The patch titled
Subject: mm: zswap: add zswap_never_enabled()
has been added to the -mm mm-unstable branch. Its filename is
mm-zswap-add-zswap_never_enabled.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-zswap-add-zswap_never_enabled.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Subject: mm: zswap: add zswap_never_enabled()
Date: Tue, 11 Jun 2024 02:45:15 +0000
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.
Link: https://lkml.kernel.org/r/20240611024516.1375191-2-yosryahmed@xxxxxxxxxx
Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Reviewed-by: Nhat Pham <nphamcs@xxxxxxxxx>
Cc: Barry Song <baohua@xxxxxxxxxx>
Cc: Chengming Zhou <chengming.zhou@xxxxxxxxx>
Cc: Chris Li <chrisl@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/zswap.c | 10 ++++++++++
1 file changed, 10 insertions(+)
--- a/mm/zswap.c~mm-zswap-add-zswap_never_enabled
+++ a/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;
_
Patches currently in -mm which might be from yosryahmed@xxxxxxxxxx are
mm-zswap-use-sg_set_folio-in-zswap_compress-decompress.patch
mm-zswap-use-kmap_local_folio-in-zswap_load.patch
mm-zswap-make-same_filled-functions-folio-friendly.patch
mm-rmap-abstract-updating-per-node-and-per-memcg-stats.patch
mm-swap-remove-synchronous-argument-to-swap_read_folio.patch
mm-zswap-rename-is_zswap_enabled-to-zswap_is_enabled.patch
mm-zswap-add-zswap_never_enabled.patch
mm-zswap-handle-incorrect-attempts-to-load-large-folios.patch
