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

[Minchan Kim]

On Mon, Jan 28, 2013 at 11:26:43AM -0600, Seth Jennings wrote:
> On 01/27/2013 10:22 PM, Minchan Kim wrote:
> > 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@xxxxxxxxxxxxxxxxxx>
> > 
> > Looks good to me except few nitpicks.
> 
> I broke these changes out from the main zswap patch (patch 8/9) in
> response to a request for Dan.  You are right in that there are
> changes here unrelated to the commit message.
> 
> The other changes are related to allowing zswap to do accounting on
> the number of outstanding flushes to the swap device.
> 
> If I'm going to break those out though the two resulting patches would be:
> 1. breakup __swap_writepage() and un-static __add_to_swap_cache() to
> allow resuming of swap page writeback
> 2. change __swap_writepage() signature to include end_write_func and
> un-static end_swap_bio_write() for accounting of outstanding flushes
> 

Or please add comment why you want to export some functions.

Thanks!

> Is that what you'd like to see?
> 
> Seth
> 
> > 
> > Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
> > 
> >> ---
> >>  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
> >>
> >> --
> >> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> >> the body to majordomo@xxxxxxxxxx  For more info on Linux MM,
> >> see: http://www.linux-mm.org/ .
> >> Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
> > 
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@xxxxxxxxxx  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>

-- 
Kind regards,
Minchan Kim
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/