* [PATCH] mm: zswap: avoid unnecessary xarray lookup in zswap_store()
@ 2026-09-09 12:35 Kefeng Wang
2026-09-09 12:53 ` Kefeng Wang
2026-09-09 14:52 ` Johannes Weiner
0 siblings, 2 replies; 4+ messages in thread
From: Kefeng Wang @ 2026-09-09 12:35 UTC (permalink / raw)
To: Andrew Morton
Cc: linux-mm, Kefeng Wang, Chengming Zhou, Johannes Weiner,
Kairui Song, Nhat Pham, Yosry Ahmed
zswap_store() falls through to check_old and walks the swap xarray
even when zswap is disabled. Add a zswap_never_enabled() early return
matching zswap_load(), and reuse zswap_invalidate() whose xa_empty()
check skips empty per-area trees to avoid unnecessary xarry lockup.
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
mm/zswap.c | 16 +++++++---------
1 file changed, 7 insertions(+), 9 deletions(-)
diff --git a/mm/zswap.c b/mm/zswap.c
index 5d0d8bd72193..fc6c5e0db5e4 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1488,6 +1488,9 @@ bool zswap_store(struct folio *folio)
VM_WARN_ON_ONCE(!folio_test_locked(folio));
VM_WARN_ON_ONCE(!folio_test_swapcache(folio));
+ if (zswap_never_enabled())
+ return false;
+
if (!zswap_enabled)
goto check_old;
@@ -1545,15 +1548,10 @@ bool zswap_store(struct folio *folio)
if (!ret) {
unsigned type = swp_type(swp);
pgoff_t offset = swp_offset(swp);
- struct zswap_entry *entry;
- struct xarray *tree;
-
- for (index = 0; index < nr_pages; ++index) {
- tree = swap_zswap_tree(swp_entry(type, offset + index));
- entry = xa_erase(tree, offset + index);
- if (entry)
- zswap_entry_free(entry);
- }
+
+ for (index = 0; index < nr_pages; ++index)
+ zswap_invalidate(swp_entry(type, offset + index));
+
}
return ret;
--
2.55.0
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] mm: zswap: avoid unnecessary xarray lookup in zswap_store()
2026-09-09 12:35 [PATCH] mm: zswap: avoid unnecessary xarray lookup in zswap_store() Kefeng Wang
@ 2026-09-09 12:53 ` Kefeng Wang
2026-09-09 14:52 ` Johannes Weiner
1 sibling, 0 replies; 4+ messages in thread
From: Kefeng Wang @ 2026-09-09 12:53 UTC (permalink / raw)
To: Andrew Morton
Cc: linux-mm, Chengming Zhou, Johannes Weiner, Kairui Song, Nhat Pham,
Yosry Ahmed
On 9/9/2026 8:35 PM, Kefeng Wang wrote:
> zswap_store() falls through to check_old and walks the swap xarray
> even when zswap is disabled. Add a zswap_never_enabled() early return
> matching zswap_load(), and reuse zswap_invalidate() whose xa_empty()
> check skips empty per-area trees to avoid unnecessary xarry lockup.
Sorry for the typo, should be "xarray lookup".
>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> Cc: Chengming Zhou <chengming.zhou@linux.dev>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Kairui Song <kasong@tencent.com>
> Cc: Nhat Pham <nphamcs@gmail.com>
> Cc: Yosry Ahmed <yosryahmed@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> ---
> mm/zswap.c | 16 +++++++---------
> 1 file changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 5d0d8bd72193..fc6c5e0db5e4 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1488,6 +1488,9 @@ bool zswap_store(struct folio *folio)
> VM_WARN_ON_ONCE(!folio_test_locked(folio));
> VM_WARN_ON_ONCE(!folio_test_swapcache(folio));
>
> + if (zswap_never_enabled())
> + return false;
> +
> if (!zswap_enabled)
> goto check_old;
>
> @@ -1545,15 +1548,10 @@ bool zswap_store(struct folio *folio)
> if (!ret) {
> unsigned type = swp_type(swp);
> pgoff_t offset = swp_offset(swp);
> - struct zswap_entry *entry;
> - struct xarray *tree;
> -
> - for (index = 0; index < nr_pages; ++index) {
> - tree = swap_zswap_tree(swp_entry(type, offset + index));
> - entry = xa_erase(tree, offset + index);
> - if (entry)
> - zswap_entry_free(entry);
> - }
> +
> + for (index = 0; index < nr_pages; ++index)
> + zswap_invalidate(swp_entry(type, offset + index));
> +
> }
>
> return ret;
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] mm: zswap: avoid unnecessary xarray lookup in zswap_store()
2026-09-09 12:35 [PATCH] mm: zswap: avoid unnecessary xarray lookup in zswap_store() Kefeng Wang
2026-09-09 12:53 ` Kefeng Wang
@ 2026-09-09 14:52 ` Johannes Weiner
2026-09-10 1:16 ` Kefeng Wang
1 sibling, 1 reply; 4+ messages in thread
From: Johannes Weiner @ 2026-09-09 14:52 UTC (permalink / raw)
To: Kefeng Wang
Cc: Andrew Morton, linux-mm, Chengming Zhou, Kairui Song, Nhat Pham,
Yosry Ahmed
On Wed, Sep 09, 2026 at 08:35:47PM +0800, Kefeng Wang wrote:
> zswap_store() falls through to check_old and walks the swap xarray
> even when zswap is disabled. Add a zswap_never_enabled() early return
> matching zswap_load(), and reuse zswap_invalidate() whose xa_empty()
> check skips empty per-area trees to avoid unnecessary xarry lockup.
>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> Cc: Chengming Zhou <chengming.zhou@linux.dev>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Kairui Song <kasong@tencent.com>
> Cc: Nhat Pham <nphamcs@gmail.com>
> Cc: Yosry Ahmed <yosryahmed@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
These are really two separate changes. Can you please split them out?
> ---
> mm/zswap.c | 16 +++++++---------
> 1 file changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 5d0d8bd72193..fc6c5e0db5e4 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1488,6 +1488,9 @@ bool zswap_store(struct folio *folio)
> VM_WARN_ON_ONCE(!folio_test_locked(folio));
> VM_WARN_ON_ONCE(!folio_test_swapcache(folio));
>
> + if (zswap_never_enabled())
> + return false;
Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>
> @@ -1545,15 +1548,10 @@ bool zswap_store(struct folio *folio)
> if (!ret) {
> unsigned type = swp_type(swp);
> pgoff_t offset = swp_offset(swp);
> - struct zswap_entry *entry;
> - struct xarray *tree;
> -
> - for (index = 0; index < nr_pages; ++index) {
> - tree = swap_zswap_tree(swp_entry(type, offset + index));
> - entry = xa_erase(tree, offset + index);
> - if (entry)
> - zswap_entry_free(entry);
> - }
> +
> + for (index = 0; index < nr_pages; ++index)
> + zswap_invalidate(swp_entry(type, offset + index));
That dance through a swp_entry_t was already kind of awful. This would
be a good opportunity to refactor things to avoid that:
diff --git a/mm/zswap.c b/mm/zswap.c
index e6ec3295bdb0..df18fdaae703 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -228,10 +228,15 @@ static bool zswap_has_pool;
/* One swap address space for each 64M swap space */
#define ZSWAP_ADDRESS_SPACE_SHIFT 14
#define ZSWAP_ADDRESS_SPACE_PAGES (1 << ZSWAP_ADDRESS_SPACE_SHIFT)
+
+static inline struct xarray *zswap_tree(int type, pgoff_t offset)
+{
+ return &zswap_trees[type][offset >> ZSWAP_ADDRESS_SPACE_SHIFT];
+}
+
static inline struct xarray *swap_zswap_tree(swp_entry_t swp)
{
- return &zswap_trees[swp_type(swp)][swp_offset(swp)
- >> ZSWAP_ADDRESS_SPACE_SHIFT];
+ return zswap_tree(swp_type(swp), swp_offset(swp));
}
#define zswap_pool_debug(msg, p) \
@@ -729,6 +734,19 @@ static void zswap_entry_free(struct zswap_entry *entry)
atomic_long_dec(&zswap_stored_pages);
}
+static void __zswap_invalidate(int type, pgoff_t offset)
+{
+ struct xarray *tree = zswap_tree(type, offset);
+ struct zswap_entry *entry;
+
+ if (xa_empty(tree))
+ return;
+
+ entry = xa_erase(tree, offset);
+ if (entry)
+ zswap_entry_free(entry);
+}
+
/*********************************
* compressed storage functions
**********************************/
@@ -1554,12 +1572,8 @@ bool zswap_store(struct folio *folio)
struct zswap_entry *entry;
struct xarray *tree;
- for (index = 0; index < nr_pages; ++index) {
- tree = swap_zswap_tree(swp_entry(type, offset + index));
- entry = xa_erase(tree, offset + index);
- if (entry)
- zswap_entry_free(entry);
- }
+ for (index = 0; index < nr_pages; ++index)
+ __zswap_invalidate(type, offset + index);
}
return ret;
@@ -1647,16 +1661,7 @@ int zswap_load(struct folio *folio)
void zswap_invalidate(swp_entry_t swp)
{
- pgoff_t offset = swp_offset(swp);
- struct xarray *tree = swap_zswap_tree(swp);
- struct zswap_entry *entry;
-
- if (xa_empty(tree))
- return;
-
- entry = xa_erase(tree, offset);
- if (entry)
- zswap_entry_free(entry);
+ __zswap_invalidate(swp_type(swp), swp_offset(swp));
}
int zswap_swapon(int type, unsigned long nr_pages)
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] mm: zswap: avoid unnecessary xarray lookup in zswap_store()
2026-09-09 14:52 ` Johannes Weiner
@ 2026-09-10 1:16 ` Kefeng Wang
0 siblings, 0 replies; 4+ messages in thread
From: Kefeng Wang @ 2026-09-10 1:16 UTC (permalink / raw)
To: Johannes Weiner
Cc: Andrew Morton, linux-mm, Chengming Zhou, Kairui Song, Nhat Pham,
Yosry Ahmed
On 9/9/2026 10:52 PM, Johannes Weiner wrote:
> On Wed, Sep 09, 2026 at 08:35:47PM +0800, Kefeng Wang wrote:
>> zswap_store() falls through to check_old and walks the swap xarray
>> even when zswap is disabled. Add a zswap_never_enabled() early return
>> matching zswap_load(), and reuse zswap_invalidate() whose xa_empty()
>> check skips empty per-area trees to avoid unnecessary xarry lockup.
>>
>> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
>> Cc: Chengming Zhou <chengming.zhou@linux.dev>
>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>> Cc: Kairui Song <kasong@tencent.com>
>> Cc: Nhat Pham <nphamcs@gmail.com>
>> Cc: Yosry Ahmed <yosryahmed@google.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>
> These are really two separate changes. Can you please split them out?
Sure.
>
>> ---
>> mm/zswap.c | 16 +++++++---------
>> 1 file changed, 7 insertions(+), 9 deletions(-)
>>
>> diff --git a/mm/zswap.c b/mm/zswap.c
>> index 5d0d8bd72193..fc6c5e0db5e4 100644
>> --- a/mm/zswap.c
>> +++ b/mm/zswap.c
>> @@ -1488,6 +1488,9 @@ bool zswap_store(struct folio *folio)
>> VM_WARN_ON_ONCE(!folio_test_locked(folio));
>> VM_WARN_ON_ONCE(!folio_test_swapcache(folio));
>>
>> + if (zswap_never_enabled())
>> + return false;
>
> Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>
>
Thanks.
>> @@ -1545,15 +1548,10 @@ bool zswap_store(struct folio *folio)
>> if (!ret) {
>> unsigned type = swp_type(swp);
>> pgoff_t offset = swp_offset(swp);
>> - struct zswap_entry *entry;
>> - struct xarray *tree;
>> -
>> - for (index = 0; index < nr_pages; ++index) {
>> - tree = swap_zswap_tree(swp_entry(type, offset + index));
>> - entry = xa_erase(tree, offset + index);
>> - if (entry)
>> - zswap_entry_free(entry);
>> - }
>> +
>> + for (index = 0; index < nr_pages; ++index)
>> + zswap_invalidate(swp_entry(type, offset + index));
>
> That dance through a swp_entry_t was already kind of awful. This would
> be a good opportunity to refactor things to avoid that:
It looks better, thanks for your review. will update.
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index e6ec3295bdb0..df18fdaae703 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -228,10 +228,15 @@ static bool zswap_has_pool;
> /* One swap address space for each 64M swap space */
> #define ZSWAP_ADDRESS_SPACE_SHIFT 14
> #define ZSWAP_ADDRESS_SPACE_PAGES (1 << ZSWAP_ADDRESS_SPACE_SHIFT)
> +
> +static inline struct xarray *zswap_tree(int type, pgoff_t offset)
> +{
> + return &zswap_trees[type][offset >> ZSWAP_ADDRESS_SPACE_SHIFT];
> +}
> +
> static inline struct xarray *swap_zswap_tree(swp_entry_t swp)
> {
> - return &zswap_trees[swp_type(swp)][swp_offset(swp)
> - >> ZSWAP_ADDRESS_SPACE_SHIFT];
> + return zswap_tree(swp_type(swp), swp_offset(swp));
> }
>
> #define zswap_pool_debug(msg, p) \
> @@ -729,6 +734,19 @@ static void zswap_entry_free(struct zswap_entry *entry)
> atomic_long_dec(&zswap_stored_pages);
> }
>
> +static void __zswap_invalidate(int type, pgoff_t offset)
> +{
> + struct xarray *tree = zswap_tree(type, offset);
> + struct zswap_entry *entry;
> +
> + if (xa_empty(tree))
> + return;
> +
> + entry = xa_erase(tree, offset);
> + if (entry)
> + zswap_entry_free(entry);
> +}
> +
> /*********************************
> * compressed storage functions
> **********************************/
> @@ -1554,12 +1572,8 @@ bool zswap_store(struct folio *folio)
> struct zswap_entry *entry;
> struct xarray *tree;
>
> - for (index = 0; index < nr_pages; ++index) {
> - tree = swap_zswap_tree(swp_entry(type, offset + index));
> - entry = xa_erase(tree, offset + index);
> - if (entry)
> - zswap_entry_free(entry);
> - }
> + for (index = 0; index < nr_pages; ++index)
> + __zswap_invalidate(type, offset + index);
> }
>
> return ret;
> @@ -1647,16 +1661,7 @@ int zswap_load(struct folio *folio)
>
> void zswap_invalidate(swp_entry_t swp)
> {
> - pgoff_t offset = swp_offset(swp);
> - struct xarray *tree = swap_zswap_tree(swp);
> - struct zswap_entry *entry;
> -
> - if (xa_empty(tree))
> - return;
> -
> - entry = xa_erase(tree, offset);
> - if (entry)
> - zswap_entry_free(entry);
> + __zswap_invalidate(swp_type(swp), swp_offset(swp));
> }
>
> int zswap_swapon(int type, unsigned long nr_pages)
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2026-09-10 1:16 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
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2026-09-09 12:35 [PATCH] mm: zswap: avoid unnecessary xarray lookup in zswap_store() Kefeng Wang
2026-09-09 12:53 ` Kefeng Wang
2026-09-09 14:52 ` Johannes Weiner
2026-09-10 1:16 ` Kefeng Wang
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