+ zram-zstd-do-not-use-kvzalloc-for-zstd-allocations.patch added to mm-nonmm-unstable branch

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

The patch titled
     Subject: zram: zstd: do not use kvzalloc() for zstd allocations
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     zram-zstd-do-not-use-kvzalloc-for-zstd-allocations.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/zram-zstd-do-not-use-kvzalloc-for-zstd-allocations.patch

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

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------------------------------------------------------
From: Sergey Senozhatsky <senozhatsky@chromium.org>
Subject: zram: zstd: do not use kvzalloc() for zstd allocations
Date: Sun, 25 Oct 2026 11:18:26 +0900

When a dictionary is configured, zstd allocates all of its memory (C/D
dictionaries, compression and decompression contexts and compression
workspaces) via zstd_custom_alloc().  zstd_custom_alloc() uses
kvzalloc(), which falls back to vmalloc() only when kmalloc() fails,
and kmalloc() rounds such sizes up to a power-of-two number of pages.

For example, on x86_64 with a 110K dictionary, switching from
kvzalloc() to __vmalloc() reduces allocations from:
- CDict (level 3):            512 KB -> 400 KB
- CDict (levels 12+):        2048 KB -> 1552 KB
- DCtx (per-CPU):             128 KB -> 96 KB
- CCtx workspace (level 3):   128 KB -> 84 KB (per-CPU)
- CCtx workspace (level 14+): 1024 KB -> 764 KB (per-CPU)

Use __vmalloc() for allocations larger than PAGE_SIZE (and kzalloc()
for smaller ones), which is also how zram allocates zstd workspaces
when no dictionary is configured.  zstd_custom_free() already uses
kvfree(), which handles both.

Link: https://lore.kernel.org/20261025021839.1542805-11-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Brian Geffon <bgeffon@google.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Bo Zhang <zhangbo0325@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Richard Chang <richardycc@google.com>
Cc: Bo Zhang <zhangbo56@xiaomi.com>
Cc: Hillf Danton <hdanton@sina.com>
---

 drivers/block/zram/backend_zstd.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/drivers/block/zram/backend_zstd.c~zram-zstd-do-not-use-kvzalloc-for-zstd-allocations
+++ a/drivers/block/zram/backend_zstd.c
@@ -26,10 +26,17 @@ struct zstd_params {
 /*
  * For C/D dictionaries we need to provide zstd with zstd_custom_mem,
  * which zstd uses internally to allocate/free memory when needed.
+ *
+ * zstd allocations (C/D dictionaries and contexts) are large and
+ * long-lived.  Don't use kvzalloc() for them: when enough physically
+ * contiguous memory is available it serves them from kmalloc(), which
+ * rounds them up to a power-of-two number of pages.
  */
 static void *zstd_custom_alloc(void *opaque, size_t size)
 {
-	return kvzalloc(size, GFP_NOIO | __GFP_NOWARN);
+	if (size <= PAGE_SIZE)
+		return kzalloc(size, GFP_NOIO | __GFP_NOWARN);
+	return __vmalloc(size, GFP_NOIO | __GFP_NOWARN | __GFP_ZERO);
 }
 
 static void zstd_custom_free(void *opaque, void *address)
_

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

zram-prefix-backends-printk-s.patch
zram-remove-debugfs-entry-on-init-failure.patch
zram-reset-writeback-state-in-zram_reset_device.patch
zram-move-mark_slot_accessed-under-existing-slot-lock-sections.patch
zram-remove-stale-warn_on-from-zram_read_page.patch
zram-zstd-do-not-allocate-empty-c-d-dictionaries.patch
zram-lz4hc-pre-initialize-dictionary-stream-in-setup_params.patch
zram-lz4-use-lz4_decompress_safe_usingdict.patch
zram-lz4hc-use-lz4_decompress_safe_usingdict.patch
zram-zstd-do-not-use-kvzalloc-for-zstd-allocations.patch
zram-split-zcomp-into-separate-r-w-streams.patch
zram-introduce-shared-decompression-streams.patch
zram-allocate-bounce-buffer-for-spanning-objects.patch
zram-borrow-idle-decompression-streams-in-exclusive-mode.patch
zram-use-a-singleton-compression-context-for-recompression.patch