Re: [PATCHv2 7/9] mm: break up swap_writepage() for frontswap backends

[Minchan Kim <minchan@kernel.org>]

On Mon, Jan 07, 2013 at 02:24:38PM -0600, Seth Jennings wrote:
> swap_writepage() is currently where frontswap hooks into the swap
> write path to capture pages with the frontswap_store() function.
> However, if a frontswap backend wants to "resume" the writeback of
> a page to the swap device, it can't call swap_writepage() as
> the page will simply reenter the backend.
> 
> This patch separates swap_writepage() into a top and bottom half, the
> bottom half named __swap_writepage() to allow a frontswap backend,
> like zswap, to resume writeback beyond the frontswap_store() hook and
> by notified when the writeback completes.
> 
> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>

Looks good to me except few nitpicks.

Acked-by: Minchan Kim <minchan@kernel.org>

> ---
>  include/linux/swap.h |    4 ++++
>  mm/page_io.c         |   22 +++++++++++++++++-----
>  mm/swap_state.c      |    2 +-
>  3 files changed, 22 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 8c66486..a3da829 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -321,6 +321,9 @@ static inline void mem_cgroup_uncharge_swap(swp_entry_t ent)
>  /* linux/mm/page_io.c */
>  extern int swap_readpage(struct page *);
>  extern int swap_writepage(struct page *page, struct writeback_control *wbc);
> +extern void end_swap_bio_write(struct bio *bio, int err);
> +extern int __swap_writepage(struct page *page, struct writeback_control *wbc,
> +	void (*end_write_func)(struct bio *, int));
>  extern int swap_set_page_dirty(struct page *page);
>  extern void end_swap_bio_read(struct bio *bio, int err);
>  
> @@ -335,6 +338,7 @@ extern struct address_space swapper_space;
>  extern void show_swap_cache_info(void);
>  extern int add_to_swap(struct page *);
>  extern int add_to_swap_cache(struct page *, swp_entry_t, gfp_t);
> +extern int __add_to_swap_cache(struct page *page, swp_entry_t entry);

What's related __add_to_swap_cache with this patch?

>  extern void __delete_from_swap_cache(struct page *);
>  extern void delete_from_swap_cache(struct page *);
>  extern void free_page_and_swap_cache(struct page *);
> diff --git a/mm/page_io.c b/mm/page_io.c
> index c535d39..806085e 100644
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -43,7 +43,7 @@ static struct bio *get_swap_bio(gfp_t gfp_flags,
>  	return bio;
>  }
>  
> -static void end_swap_bio_write(struct bio *bio, int err)
> +void end_swap_bio_write(struct bio *bio, int err)

Why do you remove static in this patch? It's not related to the patch.

>  {
>  	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
>  	struct page *page = bio->bi_io_vec[0].bv_page;
> @@ -180,15 +180,16 @@ bad_bmap:
>  	goto out;
>  }
>  
> +int __swap_writepage(struct page *page, struct writeback_control *wbc,
> +	void (*end_write_func)(struct bio *, int));
> +
>  /*
>   * We may have stale swap cache pages in memory: notice
>   * them here and get rid of the unnecessary final write.
>   */
>  int swap_writepage(struct page *page, struct writeback_control *wbc)
>  {
> -	struct bio *bio;
> -	int ret = 0, rw = WRITE;
> -	struct swap_info_struct *sis = page_swap_info(page);
> +	int ret = 0;
>  
>  	if (try_to_free_swap(page)) {
>  		unlock_page(page);
> @@ -200,6 +201,17 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
>  		end_page_writeback(page);
>  		goto out;
>  	}
> +	ret = __swap_writepage(page, wbc, end_swap_bio_write);
> +out:
> +	return ret;
> +}
> +
> +int __swap_writepage(struct page *page, struct writeback_control *wbc,
> +	void (*end_write_func)(struct bio *, int))
> +{
> +	struct bio *bio;
> +	int ret = 0, rw = WRITE;
> +	struct swap_info_struct *sis = page_swap_info(page);
>  
>  	if (sis->flags & SWP_FILE) {
>  		struct kiocb kiocb;
> @@ -227,7 +239,7 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
>  		return ret;
>  	}
>  
> -	bio = get_swap_bio(GFP_NOIO, page, end_swap_bio_write);
> +	bio = get_swap_bio(GFP_NOIO, page, end_write_func);
>  	if (bio == NULL) {
>  		set_page_dirty(page);
>  		unlock_page(page);
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index 0cb36fb..7eded9c 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -67,7 +67,7 @@ void show_swap_cache_info(void)
>   * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
>   * but sets SwapCache flag and private instead of mapping and index.
>   */
> -static int __add_to_swap_cache(struct page *page, swp_entry_t entry)
> +int __add_to_swap_cache(struct page *page, swp_entry_t entry)

Ditto

>  {
>  	int error;
>  
> -- 
> 1.7.9.5
> 
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-- 
Kind regards,
Minchan Kim

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