linux-kernel - Re: [PATCH v2] zsmalloc: prefer the the original page's node for compressed data

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Message-ID: <mnvexa7kseswglcqbhlot4zg3b3la2ypv2rimdl5mh5glbmhvz@wi6bgqn47hge>
Date: Thu, 3 Apr 2025 12:55:46 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Nhat Pham <nphamcs@...il.com>
Cc: akpm@...ux-foundation.org, hannes@...xchg.org, yosry.ahmed@...ux.dev, 
	chengming.zhou@...ux.dev, sj@...nel.org, linux-mm@...ck.org, kernel-team@...a.com, 
	linux-kernel@...r.kernel.org, gourry@...rry.net, ying.huang@...ux.alibaba.com, 
	jonathan.cameron@...wei.com, dan.j.williams@...el.com, linux-cxl@...r.kernel.org, 
	minchan@...nel.org, senozhatsky@...omium.org
Subject: Re: [PATCH v2] zsmalloc: prefer the the original page's node for
 compressed data

On (25/04/02 13:44), Nhat Pham wrote:
[..]
> @@ -1981,10 +1981,15 @@ static int recompress_slot(struct zram *zram, u32 index, struct page *page,
>  	 * We are holding per-CPU stream mutex and entry lock so better
>  	 * avoid direct reclaim.  Allocation error is not fatal since
>  	 * we still have the old object in the mem_pool.
> +	 *
> +	 * XXX: technically, the node we really want here is the node that holds
> +	 * the original compressed data. But that would require us to modify
> +	 * zsmalloc API to return this information. For now, we will make do with
> +	 * the node of the page allocated for recompression.
>  	 */
>  	handle_new = zs_malloc(zram->mem_pool, comp_len_new,
>  			       GFP_NOIO | __GFP_NOWARN |
> -			       __GFP_HIGHMEM | __GFP_MOVABLE);
> +			       __GFP_HIGHMEM | __GFP_MOVABLE, page_to_nid(page));

This works for me.  I saw in other threads (and sorry, I'm on a sick
leave now, can't reply fast) that "zram people need to fix it"/etc.
I guess I'm one of those zram people and I don't think I run any
multi-node NUMA systems, so that problem probably has never occurred
to me.  We can add a simple API extension to lookup node-id by
zsmalloc handle, if anyone really needs it, but I'm okay with the
status quo (and XXX) for the time being.

[..]
> -unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp)
> +unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp,
> +				const int nid)
>  {

I'm not the zspool maintainer, but if I may ask, for new zsmalloc code my
preference is to follow the kernel styles (yes, the old code doesn't follow
any at all, whenever I touch the old code I fix it).

Do you mind if we do something like below? (at least for zsmalloc)

With this
Acked-by: Sergey Senozhatsky <senozhatsky@...omium.org> #zram and zsmalloc


---

diff --git a/include/linux/zpool.h b/include/linux/zpool.h
index 697525cb00bd..369ef068fad8 100644
--- a/include/linux/zpool.h
+++ b/include/linux/zpool.h
@@ -22,7 +22,7 @@ const char *zpool_get_type(struct zpool *pool);
 void zpool_destroy_pool(struct zpool *pool);
 
 int zpool_malloc(struct zpool *pool, size_t size, gfp_t gfp,
-			unsigned long *handle, const int nid);
+		 unsigned long *handle, const int nid);
 
 void zpool_free(struct zpool *pool, unsigned long handle);
 
@@ -64,7 +64,7 @@ struct zpool_driver {
 	void (*destroy)(void *pool);
 
 	int (*malloc)(void *pool, size_t size, gfp_t gfp,
-				unsigned long *handle, const int nid);
+		      unsigned long *handle, const int nid);
 	void (*free)(void *pool, unsigned long handle);
 
 	void *(*obj_read_begin)(void *pool, unsigned long handle,
diff --git a/mm/zpool.c b/mm/zpool.c
index b99a7c03e735..0a71d03369f1 100644
--- a/mm/zpool.c
+++ b/mm/zpool.c
@@ -239,7 +239,7 @@ const char *zpool_get_type(struct zpool *zpool)
  * Returns: 0 on success, negative value on error.
  */
 int zpool_malloc(struct zpool *zpool, size_t size, gfp_t gfp,
-			unsigned long *handle, const int nid)
+		 unsigned long *handle, const int nid)
 {
 	return zpool->driver->malloc(zpool->pool, size, gfp, handle, nid);
 }
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index daa16ce4cf07..70406ac94bbd 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -452,7 +452,7 @@ static void zs_zpool_destroy(void *pool)
 }
 
 static int zs_zpool_malloc(void *pool, size_t size, gfp_t gfp,
-			unsigned long *handle, const int nid)
+			   unsigned long *handle, const int nid)
 {
 	*handle = zs_malloc(pool, size, gfp, nid);
 
@@ -1033,8 +1033,8 @@ static void create_page_chain(struct size_class *class, struct zspage *zspage,
  * Allocate a zspage for the given size class
  */
 static struct zspage *alloc_zspage(struct zs_pool *pool,
-					struct size_class *class,
-					gfp_t gfp, const int nid)
+				   struct size_class *class,
+				   gfp_t gfp, const int nid)
 {
 	int i;
 	struct zpdesc *zpdescs[ZS_MAX_PAGES_PER_ZSPAGE];
@@ -1333,7 +1333,7 @@ static unsigned long obj_malloc(struct zs_pool *pool,
  * Allocation requests with size > ZS_MAX_ALLOC_SIZE will fail.
  */
 unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp,
-				const int nid)
+			const int nid)
 {
 	unsigned long handle;
 	struct size_class *class;