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.
Suggested-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
---
v1 -> v2:
- Add a module parameter to control whether exclusive loads are enabled
or not, the config option now controls the default boot value instead.
Replaced frontswap_ops->exclusive_loads by an output parameter to
frontswap_ops->load() (Johannes Weiner).
---
include/linux/frontswap.h | 2 +-
mm/Kconfig | 16 ++++++++++++++++
mm/frontswap.c | 10 ++++++++--
mm/zswap.c | 28 ++++++++++++++++++++--------
4 files changed, 45 insertions(+), 11 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 */
};
diff --git a/mm/Kconfig b/mm/Kconfig
index 7672a22647b4..12f32f8d26bf 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -46,6 +46,22 @@ config ZSWAP_DEFAULT_ON
The selection made here can be overridden by using the kernel
command line 'zswap.enabled=' option.
+config ZSWAP_EXCLUSIVE_LOADS_DEFAULT_ON
+ bool "Invalidate zswap entries when pages are loaded"
+ depends on ZSWAP
+ help
+ If selected, exclusive loads for zswap will be enabled at boot,
+ otherwise it will be disabled.
+
+ If exclusive loads are enabled, when a page is loaded from zswap,
+ the zswap entry is invalidated at once, as opposed to leaving it
+ in zswap until the swap entry is freed.
+
+ This avoids having two copies of the same page in memory
+ (compressed and uncompressed) after faulting in a page from zswap.
+ The cost is that if the page was never dirtied and needs to be
+ swapped out again, it will be re-compressed.
+
choice
prompt "Default compressor"
depends on ZSWAP
diff --git a/mm/frontswap.c b/mm/frontswap.c
index 279e55b4ed87..2fb5df3384b8 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -206,6 +206,7 @@ int __frontswap_load(struct page *page)
int type = swp_type(entry);
struct swap_info_struct *sis = swap_info[type];
pgoff_t offset = swp_offset(entry);
+ bool exclusive = false;
VM_BUG_ON(!frontswap_ops);
VM_BUG_ON(!PageLocked(page));
@@ -215,9 +216,14 @@ int __frontswap_load(struct page *page)
return -1;
/* Try loading from each implementation, until one succeeds. */
- ret = frontswap_ops->load(type, offset, page);
- if (ret == 0)
+ ret = frontswap_ops->load(type, offset, page, &exclusive);
+ if (ret == 0) {
inc_frontswap_loads();
+ if (exclusive) {
+ SetPageDirty(page);
+ __frontswap_clear(sis, offset);
+ }
+ }
return ret;
}
diff --git a/mm/zswap.c b/mm/zswap.c
index 59da2a415fbb..bfbcedce9c89 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -137,6 +137,10 @@ static bool zswap_non_same_filled_pages_enabled = true;
module_param_named(non_same_filled_pages_enabled, zswap_non_same_filled_pages_enabled,
bool, 0644);
+static bool zswap_exclusive_loads_enabled = IS_ENABLED(
+ CONFIG_ZSWAP_EXCLUSIVE_LOADS_DEFAULT_ON);
+module_param_named(exclusive_loads, zswap_exclusive_loads_enabled, bool, 0644);
+
/*********************************
* data structures
**********************************/
@@ -1329,12 +1333,22 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
goto reject;
}
+static void zswap_invalidate_entry(struct zswap_tree *tree,
+ struct zswap_entry *entry)
+{
+ /* remove from rbtree */
+ zswap_rb_erase(&tree->rbroot, entry);
+
+ /* drop the initial reference from entry creation */
+ zswap_entry_put(tree, entry);
+}
+
/*
* returns 0 if the page was successfully decompressed
* return -1 on entry not found or error
*/
static int zswap_frontswap_load(unsigned type, pgoff_t offset,
- struct page *page)
+ struct page *page, bool *exclusive)
{
struct zswap_tree *tree = zswap_trees[type];
struct zswap_entry *entry;
@@ -1404,6 +1418,10 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
freeentry:
spin_lock(&tree->lock);
zswap_entry_put(tree, entry);
+ if (!ret && zswap_exclusive_loads_enabled) {
+ zswap_invalidate_entry(tree, entry);
+ *exclusive = true;
+ }
spin_unlock(&tree->lock);
return ret;
@@ -1423,13 +1441,7 @@ static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset)
spin_unlock(&tree->lock);
return;
}
-
- /* remove from rbtree */
- zswap_rb_erase(&tree->rbroot, entry);
-
- /* drop the initial reference from entry creation */
- zswap_entry_put(tree, entry);
-
+ zswap_invalidate_entry(tree, entry);
spin_unlock(&tree->lock);
}
--
2.41.0.162.gfafddb0af9-goog
