our system every modified pmem block is also RDMAed to a remote
 pmem for HA, a missed modification will make the two copies unsynced]

Thanks for catching this
Boaz

> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Yigal Korman <yigal@...xistor.com>
> Cc: Boaz Harrosh <boaz@...xistor.com>
> Cc: Matthew Wilcox <matthew.r.wilcox@...el.com>
> Cc: Jan Kara <jack@...e.cz>
> Cc: Dave Chinner <david@...morbit.com>
> ---
>  mm/mmap.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index df6d5f07035b..3f78bceefe5a 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1498,7 +1498,8 @@ int vma_wants_writenotify(struct vm_area_struct *vma)
>  		return 0;
>  
>  	/* The backer wishes to know when pages are first written to? */
> -	if (vma->vm_ops && vma->vm_ops->page_mkwrite)
> +	if (vma->vm_ops &&
> +			(vma->vm_ops->page_mkwrite || vma->vm_ops->pfn_mkwrite))
>  		return 1;
>  
>  	/* The open routine did something to the protections that pgprot_modify
> 

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