Re: [PATCH v6 06/13] mm, dev_pagemap: Do not clear ->mapping on final put

[Dave Jiang]

Jerome,
Is it possible to get an ack for this? Thanks!

On 07/13/2018 09:50 PM, Dan Williams wrote:
> MEMORY_DEVICE_FS_DAX relies on typical page semantics whereby ->mapping
> is only ever cleared by truncation, not final put.
> 
> Without this fix dax pages may forget their mapping association at the
> end of every page pin event.
> 
> Move this atypical behavior that HMM wants into the HMM ->page_free()
> callback.
> 
> Cc: <stable@xxxxxxxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> Fixes: d2c997c0f145 ("fs, dax: use page->mapping...")
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> ---
>  kernel/memremap.c |    1 -
>  mm/hmm.c          |    2 ++
>  2 files changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/memremap.c b/kernel/memremap.c
> index 5857267a4af5..62603634a1d2 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -339,7 +339,6 @@ void __put_devmap_managed_page(struct page *page)
>  		__ClearPageActive(page);
>  		__ClearPageWaiters(page);
>  
> -		page->mapping = NULL;
>  		mem_cgroup_uncharge(page);
>  
>  		page->pgmap->page_free(page, page->pgmap->data);
> diff --git a/mm/hmm.c b/mm/hmm.c
> index de7b6bf77201..f9d1d89dec4d 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -963,6 +963,8 @@ static void hmm_devmem_free(struct page *page, void *data)
>  {
>  	struct hmm_devmem *devmem = data;
>  
> +	page->mapping = NULL;
> +
>  	devmem->ops->free(devmem, page);
>  }
>  
> 
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