Re: [PATCH mm-unstable 0/5] Switch zswap to object read/write APIs

Re: [PATCH mm-unstable 0/5] Switch zswap to object read/write APIs

[Sergey Senozhatsky]

On (25/03/05 06:11), Yosry Ahmed wrote:
> This patch series updates zswap to use the new object read/write APIs
> defined by zsmalloc in [1], and remove the old object mapping APIs and
> the related code from zpool and zsmalloc.

Thank you for working on this!

Re: [PATCH mm-unstable 1/5] mm: zpool: Add interfaces for object read/write APIs

[Sergey Senozhatsky]

On (25/03/05 06:11), Yosry Ahmed wrote:
> Zsmalloc introduce new APIs to read/write objects besides mapping them.
> Add the necessary zpool interfaces.
> 
> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>

Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>

Re: [PATCH mm-unstable 1/5] mm: zpool: Add interfaces for object read/write APIs

[Johannes Weiner]

On Wed, Mar 05, 2025 at 06:11:29AM +0000, Yosry Ahmed wrote:
> Zsmalloc introduce new APIs to read/write objects besides mapping them.
> Add the necessary zpool interfaces.
> 
> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Re: [PATCH mm-unstable 1/5] mm: zpool: Add interfaces for object read/write APIs

[Nhat Pham]

On Tue, Mar 4, 2025 at 10:11 PM Yosry Ahmed <yosry.ahmed@linux.dev> wrote:
>
> Zsmalloc introduce new APIs to read/write objects besides mapping them.
> Add the necessary zpool interfaces.
>
> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>

Acked-by: Nhat Pham <nphamcs@gmail.com>

Re: [PATCH mm-unstable 2/5] mm: zswap: Use object read/write APIs instead of object mapping APIs

[Johannes Weiner]

On Wed, Mar 05, 2025 at 06:11:30AM +0000, Yosry Ahmed wrote:
> Use the new object read/write APIs instead of mapping APIs.
> 
> On compress side, zpool_obj_write() is more concise and provides exactly
> what zswap needs to write the compressed object to the zpool, instead of
> map->copy->unmap.
> 
> On the decompress side, zpool_obj_read_begin() is sleepable, which
> allows avoiding the memcpy() for zsmalloc and slightly simplifying the
> code by:
> - Avoiding checking if the zpool driver is sleepable, reducing special
>   cases and shrinking the huge comment.
> - Having a single zpool_obj_read_end() call rather than multiple
>   conditional zpool_unmap_handle() calls.
> 
> The !virt_addr_valid() case can be removed in the future if the crypto
> API supports kmap addresses or by using kmap_to_page(), completely
> eliminating the memcpy() path in zswap_decompress(). This a step toward
> that. In that spirit, opportunistically make the comment more specific
> about the kmap case instead of generic non-linear addresses. This is the
> only case that needs to be handled in practice, and the generic comment
> makes it seem like a bigger problem that it actually is.
> 
> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Re: [PATCH mm-unstable 2/5] mm: zswap: Use object read/write APIs instead of object mapping APIs

[Nhat Pham]

On Tue, Mar 4, 2025 at 10:11 PM Yosry Ahmed <yosry.ahmed@linux.dev> wrote:
>
> Use the new object read/write APIs instead of mapping APIs.
>
> On compress side, zpool_obj_write() is more concise and provides exactly
> what zswap needs to write the compressed object to the zpool, instead of
> map->copy->unmap.
>
> On the decompress side, zpool_obj_read_begin() is sleepable, which
> allows avoiding the memcpy() for zsmalloc and slightly simplifying the
> code by:
> - Avoiding checking if the zpool driver is sleepable, reducing special
>   cases and shrinking the huge comment.
> - Having a single zpool_obj_read_end() call rather than multiple
>   conditional zpool_unmap_handle() calls.
>
> The !virt_addr_valid() case can be removed in the future if the crypto
> API supports kmap addresses or by using kmap_to_page(), completely
> eliminating the memcpy() path in zswap_decompress(). This a step toward
> that. In that spirit, opportunistically make the comment more specific
> about the kmap case instead of generic non-linear addresses. This is the
> only case that needs to be handled in practice, and the generic comment
> makes it seem like a bigger problem that it actually is.
>
> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>

Acked-by: Nhat Pham <nphamcs@gmail.com>

Re: [PATCH mm-unstable 3/5] mm: zpool: Remove object mapping APIs

[Sergey Senozhatsky]

On (25/03/05 06:11), Yosry Ahmed wrote:
> zpool_map_handle(), zpool_unmap_handle(), and zpool_can_sleep_mapped()
> are no longer used. Remove them with the underlying driver callbacks.
> 
> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>

Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>

Re: [PATCH mm-unstable 3/5] mm: zpool: Remove object mapping APIs

[Johannes Weiner]

On Wed, Mar 05, 2025 at 06:11:31AM +0000, Yosry Ahmed wrote:
> zpool_map_handle(), zpool_unmap_handle(), and zpool_can_sleep_mapped()
> are no longer used. Remove them with the underlying driver callbacks.
> 
> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Re: [PATCH mm-unstable 3/5] mm: zpool: Remove object mapping APIs

[Nhat Pham]

On Tue, Mar 4, 2025 at 10:11 PM Yosry Ahmed <yosry.ahmed@linux.dev> wrote:
>
> zpool_map_handle(), zpool_unmap_handle(), and zpool_can_sleep_mapped()
> are no longer used. Remove them with the underlying driver callbacks.
>
> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
> ---
>  include/linux/zpool.h | 30 ---------------------
>  mm/zpool.c            | 61 -------------------------------------------
>  mm/zsmalloc.c         | 27 -------------------
>  3 files changed, 118 deletions(-)

Me see deletions, me likey. I've never liked the object mapping API anyway.

Acked-by: Nhat Pham <nphamcs@gmail.com>

Re: [PATCH mm-unstable 3/5] mm: zpool: Remove object mapping APIs

[Herbert Xu]

On Wed, Mar 05, 2025 at 06:11:31AM +0000, Yosry Ahmed wrote:
> zpool_map_handle(), zpool_unmap_handle(), and zpool_can_sleep_mapped()
> are no longer used. Remove them with the underlying driver callbacks.
> 
> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
> ---
>  include/linux/zpool.h | 30 ---------------------
>  mm/zpool.c            | 61 -------------------------------------------
>  mm/zsmalloc.c         | 27 -------------------
>  3 files changed, 118 deletions(-)

This patch breaks zbud and z3fold because they haven't been converted
to the new interface.

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Re: [PATCH mm-unstable 3/5] mm: zpool: Remove object mapping APIs

[Herbert Xu]

On Thu, Mar 06, 2025 at 09:48:58AM +0800, Herbert Xu wrote:
>
> This patch breaks zbud and z3fold because they haven't been converted
> to the new interface.

I've rebased my zswap SG patch on top of your series.  I've removed
all the mapping code from zpool/zsmalloc and pushed it out to zram
instead.

This patch depends on a new memcpy_sglist function which I've just
posted a patch for:

https://patchwork.kernel.org/project/linux-crypto/patch/Z8kXhLb681E_FLzs@gondor.apana.org.au/

From a77ee529b831e7e606ed2a5b723b74ce234a3915 Mon Sep 17 00:00:00 2001
From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Thu, 6 Mar 2025 12:13:58 +0800
Subject: [PATCH] mm: zswap: Give non-linear objects to Crypto API

Instead of copying non-linear objects into a buffer, use the
scatterlist to give them directly to the Crypto API.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
---
 drivers/block/zram/zram_drv.c |  58 ++++++++++++----
 include/linux/zpool.h         |  26 +++----
 include/linux/zsmalloc.h      |  11 ++-
 mm/z3fold.c                   |  17 +++--
 mm/zbud.c                     |  45 +++++++------
 mm/zpool.c                    |  54 ++++++---------
 mm/zsmalloc.c                 | 123 +++++++---------------------------
 mm/zswap.c                    |  35 +++-------
 8 files changed, 148 insertions(+), 221 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index fda7d8624889..d72becec534d 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -15,6 +15,7 @@
 #define KMSG_COMPONENT "zram"
 #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
 
+#include <crypto/scatterwalk.h>
 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/bio.h>
@@ -23,6 +24,7 @@
 #include <linux/buffer_head.h>
 #include <linux/device.h>
 #include <linux/highmem.h>
+#include <linux/scatterlist.h>
 #include <linux/slab.h>
 #include <linux/backing-dev.h>
 #include <linux/string.h>
@@ -1559,21 +1561,23 @@ static int read_same_filled_page(struct zram *zram, struct page *page,
 static int read_incompressible_page(struct zram *zram, struct page *page,
 				    u32 index)
 {
+	struct scatterlist output[1];
+	struct scatterlist input[2];
 	unsigned long handle;
-	void *src, *dst;
 
+	sg_init_table(output, 1);
+	sg_set_page(output, page, PAGE_SIZE, 0);
 	handle = zram_get_handle(zram, index);
-	src = zs_obj_read_begin(zram->mem_pool, handle, NULL);
-	dst = kmap_local_page(page);
-	copy_page(dst, src);
-	kunmap_local(dst);
-	zs_obj_read_end(zram->mem_pool, handle, src);
+	zs_pin_object(zram->mem_pool, handle, input);
+	memcpy_sglist(output, input, PAGE_SIZE);
+	zs_unpin_object(zram->mem_pool, handle);
 
 	return 0;
 }
 
 static int read_compressed_page(struct zram *zram, struct page *page, u32 index)
 {
+	struct scatterlist input[2];
 	struct zcomp_strm *zstrm;
 	unsigned long handle;
 	unsigned int size;
@@ -1585,11 +1589,22 @@ static int read_compressed_page(struct zram *zram, struct page *page, u32 index)
 	prio = zram_get_priority(zram, index);
 
 	zstrm = zcomp_stream_get(zram->comps[prio]);
-	src = zs_obj_read_begin(zram->mem_pool, handle, zstrm->local_copy);
+	zs_pin_object(zram->mem_pool, handle, input);
+	if (sg_is_last(input)) {
+		unsigned int offset = input[0].offset;
+
+		src = kmap_local_page(sg_page(input) + (offset >> PAGE_SHIFT));
+		src += offset_in_page(offset);
+	} else {
+		memcpy_from_sglist(zstrm->local_copy, input, 0, size);
+		src = zstrm->local_copy;
+	}
 	dst = kmap_local_page(page);
 	ret = zcomp_decompress(zram->comps[prio], zstrm, src, size, dst);
 	kunmap_local(dst);
-	zs_obj_read_end(zram->mem_pool, handle, src);
+	if (sg_is_last(input))
+		kunmap_local(src);
+	zs_unpin_object(zram->mem_pool, handle);
 	zcomp_stream_put(zstrm);
 
 	return ret;
@@ -1684,8 +1699,9 @@ static int write_same_filled_page(struct zram *zram, unsigned long fill,
 static int write_incompressible_page(struct zram *zram, struct page *page,
 				     u32 index)
 {
+	struct scatterlist output[2];
+	struct scatterlist input[1];
 	unsigned long handle;
-	void *src;
 
 	/*
 	 * This function is called from preemptible context so we don't need
@@ -1703,9 +1719,11 @@ static int write_incompressible_page(struct zram *zram, struct page *page,
 		return -ENOMEM;
 	}
 
-	src = kmap_local_page(page);
-	zs_obj_write(zram->mem_pool, handle, src, PAGE_SIZE);
-	kunmap_local(src);
+	sg_init_table(input, 1);
+	sg_set_page(input, page, PAGE_SIZE, 0);
+	zs_pin_object(zram->mem_pool, handle, output);
+	memcpy_sglist(output, input, PAGE_SIZE);
+	zs_unpin_object(zram->mem_pool, handle);
 
 	zram_slot_lock(zram, index);
 	zram_set_flag(zram, index, ZRAM_HUGE);
@@ -1723,6 +1741,8 @@ static int write_incompressible_page(struct zram *zram, struct page *page,
 
 static int zram_write_page(struct zram *zram, struct page *page, u32 index)
 {
+	struct scatterlist output[2];
+	struct scatterlist input[1];
 	int ret = 0;
 	unsigned long handle;
 	unsigned int comp_len;
@@ -1773,7 +1793,11 @@ static int zram_write_page(struct zram *zram, struct page *page, u32 index)
 		return -ENOMEM;
 	}
 
-	zs_obj_write(zram->mem_pool, handle, zstrm->buffer, comp_len);
+	sg_init_table(input, 1);
+	sg_set_buf(input, zstrm->buffer, comp_len);
+	zs_pin_object(zram->mem_pool, handle, output);
+	memcpy_sglist(output, input, comp_len);
+	zs_unpin_object(zram->mem_pool, handle);
 	zcomp_stream_put(zstrm);
 
 	zram_slot_lock(zram, index);
@@ -1872,6 +1896,8 @@ static int recompress_slot(struct zram *zram, u32 index, struct page *page,
 			   u64 *num_recomp_pages, u32 threshold, u32 prio,
 			   u32 prio_max)
 {
+	struct scatterlist output[2];
+	struct scatterlist input[1];
 	struct zcomp_strm *zstrm = NULL;
 	unsigned long handle_old;
 	unsigned long handle_new;
@@ -1990,7 +2016,11 @@ static int recompress_slot(struct zram *zram, u32 index, struct page *page,
 		return PTR_ERR((void *)handle_new);
 	}
 
-	zs_obj_write(zram->mem_pool, handle_new, zstrm->buffer, comp_len_new);
+	sg_init_table(input, 1);
+	sg_set_buf(input, zstrm->buffer, comp_len_new);
+	zs_pin_object(zram->mem_pool, handle_new, output);
+	memcpy_sglist(output, input, comp_len_new);
+	zs_unpin_object(zram->mem_pool, handle_new);
 	zcomp_stream_put(zstrm);
 
 	zram_free_page(zram, index);
diff --git a/include/linux/zpool.h b/include/linux/zpool.h
index a976f1962cc7..2beb0b7c82e2 100644
--- a/include/linux/zpool.h
+++ b/include/linux/zpool.h
@@ -12,6 +12,7 @@
 #ifndef _ZPOOL_H_
 #define _ZPOOL_H_
 
+struct scatterlist;
 struct zpool;
 
 bool zpool_has_pool(char *type);
@@ -27,14 +28,10 @@ int zpool_malloc(struct zpool *pool, size_t size, gfp_t gfp,
 
 void zpool_free(struct zpool *pool, unsigned long handle);
 
-void *zpool_obj_read_begin(struct zpool *zpool, unsigned long handle,
-			   void *local_copy);
+void zpool_pin_handle(struct zpool *pool, unsigned long handle,
+		      struct scatterlist *sg);
 
-void zpool_obj_read_end(struct zpool *zpool, unsigned long handle,
-			void *handle_mem);
-
-void zpool_obj_write(struct zpool *zpool, unsigned long handle,
-		     void *handle_mem, size_t mem_len);
+void zpool_unpin_handle(struct zpool *pool, unsigned long handle);
 
 u64 zpool_get_total_pages(struct zpool *pool);
 
@@ -47,9 +44,8 @@ u64 zpool_get_total_pages(struct zpool *pool);
  * @destroy:	destroy a pool.
  * @malloc:	allocate mem from a pool.
  * @free:	free mem from a pool.
- * @sleep_mapped: whether zpool driver can sleep during map.
- * @map:	map a handle.
- * @unmap:	unmap a handle.
+ * @pin:	pin a handle and write it into a two-entry SG list.
+ * @unpin:	unpin a handle.
  * @total_size:	get total size of a pool.
  *
  * This is created by a zpool implementation and registered
@@ -68,12 +64,8 @@ struct zpool_driver {
 				unsigned long *handle);
 	void (*free)(void *pool, unsigned long handle);
 
-	void *(*obj_read_begin)(void *pool, unsigned long handle,
-				void *local_copy);
-	void (*obj_read_end)(void *pool, unsigned long handle,
-			     void *handle_mem);
-	void (*obj_write)(void *pool, unsigned long handle,
-			  void *handle_mem, size_t mem_len);
+	void (*pin)(void *pool, unsigned long handle, struct scatterlist *sg);
+	void (*unpin)(void *pool, unsigned long handle);
 
 	u64 (*total_pages)(void *pool);
 };
@@ -82,6 +74,4 @@ void zpool_register_driver(struct zpool_driver *driver);
 
 int zpool_unregister_driver(struct zpool_driver *driver);
 
-bool zpool_can_sleep_mapped(struct zpool *pool);
-
 #endif
diff --git a/include/linux/zsmalloc.h b/include/linux/zsmalloc.h
index c26baf9fb331..fba57a792153 100644
--- a/include/linux/zsmalloc.h
+++ b/include/linux/zsmalloc.h
@@ -16,6 +16,8 @@
 
 #include <linux/types.h>
 
+struct scatterlist;
+
 struct zs_pool_stats {
 	/* How many pages were migrated (freed) */
 	atomic_long_t pages_compacted;
@@ -38,11 +40,8 @@ unsigned int zs_lookup_class_index(struct zs_pool *pool, unsigned int size);
 
 void zs_pool_stats(struct zs_pool *pool, struct zs_pool_stats *stats);
 
-void *zs_obj_read_begin(struct zs_pool *pool, unsigned long handle,
-			void *local_copy);
-void zs_obj_read_end(struct zs_pool *pool, unsigned long handle,
-		     void *handle_mem);
-void zs_obj_write(struct zs_pool *pool, unsigned long handle,
-		  void *handle_mem, size_t mem_len);
+void zs_pin_object(struct zs_pool *pool, unsigned long handle,
+		   struct scatterlist *sg);
+void zs_unpin_object(struct zs_pool *pool, unsigned long handle);
 
 #endif
diff --git a/mm/z3fold.c b/mm/z3fold.c
index 379d24b4fef9..eab5c81fa7ad 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -36,6 +36,7 @@
 #include <linux/percpu.h>
 #include <linux/preempt.h>
 #include <linux/workqueue.h>
+#include <linux/scatterlist.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/zpool.h>
@@ -1392,12 +1393,15 @@ static void z3fold_zpool_free(void *pool, unsigned long handle)
 	z3fold_free(pool, handle);
 }
 
-static void *z3fold_zpool_map(void *pool, unsigned long handle,
-			enum zpool_mapmode mm)
+static void z3fold_zpool_pin(void *pool, unsigned long handle,
+			     struct scatterlist sg[2])
 {
-	return z3fold_map(pool, handle);
+	void *buf = z3fold_map(pool, handle);
+
+	sg_init_one(sg, buf, PAGE_SIZE - offset_in_page(buf));
 }
-static void z3fold_zpool_unmap(void *pool, unsigned long handle)
+
+static void z3fold_zpool_unpin(void *pool, unsigned long handle)
 {
 	z3fold_unmap(pool, handle);
 }
@@ -1409,14 +1413,13 @@ static u64 z3fold_zpool_total_pages(void *pool)
 
 static struct zpool_driver z3fold_zpool_driver = {
 	.type =		"z3fold",
-	.sleep_mapped = true,
 	.owner =	THIS_MODULE,
 	.create =	z3fold_zpool_create,
 	.destroy =	z3fold_zpool_destroy,
 	.malloc =	z3fold_zpool_malloc,
 	.free =		z3fold_zpool_free,
-	.map =		z3fold_zpool_map,
-	.unmap =	z3fold_zpool_unmap,
+	.pin =		z3fold_zpool_pin,
+	.unpin =	z3fold_zpool_unpin,
 	.total_pages =	z3fold_zpool_total_pages,
 };
 
diff --git a/mm/zbud.c b/mm/zbud.c
index e9836fff9438..3132a7c6f926 100644
--- a/mm/zbud.c
+++ b/mm/zbud.c
@@ -36,10 +36,9 @@
  *
  * The zbud API differs from that of conventional allocators in that the
  * allocation function, zbud_alloc(), returns an opaque handle to the user,
- * not a dereferenceable pointer.  The user must map the handle using
- * zbud_map() in order to get a usable pointer by which to access the
- * allocation data and unmap the handle with zbud_unmap() when operations
- * on the allocation data are complete.
+ * not a dereferenceable pointer.  The user must pin the handle using
+ * zbud_pin() in order to access the allocation data and unpin the handle
+ * with zbud_unpin() when operations on the allocation data are complete.
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
@@ -49,6 +48,7 @@
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/preempt.h>
+#include <linux/scatterlist.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/zpool.h>
@@ -339,28 +339,30 @@ static void zbud_free(struct zbud_pool *pool, unsigned long handle)
 }
 
 /**
- * zbud_map() - maps the allocation associated with the given handle
+ * zbud_pin() - pins the allocation associated with the given handle
  * @pool:	pool in which the allocation resides
- * @handle:	handle associated with the allocation to be mapped
+ * @handle:	handle associated with the allocation to be pinned
+ * @sg:		2-entry scatter list to store the memory pointers
  *
- * While trivial for zbud, the mapping functions for others allocators
+ * While trivial for zbud, the pinning functions for others allocators
  * implementing this allocation API could have more complex information encoded
  * in the handle and could create temporary mappings to make the data
  * accessible to the user.
- *
- * Returns: a pointer to the mapped allocation
  */
-static void *zbud_map(struct zbud_pool *pool, unsigned long handle)
+static void zbud_pin(struct zbud_pool *pool, unsigned long handle,
+		      struct scatterlist sg[2])
 {
-	return (void *)(handle);
+	void *buf = (void *)handle;
+
+	sg_init_one(sg, buf, PAGE_SIZE - offset_in_page(buf));
 }
 
 /**
- * zbud_unmap() - maps the allocation associated with the given handle
+ * zbud_unpin() - unpins the allocation associated with the given handle
  * @pool:	pool in which the allocation resides
- * @handle:	handle associated with the allocation to be unmapped
+ * @handle:	handle associated with the allocation to be unpinned
  */
-static void zbud_unmap(struct zbud_pool *pool, unsigned long handle)
+static void zbud_unpin(struct zbud_pool *pool, unsigned long handle)
 {
 }
 
@@ -400,14 +402,14 @@ static void zbud_zpool_free(void *pool, unsigned long handle)
 	zbud_free(pool, handle);
 }
 
-static void *zbud_zpool_map(void *pool, unsigned long handle,
-			enum zpool_mapmode mm)
+static void zbud_zpool_pin(void *pool, unsigned long handle,
+			   struct scatterlist sg[2])
 {
-	return zbud_map(pool, handle);
+	zbud_pin(pool, handle, sg);
 }
-static void zbud_zpool_unmap(void *pool, unsigned long handle)
+static void zbud_zpool_unpin(void *pool, unsigned long handle)
 {
-	zbud_unmap(pool, handle);
+	zbud_unpin(pool, handle);
 }
 
 static u64 zbud_zpool_total_pages(void *pool)
@@ -417,14 +419,13 @@ static u64 zbud_zpool_total_pages(void *pool)
 
 static struct zpool_driver zbud_zpool_driver = {
 	.type =		"zbud",
-	.sleep_mapped = true,
 	.owner =	THIS_MODULE,
 	.create =	zbud_zpool_create,
 	.destroy =	zbud_zpool_destroy,
 	.malloc =	zbud_zpool_malloc,
 	.free =		zbud_zpool_free,
-	.map =		zbud_zpool_map,
-	.unmap =	zbud_zpool_unmap,
+	.pin =		zbud_zpool_pin,
+	.unpin =	zbud_zpool_unpin,
 	.total_pages =	zbud_zpool_total_pages,
 };
 
diff --git a/mm/zpool.c b/mm/zpool.c
index 0931b8135d72..3355b57ec7ee 100644
--- a/mm/zpool.c
+++ b/mm/zpool.c
@@ -13,6 +13,7 @@
 #include <linux/list.h>
 #include <linux/types.h>
 #include <linux/mm.h>
+#include <linux/scatterlist.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/module.h>
@@ -262,51 +263,38 @@ void zpool_free(struct zpool *zpool, unsigned long handle)
 }
 
 /**
- * zpool_obj_read_begin() - Start reading from a previously allocated handle.
+ * zpool_pin_handle() - Pin a previously allocated handle into memory
  * @zpool:	The zpool that the handle was allocated from
- * @handle:	The handle to read from
- * @local_copy:	A local buffer to use if needed.
+ * @handle:	The handle to pin
+ * @sg:		2-entry scatterlist to store pointers to the memmory
  *
- * This starts a read operation of a previously allocated handle. The passed
- * @local_copy buffer may be used if needed by copying the memory into.
- * zpool_obj_read_end() MUST be called after the read is completed to undo any
- * actions taken (e.g. release locks).
+ * This pins a previously allocated handle into memory.
  *
- * Returns: A pointer to the handle memory to be read, if @local_copy is used,
- * the returned pointer is @local_copy.
+ * This may hold locks, disable interrupts, and/or preemption,
+ * and the zpool_unpin_handle() must be called to undo those
+ * actions.  The code that uses the pinned handle should complete
+ * its operations on the pinned handle memory quickly and unpin
+ * as soon as possible.
  */
-void *zpool_obj_read_begin(struct zpool *zpool, unsigned long handle,
-			   void *local_copy)
+void zpool_pin_handle(struct zpool *zpool, unsigned long handle,
+		      struct scatterlist *sg)
 {
-	return zpool->driver->obj_read_begin(zpool->pool, handle, local_copy);
+	zpool->driver->pin(zpool->pool, handle, sg);
 }
 
 /**
- * zpool_obj_read_end() - Finish reading from a previously allocated handle.
+ * zpool_unpin_handle() - Unpin a previously pinned handle
  * @zpool:	The zpool that the handle was allocated from
- * @handle:	The handle to read from
- * @handle_mem:	The pointer returned by zpool_obj_read_begin()
+ * @handle:	The handle to unpin
  *
- * Finishes a read operation previously started by zpool_obj_read_begin().
+ * This unpins a previously pinned handle.  Any locks or other
+ * actions that the implementation took in zpool_pin_handle()
+ * will be undone here.  The memory area returned from
+ * zpool_pin_handle() should no longer be used after this.
  */
-void zpool_obj_read_end(struct zpool *zpool, unsigned long handle,
-			void *handle_mem)
+void zpool_unpin_handle(struct zpool *zpool, unsigned long handle)
 {
-	zpool->driver->obj_read_end(zpool->pool, handle, handle_mem);
-}
-
-/**
- * zpool_obj_write() - Write to a previously allocated handle.
- * @zpool:	The zpool that the handle was allocated from
- * @handle:	The handle to read from
- * @handle_mem:	The memory to copy from into the handle.
- * @mem_len:	The length of memory to be written.
- *
- */
-void zpool_obj_write(struct zpool *zpool, unsigned long handle,
-		     void *handle_mem, size_t mem_len)
-{
-	zpool->driver->obj_write(zpool->pool, handle, handle_mem, mem_len);
+	zpool->driver->unpin(zpool->pool, handle);
 }
 
 /**
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 961b270f023c..90ce09bc4d0a 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -23,6 +23,7 @@
  *	zspage->lock
  */
 
+#include <crypto/scatterwalk.h>
 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/sched.h>
@@ -49,6 +50,7 @@
 #include <linux/pagemap.h>
 #include <linux/fs.h>
 #include <linux/local_lock.h>
+#include <linux/scatterlist.h>
 #include "zpdesc.h"
 
 #define ZSPAGE_MAGIC	0x58
@@ -445,7 +447,6 @@ static void record_obj(unsigned long handle, unsigned long obj)
 /* zpool driver */
 
 #ifdef CONFIG_ZPOOL
-
 static void *zs_zpool_create(const char *name, gfp_t gfp)
 {
 	/*
@@ -475,22 +476,15 @@ static void zs_zpool_free(void *pool, unsigned long handle)
 	zs_free(pool, handle);
 }
 
-static void *zs_zpool_obj_read_begin(void *pool, unsigned long handle,
-				     void *local_copy)
+static void zs_zpool_pin(void *pool, unsigned long handle,
+			 struct scatterlist sg[2])
 {
-	return zs_obj_read_begin(pool, handle, local_copy);
+	zs_pin_object(pool, handle, sg);
 }
 
-static void zs_zpool_obj_read_end(void *pool, unsigned long handle,
-				  void *handle_mem)
+static void zs_zpool_unpin(void *pool, unsigned long handle)
 {
-	zs_obj_read_end(pool, handle, handle_mem);
-}
-
-static void zs_zpool_obj_write(void *pool, unsigned long handle,
-			       void *handle_mem, size_t mem_len)
-{
-	zs_obj_write(pool, handle, handle_mem, mem_len);
+	zs_unpin_object(pool, handle);
 }
 
 static u64 zs_zpool_total_pages(void *pool)
@@ -505,9 +499,8 @@ static struct zpool_driver zs_zpool_driver = {
 	.destroy =		  zs_zpool_destroy,
 	.malloc =		  zs_zpool_malloc,
 	.free =			  zs_zpool_free,
-	.obj_read_begin =	  zs_zpool_obj_read_begin,
-	.obj_read_end  =	  zs_zpool_obj_read_end,
-	.obj_write =		  zs_zpool_obj_write,
+	.pin =			  zs_zpool_pin,
+	.unpin =		  zs_zpool_unpin,
 	.total_pages =		  zs_zpool_total_pages,
 };
 
@@ -1145,15 +1138,15 @@ unsigned long zs_get_total_pages(struct zs_pool *pool)
 }
 EXPORT_SYMBOL_GPL(zs_get_total_pages);
 
-void *zs_obj_read_begin(struct zs_pool *pool, unsigned long handle,
-			void *local_copy)
+void zs_pin_object(struct zs_pool *pool, unsigned long handle,
+		   struct scatterlist *sg)
 {
+	int handle_size = ZS_HANDLE_SIZE;
 	struct zspage *zspage;
 	struct zpdesc *zpdesc;
 	unsigned long obj, off;
 	unsigned int obj_idx;
 	struct size_class *class;
-	void *addr;
 
 	/* Guarantee we can get zspage from handle safely */
 	read_lock(&pool->lock);
@@ -1168,107 +1161,43 @@ void *zs_obj_read_begin(struct zs_pool *pool, unsigned long handle,
 	class = zspage_class(pool, zspage);
 	off = offset_in_page(class->size * obj_idx);
 
+	if (ZsHugePage(zspage))
+		handle_size = 0;
+
 	if (off + class->size <= PAGE_SIZE) {
 		/* this object is contained entirely within a page */
-		addr = kmap_local_zpdesc(zpdesc);
-		addr += off;
+		sg_init_table(sg, 1);
+		sg_set_page(sg, zpdesc_page(zpdesc),
+			    class->size - handle_size, off + handle_size);
 	} else {
 		size_t sizes[2];
 
 		/* this object spans two pages */
 		sizes[0] = PAGE_SIZE - off;
 		sizes[1] = class->size - sizes[0];
-		addr = local_copy;
 
-		memcpy_from_page(addr, zpdesc_page(zpdesc),
-				 off, sizes[0]);
+		sg_init_table(sg, 2);
+		sg_set_page(sg, zpdesc_page(zpdesc), sizes[0] - handle_size,
+			    off + handle_size);
 		zpdesc = get_next_zpdesc(zpdesc);
-		memcpy_from_page(addr + sizes[0],
-				 zpdesc_page(zpdesc),
-				 0, sizes[1]);
+		sg_set_page(&sg[1], zpdesc_page(zpdesc), sizes[1], 0);
 	}
-
-	if (!ZsHugePage(zspage))
-		addr += ZS_HANDLE_SIZE;
-
-	return addr;
 }
-EXPORT_SYMBOL_GPL(zs_obj_read_begin);
+EXPORT_SYMBOL_GPL(zs_pin_object);
 
-void zs_obj_read_end(struct zs_pool *pool, unsigned long handle,
-		     void *handle_mem)
+void zs_unpin_object(struct zs_pool *pool, unsigned long handle)
 {
 	struct zspage *zspage;
 	struct zpdesc *zpdesc;
-	unsigned long obj, off;
 	unsigned int obj_idx;
-	struct size_class *class;
+	unsigned long obj;
 
 	obj = handle_to_obj(handle);
 	obj_to_location(obj, &zpdesc, &obj_idx);
 	zspage = get_zspage(zpdesc);
-	class = zspage_class(pool, zspage);
-	off = offset_in_page(class->size * obj_idx);
-
-	if (off + class->size <= PAGE_SIZE) {
-		if (!ZsHugePage(zspage))
-			off += ZS_HANDLE_SIZE;
-		handle_mem -= off;
-		kunmap_local(handle_mem);
-	}
-
 	zspage_read_unlock(zspage);
 }
-EXPORT_SYMBOL_GPL(zs_obj_read_end);
-
-void zs_obj_write(struct zs_pool *pool, unsigned long handle,
-		  void *handle_mem, size_t mem_len)
-{
-	struct zspage *zspage;
-	struct zpdesc *zpdesc;
-	unsigned long obj, off;
-	unsigned int obj_idx;
-	struct size_class *class;
-
-	/* Guarantee we can get zspage from handle safely */
-	read_lock(&pool->lock);
-	obj = handle_to_obj(handle);
-	obj_to_location(obj, &zpdesc, &obj_idx);
-	zspage = get_zspage(zpdesc);
-
-	/* Make sure migration doesn't move any pages in this zspage */
-	zspage_read_lock(zspage);
-	read_unlock(&pool->lock);
-
-	class = zspage_class(pool, zspage);
-	off = offset_in_page(class->size * obj_idx);
-
-	if (off + class->size <= PAGE_SIZE) {
-		/* this object is contained entirely within a page */
-		void *dst = kmap_local_zpdesc(zpdesc);
-
-		if (!ZsHugePage(zspage))
-			off += ZS_HANDLE_SIZE;
-		memcpy(dst + off, handle_mem, mem_len);
-		kunmap_local(dst);
-	} else {
-		/* this object spans two pages */
-		size_t sizes[2];
-
-		off += ZS_HANDLE_SIZE;
-		sizes[0] = PAGE_SIZE - off;
-		sizes[1] = mem_len - sizes[0];
-
-		memcpy_to_page(zpdesc_page(zpdesc), off,
-			       handle_mem, sizes[0]);
-		zpdesc = get_next_zpdesc(zpdesc);
-		memcpy_to_page(zpdesc_page(zpdesc), 0,
-			       handle_mem + sizes[0], sizes[1]);
-	}
-
-	zspage_read_unlock(zspage);
-}
-EXPORT_SYMBOL_GPL(zs_obj_write);
+EXPORT_SYMBOL_GPL(zs_unpin_object);
 
 /**
  * zs_huge_class_size() - Returns the size (in bytes) of the first huge
diff --git a/mm/zswap.c b/mm/zswap.c
index 8b086740698a..42b5fbeea477 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -13,6 +13,8 @@
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#include <crypto/acompress.h>
+#include <crypto/scatterwalk.h>
 #include <linux/module.h>
 #include <linux/cpu.h>
 #include <linux/highmem.h>
@@ -26,7 +28,6 @@
 #include <linux/mempolicy.h>
 #include <linux/mempool.h>
 #include <linux/zpool.h>
-#include <crypto/acompress.h>
 #include <linux/zswap.h>
 #include <linux/mm_types.h>
 #include <linux/page-flags.h>
@@ -147,7 +148,6 @@ struct crypto_acomp_ctx {
 	struct crypto_wait wait;
 	u8 *buffer;
 	struct mutex mutex;
-	bool is_sleepable;
 };
 
 /*
@@ -865,7 +865,6 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
 
 	acomp_ctx->buffer = buffer;
 	acomp_ctx->acomp = acomp;
-	acomp_ctx->is_sleepable = acomp_is_async(acomp);
 	acomp_ctx->req = req;
 	mutex_unlock(&acomp_ctx->mutex);
 	return 0;
@@ -928,6 +927,7 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry,
 	struct scatterlist input, output;
 	int comp_ret = 0, alloc_ret = 0;
 	unsigned int dlen = PAGE_SIZE;
+	struct scatterlist sg[2];
 	unsigned long handle;
 	struct zpool *zpool;
 	gfp_t gfp;
@@ -969,7 +969,9 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry,
 	if (alloc_ret)
 		goto unlock;
 
-	zpool_obj_write(zpool, handle, dst, dlen);
+	zpool_pin_handle(zpool, handle, sg);
+	memcpy_to_sglist(sg, 0, dst, dlen);
+	zpool_unpin_handle(zpool, handle);
 	entry->handle = handle;
 	entry->length = dlen;
 
@@ -988,34 +990,19 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry,
 static void zswap_decompress(struct zswap_entry *entry, struct folio *folio)
 {
 	struct zpool *zpool = entry->pool->zpool;
-	struct scatterlist input, output;
 	struct crypto_acomp_ctx *acomp_ctx;
-	u8 *src, *obj;
+	struct scatterlist input[2];
+	struct scatterlist output;
 
 	acomp_ctx = acomp_ctx_get_cpu_lock(entry->pool);
-	obj = zpool_obj_read_begin(zpool, entry->handle, acomp_ctx->buffer);
-
-	/*
-	 * zpool_obj_read_begin() might return a kmap address of highmem when
-	 * acomp_ctx->buffer is not used.  However, sg_init_one() does not
-	 * handle highmem addresses, so copy the object to acomp_ctx->buffer.
-	 */
-	if (virt_addr_valid(obj)) {
-		src = obj;
-	} else {
-		WARN_ON_ONCE(obj == acomp_ctx->buffer);
-		memcpy(acomp_ctx->buffer, obj, entry->length);
-		src = acomp_ctx->buffer;
-	}
-
-	sg_init_one(&input, src, entry->length);
+	zpool_pin_handle(zpool, entry->handle, input);
 	sg_init_table(&output, 1);
 	sg_set_folio(&output, folio, PAGE_SIZE, 0);
-	acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, PAGE_SIZE);
+	acomp_request_set_params(acomp_ctx->req, input, &output, entry->length, PAGE_SIZE);
 	BUG_ON(crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait));
 	BUG_ON(acomp_ctx->req->dlen != PAGE_SIZE);
 
-	zpool_obj_read_end(zpool, entry->handle, obj);
+	zpool_unpin_handle(zpool, entry->handle);
 	acomp_ctx_put_unlock(acomp_ctx);
 }
 
-- 
2.39.5

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Re: [PATCH mm-unstable 3/5] mm: zpool: Remove object mapping APIs

[Yosry Ahmed]

On Thu, Mar 06, 2025 at 12:19:19PM +0800, Herbert Xu wrote:
> On Thu, Mar 06, 2025 at 09:48:58AM +0800, Herbert Xu wrote:
> >
> > This patch breaks zbud and z3fold because they haven't been converted
> > to the new interface.
> 
> I've rebased my zswap SG patch on top of your series.  I've removed
> all the mapping code from zpool/zsmalloc and pushed it out to zram
> instead.
> 
> This patch depends on a new memcpy_sglist function which I've just
> posted a patch for:
> 
> https://patchwork.kernel.org/project/linux-crypto/patch/Z8kXhLb681E_FLzs@gondor.apana.org.au/
> 
> From a77ee529b831e7e606ed2a5b723b74ce234a3915 Mon Sep 17 00:00:00 2001
> From: Herbert Xu <herbert@gondor.apana.org.au>
> Date: Thu, 6 Mar 2025 12:13:58 +0800
> Subject: [PATCH] mm: zswap: Give non-linear objects to Crypto API
> 
> Instead of copying non-linear objects into a buffer, use the
> scatterlist to give them directly to the Crypto API.
> 
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

The zswap and zsmalloc look good and the code is simpler. I am fine with
this approach if Sergey is fine with it, although I wonder if we should
update Sergey's patches in mm-unstable do this directly. Currently we
are switching from mapping APIs to read/write APIs, and then quickly to
the pinning APIs. The history will be confusing.

Sergey, do you prefer if we keep things as-is, or if you update your
series to incorporate Herbert's changes for zsmalloc/zram, then I can
update my series to incorporate the changes in zswap?

We can also combine the series into a single updated one with
zsmalloc/zram/zswap changes.

Let me know what you prefer.

Re: [PATCH mm-unstable 3/5] mm: zpool: Remove object mapping APIs

[Herbert Xu]

On Thu, Mar 06, 2025 at 04:55:07PM +0000, Yosry Ahmed wrote:
>
> The zswap and zsmalloc look good and the code is simpler. I am fine with
> this approach if Sergey is fine with it, although I wonder if we should
> update Sergey's patches in mm-unstable do this directly. Currently we
> are switching from mapping APIs to read/write APIs, and then quickly to
> the pinning APIs. The history will be confusing.
> 
> Sergey, do you prefer if we keep things as-is, or if you update your
> series to incorporate Herbert's changes for zsmalloc/zram, then I can
> update my series to incorporate the changes in zswap?
> 
> We can also combine the series into a single updated one with
> zsmalloc/zram/zswap changes.
> 
> Let me know what you prefer.

This patch is only illustrating what zswap would look like once we
move to an SG-based interface.  So I'm not actually submitting it
for inclusion at this time.

Sergey has volunteed to add parameter support to acomp.  Let's
wait for that before making these changes to zsmalloc/zswap.

Thanks,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Re: [PATCH mm-unstable 3/5] mm: zpool: Remove object mapping APIs

[Sergey Senozhatsky]

On (25/03/07 10:38), Herbert Xu wrote:
> On Thu, Mar 06, 2025 at 04:55:07PM +0000, Yosry Ahmed wrote:
> >
> > The zswap and zsmalloc look good and the code is simpler. I am fine with
> > this approach if Sergey is fine with it, although I wonder if we should
> > update Sergey's patches in mm-unstable do this directly. Currently we
> > are switching from mapping APIs to read/write APIs, and then quickly to
> > the pinning APIs. The history will be confusing.
> > 
> > Sergey, do you prefer if we keep things as-is, or if you update your
> > series to incorporate Herbert's changes for zsmalloc/zram, then I can
> > update my series to incorporate the changes in zswap?
> > 
> > We can also combine the series into a single updated one with
> > zsmalloc/zram/zswap changes.
> > 
> > Let me know what you prefer.
> 
> This patch is only illustrating what zswap would look like once we
> move to an SG-based interface.  So I'm not actually submitting it
> for inclusion at this time.

Ah, OK, that's good to know, I was also a bit puzzled.
Perhaps next time we can label such patches as "POC" or
something.

> Sergey has volunteed to add parameter support to acomp.  Let's
> wait for that before making these changes to zsmalloc/zswap.

Yup, I'll keep you posted (once I have something.)

Re: [PATCH mm-unstable 3/5] mm: zpool: Remove object mapping APIs

[Johannes Weiner]

On Thu, Mar 06, 2025 at 09:48:58AM +0800, Herbert Xu wrote:
> On Wed, Mar 05, 2025 at 06:11:31AM +0000, Yosry Ahmed wrote:
> > zpool_map_handle(), zpool_unmap_handle(), and zpool_can_sleep_mapped()
> > are no longer used. Remove them with the underlying driver callbacks.
> > 
> > Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
> > ---
> >  include/linux/zpool.h | 30 ---------------------
> >  mm/zpool.c            | 61 -------------------------------------------
> >  mm/zsmalloc.c         | 27 -------------------
> >  3 files changed, 118 deletions(-)
> 
> This patch breaks zbud and z3fold because they haven't been converted
> to the new interface.

They're both scheduled for removal and already gone in the mm tree.

Re: [PATCH mm-unstable 5/5] mm: zpool: Remove zpool_malloc_support_movable()

[Sergey Senozhatsky]

On (25/03/05 06:11), Yosry Ahmed wrote:
> zpool_malloc_support_movable() always returns true for zsmalloc, the
> only remaining zpool driver. Remove it and set the gfp flags in
> zswap_compress() accordingly. Opportunistically use GFP_NOWAIT instead
> of __GFP_NOWARN | __GFP_KSWAPD_RECLAIM for conciseness as they are
> equivalent.
> 
> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>

Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>

Re: [PATCH mm-unstable 5/5] mm: zpool: Remove zpool_malloc_support_movable()

[Johannes Weiner]

On Wed, Mar 05, 2025 at 06:11:33AM +0000, Yosry Ahmed wrote:
> zpool_malloc_support_movable() always returns true for zsmalloc, the
> only remaining zpool driver. Remove it and set the gfp flags in
> zswap_compress() accordingly. Opportunistically use GFP_NOWAIT instead
> of __GFP_NOWARN | __GFP_KSWAPD_RECLAIM for conciseness as they are
> equivalent.
> 
> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Re: [PATCH mm-unstable 5/5] mm: zpool: Remove zpool_malloc_support_movable()

[Nhat Pham]

On Tue, Mar 4, 2025 at 10:12 PM Yosry Ahmed <yosry.ahmed@linux.dev> wrote:
>
> zpool_malloc_support_movable() always returns true for zsmalloc, the
> only remaining zpool driver. Remove it and set the gfp flags in
> zswap_compress() accordingly. Opportunistically use GFP_NOWAIT instead
> of __GFP_NOWARN | __GFP_KSWAPD_RECLAIM for conciseness as they are
> equivalent.
>
> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>

Acked-by: Nhat Pham <nphamcs@gmail.com>

Re: [PATCH mm-unstable 4/5] mm: zsmalloc: Remove object mapping APIs and per-CPU map areas

[Sergey Senozhatsky]

On (25/03/05 06:11), Yosry Ahmed wrote:
> zs_map_object() and zs_unmap_object() are no longer used, remove them.
> Since these are the only users of per-CPU mapping_areas, remove them and
> the associated CPU hotplug callbacks too.
> 
> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>

Acked-by: Sergey Senozhatsky <senozhatsky@chromium.org>

Re: [PATCH mm-unstable 4/5] mm: zsmalloc: Remove object mapping APIs and per-CPU map areas

[Johannes Weiner]

On Wed, Mar 05, 2025 at 06:11:32AM +0000, Yosry Ahmed wrote:
> zs_map_object() and zs_unmap_object() are no longer used, remove them.
> Since these are the only users of per-CPU mapping_areas, remove them and
> the associated CPU hotplug callbacks too.
> 
> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Re: [PATCH mm-unstable 4/5] mm: zsmalloc: Remove object mapping APIs and per-CPU map areas

[Nhat Pham]

On Tue, Mar 4, 2025 at 10:12 PM Yosry Ahmed <yosry.ahmed@linux.dev> wrote:
>
> zs_map_object() and zs_unmap_object() are no longer used, remove them.
> Since these are the only users of per-CPU mapping_areas, remove them and
> the associated CPU hotplug callbacks too.
>
> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>

Acked-by: Nhat Pham <nphamcs@gmail.com>

Re: [PATCH mm-unstable 4/5] mm: zsmalloc: Remove object mapping APIs and per-CPU map areas

[Yosry Ahmed]

On Wed, Mar 05, 2025 at 06:11:32AM +0000, Yosry Ahmed wrote:
> zs_map_object() and zs_unmap_object() are no longer used, remove them.
> Since these are the only users of per-CPU mapping_areas, remove them and
> the associated CPU hotplug callbacks too.
> 
> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
> ---
>  include/linux/cpuhotplug.h |   1 -
>  include/linux/zsmalloc.h   |  21 ----
>  mm/zsmalloc.c              | 226 +------------------------------------
>  3 files changed, 1 insertion(+), 247 deletions(-)

I missed updating the docs. Andrew, could you please squash the
following diff in? I intentionally did not state the name of the new
APIs to avoid needing to update the docs with similar changes in the
future:

diff --git a/Documentation/mm/zsmalloc.rst b/Documentation/mm/zsmalloc.rst
index 76902835e68e9..d2bbecd78e146 100644
--- a/Documentation/mm/zsmalloc.rst
+++ b/Documentation/mm/zsmalloc.rst
@@ -27,9 +27,8 @@ Instead, it returns an opaque handle (unsigned long) which encodes actual
 location of the allocated object. The reason for this indirection is that
 zsmalloc does not keep zspages permanently mapped since that would cause
 issues on 32-bit systems where the VA region for kernel space mappings
-is very small. So, before using the allocating memory, the object has to
-be mapped using zs_map_object() to get a usable pointer and subsequently
-unmapped using zs_unmap_object().
+is very small. So, using the allocated memory should be done through the
+proper handle-based APIs.

 stat
 ====