+ zram-convert-to-sg-list-zsmalloc-object-read-api.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: zram: convert to SG-list zsmalloc object read API
has been added to the -mm mm-new branch.  Its filename is
     zram-convert-to-sg-list-zsmalloc-object-read-api.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/zram-convert-to-sg-list-zsmalloc-object-read-api.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Sergey Senozhatsky <senozhatsky@chromium.org>
Subject: zram: convert to SG-list zsmalloc object read API
Date: Mon, 7 Sep 2026 19:57:28 +0900

Patch series "zsmallc: remove old object read API".

zram remains the only user of old zsmalloc object read API.  This series
removes the old API and converts zram to use the new SG-list based API.


This patch (of 2):

zram remains the last user of old zsmalloc object read API, that performed
linearisation on the zsmalloc side.  There is a new SG-list API, that has
a bunch of benefits.  Switch zram to SG-list zsmalloc object read API.

Link: https://lore.kernel.org/20260907105739.1793316-1-senozhatsky@chromium.org
Link: https://lore.kernel.org/20260907105739.1793316-2-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 drivers/block/zram/zcomp.c    |   23 +++++++++++--
 drivers/block/zram/zcomp.h    |    4 +-
 drivers/block/zram/zram_drv.c |   56 ++++++++++++++++++--------------
 3 files changed, 55 insertions(+), 28 deletions(-)

--- a/drivers/block/zram/zcomp.c~zram-convert-to-sg-list-zsmalloc-object-read-api
+++ a/drivers/block/zram/zcomp.c
@@ -7,6 +7,8 @@
 #include <linux/wait.h>
 #include <linux/sched.h>
 #include <linux/cpuhotplug.h>
+#include <linux/highmem.h>
+#include <linux/scatterlist.h>
 #include <linux/vmalloc.h>
 #include <linux/sysfs.h>
 
@@ -158,17 +160,32 @@ int zcomp_compress(struct zcomp *comp, s
 }
 
 int zcomp_decompress(struct zcomp *comp, struct zcomp_strm *zstrm,
-		     const void *src, unsigned int src_len, void *dst)
+		     struct scatterlist *sg, unsigned int src_len, void *dst)
 {
 	struct zcomp_req req = {
-		.src = src,
 		.dst = dst,
 		.src_len = src_len,
 		.dst_len = PAGE_SIZE,
 	};
+	void *src = NULL;
+	int ret;
 
 	might_sleep();
-	return comp->ops->decompress(comp->params, &zstrm->ctx, &req);
+
+	if (sg_is_last(sg)) {
+		/* the object is contained within one page, read it in-place */
+		src = kmap_local_page(sg_page(sg));
+		req.src = src + sg->offset;
+	} else {
+		/* the object spans two pages, linearize it into local copy */
+		sg_copy_to_buffer(sg, 2, zstrm->local_copy, src_len);
+		req.src = zstrm->local_copy;
+	}
+
+	ret = comp->ops->decompress(comp->params, &zstrm->ctx, &req);
+	if (src)
+		kunmap_local(src);
+	return ret;
 }
 
 int zcomp_cpu_up_prepare(unsigned int cpu, struct hlist_node *node)
--- a/drivers/block/zram/zcomp.h~zram-convert-to-sg-list-zsmalloc-object-read-api
+++ a/drivers/block/zram/zcomp.h
@@ -5,6 +5,8 @@
 
 #include <linux/mutex.h>
 
+struct scatterlist;
+
 #define ZCOMP_PARAM_NOT_SET	INT_MIN
 
 struct deflate_params {
@@ -91,6 +93,6 @@ void zcomp_stream_put(struct zcomp_strm
 int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
 		   const void *src, unsigned int *dst_len);
 int zcomp_decompress(struct zcomp *comp, struct zcomp_strm *zstrm,
-		     const void *src, unsigned int src_len, void *dst);
+		     struct scatterlist *sg, unsigned int src_len, void *dst);
 
 #endif /* _ZCOMP_H_ */
--- a/drivers/block/zram/zram_drv.c~zram-convert-to-sg-list-zsmalloc-object-read-api
+++ a/drivers/block/zram/zram_drv.c
@@ -32,6 +32,7 @@
 #include <linux/debugfs.h>
 #include <linux/cpuhotplug.h>
 #include <linux/part_stat.h>
+#include <linux/scatterlist.h>
 #include <linux/kernel_read_file.h>
 #include <linux/rcupdate.h>
 
@@ -1347,9 +1348,9 @@ static int decompress_bdev_page(struct z
 				unsigned long index)
 {
 	struct zcomp_strm *zstrm;
+	struct scatterlist sg[1];
 	unsigned int size;
 	int ret, prio;
-	void *src;
 
 	slot_lock(zram, index);
 	/* Since slot was unlocked we need to make sure it's still ZRAM_WB */
@@ -1368,13 +1369,18 @@ static int decompress_bdev_page(struct z
 	size = get_slot_size(zram, index);
 	prio = get_slot_comp_priority(zram, index);
 
+	sg_init_table(sg, 1);
+	sg_set_page(sg, page, size, 0);
+
 	zstrm = zcomp_stream_get(zram->comps[prio]);
-	src = kmap_local_page(page);
-	ret = zcomp_decompress(zram->comps[prio], zstrm, src, size,
+	ret = zcomp_decompress(zram->comps[prio], zstrm, sg, size,
 			       zstrm->local_copy);
-	if (!ret)
-		copy_page(src, zstrm->local_copy);
-	kunmap_local(src);
+	if (!ret) {
+		void *dst = kmap_local_page(page);
+
+		copy_page(dst, zstrm->local_copy);
+		kunmap_local(dst);
+	}
 	zcomp_stream_put(zstrm);
 	slot_unlock(zram, index);
 
@@ -2086,15 +2092,19 @@ static int read_same_filled_page(struct
 static int read_incompressible_page(struct zram *zram, struct page *page,
 				    unsigned long index)
 {
+	struct scatterlist sg[2];
 	unsigned long handle;
 	void *src, *dst;
 
 	handle = get_slot_handle(zram, index);
-	src = zs_obj_read_begin(zram->mem_pool, handle, PAGE_SIZE, NULL);
+	zs_obj_read_sg_begin(zram->mem_pool, handle, sg, PAGE_SIZE);
+	/* an incompressible object never spans two pages */
+	src = kmap_local_page(sg_page(sg));
 	dst = kmap_local_page(page);
 	copy_page(dst, src);
 	kunmap_local(dst);
-	zs_obj_read_end(zram->mem_pool, handle, PAGE_SIZE, src);
+	kunmap_local(src);
+	zs_obj_read_sg_end(zram->mem_pool, handle);
 
 	return 0;
 }
@@ -2103,9 +2113,10 @@ static int read_compressed_page(struct z
 				unsigned long index)
 {
 	struct zcomp_strm *zstrm;
+	struct scatterlist sg[2];
 	unsigned long handle;
 	unsigned int size;
-	void *src, *dst;
+	void *dst;
 	int ret, prio;
 
 	handle = get_slot_handle(zram, index);
@@ -2113,12 +2124,11 @@ static int read_compressed_page(struct z
 	prio = get_slot_comp_priority(zram, index);
 
 	zstrm = zcomp_stream_get(zram->comps[prio]);
-	src = zs_obj_read_begin(zram->mem_pool, handle, size,
-				zstrm->local_copy);
+	zs_obj_read_sg_begin(zram->mem_pool, handle, sg, size);
 	dst = kmap_local_page(page);
-	ret = zcomp_decompress(zram->comps[prio], zstrm, src, size, dst);
+	ret = zcomp_decompress(zram->comps[prio], zstrm, sg, size, dst);
 	kunmap_local(dst);
-	zs_obj_read_end(zram->mem_pool, handle, size, src);
+	zs_obj_read_sg_end(zram->mem_pool, handle);
 	zcomp_stream_put(zstrm);
 
 	return ret;
@@ -2128,25 +2138,23 @@ static int read_compressed_page(struct z
 static int read_from_zspool_raw(struct zram *zram, struct page *page,
 				unsigned long index)
 {
-	struct zcomp_strm *zstrm;
+	struct scatterlist sg[2];
 	unsigned long handle;
 	unsigned int size;
-	void *src;
+	void *dst;
 
 	handle = get_slot_handle(zram, index);
 	size = get_slot_size(zram, index);
 
 	/*
-	 * We need to get stream just for ->local_copy buffer, in
-	 * case if object spans two physical pages. No decompression
-	 * takes place here, as we read raw compressed data.
+	 * No decompression takes place here, we copy out raw compressed
+	 * data directly into the destination page.
 	 */
-	zstrm = zcomp_stream_get(zram->comps[ZRAM_PRIMARY_COMP]);
-	src = zs_obj_read_begin(zram->mem_pool, handle, size,
-				zstrm->local_copy);
-	memcpy_to_page(page, 0, src, size);
-	zs_obj_read_end(zram->mem_pool, handle, size, src);
-	zcomp_stream_put(zstrm);
+	zs_obj_read_sg_begin(zram->mem_pool, handle, sg, size);
+	dst = kmap_local_page(page);
+	sg_copy_to_buffer(sg, sg_nents(sg), dst, size);
+	kunmap_local(dst);
+	zs_obj_read_sg_end(zram->mem_pool, handle);
 
 	memzero_page(page, size, PAGE_SIZE - size);
 
_

Patches currently in -mm which might be from senozhatsky@chromium.org are

zram-remove-unreachable-kernel_read_file_from_path-return-check.patch
zram-convert-to-sg-list-zsmalloc-object-read-api.patch
zsmalloc-remove-old-object-read-api.patch