+ mm-list_lru-make-the-case-where-mlru-is-null-as-unlikely.patch added to mm-unstable branch

+ mm-list_lru-make-the-case-where-mlru-is-null-as-unlikely.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/list_lru: make the case where mlru is NULL as unlikely
has been added to the -mm mm-unstable branch.  Its filename is
     mm-list_lru-make-the-case-where-mlru-is-null-as-unlikely.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-list_lru-make-the-case-where-mlru-is-null-as-unlikely.patch

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

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------------------------------------------------------
From: Zeng Jingxiang <linuszeng@tencent.com>
Subject: mm/list_lru: make the case where mlru is NULL as unlikely
Date: Thu, 27 Feb 2025 16:22:23 +0800

In the following memcg_list_lru_alloc() function, mlru here is almost
always NULL, so in most cases this should save a function call, mark mlru
as unlikely to optimize the code, and reusing the mlru for the next
attempt when the tree insertion fails.

        do {
                xas_lock_irqsave(&xas, flags);
                if (!xas_load(&xas) && !css_is_dying(&pos->css)) {
                        xas_store(&xas, mlru);
                        if (!xas_error(&xas))
                                mlru = NULL;
                }
                xas_unlock_irqrestore(&xas, flags);
        } while (xas_nomem(&xas, GFP_KERNEL));
>       if (mlru)
                kfree(mlru);

Link: https://lkml.kernel.org/r/20250227082223.1173847-1-jingxiangzeng.cas@gmail.com
Signed-off-by: Zeng Jingxiang <linuszeng@tencent.com>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202412290924.UTP7GH2Z-lkp@intel.com/
Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Jingxiang Zeng <linuszeng@tencent.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/list_lru.c |   15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

--- a/mm/list_lru.c~mm-list_lru-make-the-case-where-mlru-is-null-as-unlikely
+++ a/mm/list_lru.c
@@ -510,7 +510,7 @@ int memcg_list_lru_alloc(struct mem_cgro
 			 gfp_t gfp)
 {
 	unsigned long flags;
-	struct list_lru_memcg *mlru;
+	struct list_lru_memcg *mlru = NULL;
 	struct mem_cgroup *pos, *parent;
 	XA_STATE(xas, &lru->xa, 0);
 
@@ -535,9 +535,11 @@ int memcg_list_lru_alloc(struct mem_cgro
 			parent = parent_mem_cgroup(pos);
 		}
 
-		mlru = memcg_init_list_lru_one(lru, gfp);
-		if (!mlru)
-			return -ENOMEM;
+		if (!mlru) {
+			mlru = memcg_init_list_lru_one(lru, gfp);
+			if (!mlru)
+				return -ENOMEM;
+		}
 		xas_set(&xas, pos->kmemcg_id);
 		do {
 			xas_lock_irqsave(&xas, flags);
@@ -548,10 +550,11 @@ int memcg_list_lru_alloc(struct mem_cgro
 			}
 			xas_unlock_irqrestore(&xas, flags);
 		} while (xas_nomem(&xas, gfp));
-		if (mlru)
-			kfree(mlru);
 	} while (pos != memcg && !css_is_dying(&pos->css));
 
+	if (unlikely(mlru))
+		kfree(mlru);
+
 	return xas_error(&xas);
 }
 #else
_

Patches currently in -mm which might be from linuszeng@tencent.com are

mm-list_lru-make-the-case-where-mlru-is-null-as-unlikely.patch