linux-kernel - [PATCHv8 5/8] mm: break up swap_writepage() for frontswap backends

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Date:	Thu,  4 Apr 2013 17:10:43 -0500
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Nitin Gupta <ngupta@...are.org>,
	Minchan Kim <minchan@...nel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>,
	Jenifer Hopper <jhopper@...ibm.com>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <jweiner@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Larry Woodman <lwoodman@...hat.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Joe Perches <joe@...ches.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Cody P Schafer <cody@...ux.vnet.ibm.com>,
	Hugh Dickens <hughd@...gle.com>,
	Paul Mackerras <paulus@...ba.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org
Subject: [PATCHv8 5/8] mm: break up swap_writepage() for frontswap backends

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.

__add_to_swap_cache() is also made non-static so that the page for
which writeback is to be resumed can be added to the swap cache.

Acked-by: Minchan Kim <minchan@...nel.org>
Signed-off-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>
---
 include/linux/swap.h |  2 ++
 mm/page_io.c         | 16 +++++++++++++---
 mm/swap_state.c      |  2 +-
 3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 2818a12..76f6c3b 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -330,6 +330,7 @@ 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 int __swap_writepage(struct page *page, struct writeback_control *wbc);
 extern int swap_set_page_dirty(struct page *page);
 extern void end_swap_bio_read(struct bio *bio, int err);
 
@@ -345,6 +346,7 @@ extern unsigned long total_swapcache_pages(void);
 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);
 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 78eee32..1cb382d 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -179,15 +179,15 @@ bad_bmap:
 	goto out;
 }
 
+int __swap_writepage(struct page *page, struct writeback_control *wbc);
+
 /*
  * 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);
@@ -199,6 +199,16 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
 		end_page_writeback(page);
 		goto out;
 	}
+	ret = __swap_writepage(page, wbc);
+out:
+	return ret;
+}
+
+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);
 
 	if (sis->flags & SWP_FILE) {
 		struct kiocb kiocb;
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 7efcf15..fe43fd5 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -78,7 +78,7 @@ 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)
 {
 	int error;
 	struct address_space *address_space;
-- 
1.8.2

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