mm: zswap: support exclusive loads

Commit 71024cb4a0bf ("frontswap: remove frontswap_tmem_exclusive_gets")
removed support for exclusive loads from frontswap as it was not used. 
Bring back exclusive loads support to frontswap by adding an "exclusive"
output parameter to frontswap_ops->load.

On the zswap side, add a module parameter to enable/disable exclusive
loads, and a config option to control the boot default value.  Refactor
zswap entry invalidation in zswap_frontswap_invalidate_page() into
zswap_invalidate_entry() to reuse it in zswap_frontswap_load() if
exclusive loads are enabled.

With exclusive loads, we avoid having two copies of the same page in
memory (compressed & uncompressed) after faulting it in from zswap.  On
the other hand, if the page is to be reclaimed again without being
dirtied, it will be re-compressed.  Compression is not usually slow, and a
page that was just faulted in is less likely to be reclaimed again soon.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Yosry Ahmed <[email protected]>
Suggested-by: Yu Zhao <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Cc: Dan Streetman <[email protected]>
Cc: Domenico Cerasuolo <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Nhat Pham <[email protected]>
Cc: Seth Jennings <[email protected]>
Cc: Vitaly Wool <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
index a631bac12220..eaa0ac5f9003 100644
--- a/include/linux/frontswap.h
+++ b/include/linux/frontswap.h
@@ -10,7 +10,7 @@
 struct frontswap_ops {
 	void (*init)(unsigned); /* this swap type was just swapon'ed */
 	int (*store)(unsigned, pgoff_t, struct page *); /* store a page */
-	int (*load)(unsigned, pgoff_t, struct page *); /* load a page */
+	int (*load)(unsigned, pgoff_t, struct page *, bool *); /* load a page */
 	void (*invalidate_page)(unsigned, pgoff_t); /* page no longer needed */
 	void (*invalidate_area)(unsigned); /* swap type just swapoff'ed */
 };