RE: [PATCH 3/7] mm: factor out a swap_readpage_bdev helper

[Dan Williams <dan.j.williams@intel.com>]

Christoph Hellwig wrote:
> Split the block device case from swap_readpage into a separate helper,
> following the abstraction for file based swap and frontswap.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  mm/page_io.c | 68 +++++++++++++++++++++++++++-------------------------
>  1 file changed, 35 insertions(+), 33 deletions(-)
> 
> diff --git a/mm/page_io.c b/mm/page_io.c
> index 6f7166fdc4b2bb..ce0b3638094f85 100644
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -445,44 +445,15 @@ static void swap_readpage_fs(struct page *page,
>  		*plug = sio;
>  }
>  
> -void swap_readpage(struct page *page, bool synchronous, struct swap_iocb **plug)
> +static void swap_readpage_bdev(struct page *page, bool synchronous,
> +		struct swap_info_struct *sis)
>  {
>  	struct bio *bio;
> -	struct swap_info_struct *sis = page_swap_info(page);
> -	bool workingset = PageWorkingset(page);
> -	unsigned long pflags;
> -	bool in_thrashing;
> -
> -	VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page);
> -	VM_BUG_ON_PAGE(!PageLocked(page), page);
> -	VM_BUG_ON_PAGE(PageUptodate(page), page);
> -
> -	/*
> -	 * Count submission time as memory stall and delay. When the device
> -	 * is congested, or the submitting cgroup IO-throttled, submission
> -	 * can be a significant part of overall IO time.
> -	 */
> -	if (workingset) {
> -		delayacct_thrashing_start(&in_thrashing);
> -		psi_memstall_enter(&pflags);
> -	}
> -	delayacct_swapin_start();
> -
> -	if (frontswap_load(page) == 0) {
> -		SetPageUptodate(page);
> -		unlock_page(page);
> -		goto out;
> -	}
> -
> -	if (data_race(sis->flags & SWP_FS_OPS)) {
> -		swap_readpage_fs(page, plug);
> -		goto out;
> -	}
>  
>  	if ((sis->flags & SWP_SYNCHRONOUS_IO) &&
>  	    !bdev_read_page(sis->bdev, swap_page_sector(page), page)) {
>  		count_vm_event(PSWPIN);
> -		goto out;
> +		return;
>  	}
>  
>  	bio = bio_alloc(sis->bdev, 1, REQ_OP_READ, GFP_KERNEL);
> @@ -509,8 +480,39 @@ void swap_readpage(struct page *page, bool synchronous, struct swap_iocb **plug)
>  	}
>  	__set_current_state(TASK_RUNNING);
>  	bio_put(bio);
> +}
> +
> +void swap_readpage(struct page *page, bool synchronous, struct swap_iocb **plug)
> +{
> +	struct swap_info_struct *sis = page_swap_info(page);
> +	bool workingset = PageWorkingset(page);
> +	unsigned long pflags;
> +	bool in_thrashing;
> +
> +	VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page);
> +	VM_BUG_ON_PAGE(!PageLocked(page), page);
> +	VM_BUG_ON_PAGE(PageUptodate(page), page);
> +
> +	/*
> +	 * Count submission time as memory stall and delay. When the device
> +	 * is congested, or the submitting cgroup IO-throttled, submission
> +	 * can be a significant part of overall IO time.
> +	 */
> +	if (workingset) {
> +		delayacct_thrashing_start(&in_thrashing);
> +		psi_memstall_enter(&pflags);
> +	}
> +	delayacct_swapin_start();
> +
> +	if (frontswap_load(page) == 0) {
> +		SetPageUptodate(page);
> +		unlock_page(page);
> +	} else if (data_race(sis->flags & SWP_FS_OPS)) {
> +		swap_readpage_fs(page, plug);
> +	} else {
> +		swap_readpage_bdev(page, synchronous, sis);
> +	}
>  
> -out:
>  	if (workingset) {
>  		delayacct_thrashing_end(&in_thrashing);
>  		psi_memstall_leave(&pflags);

Looks good, passes tests,

Reviewed-by: Dan Williams <dan.j.williams@intel.com>