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 <sjenn...@linux.vnet.ibm.com>
---
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);
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)
{
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)
{
int error;
--
1.7.9.5
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