Add zswap_never_enabled() to skip the xarray lookup in zswap_load() if
zswap was never enabled on the system. It is implemented using static
branches for efficiency, as enabling zswap should be a rare event. This
could shave some cycles off zswap_load() when CONFIG_ZSWAP is used but
zswap is never enabled.
However, the real motivation behind this patch is two-fold:
- Incoming large folio swapin work will need to fallback to order-0
folios if zswap was ever enabled, because any part of the folio could
be in zswap, until proper handling of large folios with zswap is
added.
- A warning and recovery attempt will be added in a following change in
case the above was not done incorrectly. Zswap will fail the read if
the folio is large and it was ever enabled.
Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
---
mm/zswap.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/mm/zswap.c b/mm/zswap.c
index a8c8dd8cfe6f5..7fcd751e847d6 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -83,6 +83,7 @@ static bool zswap_pool_reached_full;
static int zswap_setup(void);
/* Enable/disable zswap */
+static DEFINE_STATIC_KEY_MAYBE(CONFIG_ZSWAP_DEFAULT_ON, zswap_ever_enabled);
static bool zswap_enabled = IS_ENABLED(CONFIG_ZSWAP_DEFAULT_ON);
static int zswap_enabled_param_set(const char *,
const struct kernel_param *);
@@ -136,6 +137,11 @@ bool zswap_is_enabled(void)
return zswap_enabled;
}
+static bool zswap_never_enabled(void)
+{
+ return !static_branch_maybe(CONFIG_ZSWAP_DEFAULT_ON, &zswap_ever_enabled);
+}
+
/*********************************
* data structures
**********************************/
@@ -1557,6 +1563,9 @@ bool zswap_load(struct folio *folio)
VM_WARN_ON_ONCE(!folio_test_locked(folio));
+ if (zswap_never_enabled())
+ return false;
+
/*
* When reading into the swapcache, invalidate our entry. The
* swapcache can be the authoritative owner of the page and
@@ -1735,6 +1744,7 @@ static int zswap_setup(void)
zpool_get_type(pool->zpools[0]));
list_add(&pool->list, &zswap_pools);
zswap_has_pool = true;
+ static_branch_enable(&zswap_ever_enabled);
} else {
pr_err("pool creation failed\n");
zswap_enabled = false;
--
2.45.2.505.gda0bf45e8d-goog
