linux-kernel - [PATCH] proc: fixup PDE allocation bloat

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Date:   Mon, 18 Jun 2018 00:57:33 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     dhowells@...hat.com, viro@...iv.linux.org.uk,
        akpm@...ux-foundation.org
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] proc: fixup PDE allocation bloat

commit 24074a35c5c975c94cd9691ae962855333aac47f
("proc: Make inline name size calculation automatic")
started to put PDE allocations into kmalloc-256 which is unnecessary as
~40 character names are very rare.

Put allocation back into kmalloc-192 cache for 64-bit non-debug builds.

Put BUILD_BUG_ON to know when PDE size is gotten out of control.

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---

 fs/proc/inode.c    |    6 ++++--
 fs/proc/internal.h |   17 +++++++----------
 2 files changed, 11 insertions(+), 12 deletions(-)

--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -105,8 +105,10 @@ void __init proc_init_kmemcache(void)
 		kmem_cache_create("pde_opener", sizeof(struct pde_opener), 0,
 				  SLAB_ACCOUNT|SLAB_PANIC, NULL);
 	proc_dir_entry_cache = kmem_cache_create_usercopy(
-		"proc_dir_entry", SIZEOF_PDE_SLOT, 0, SLAB_PANIC,
-		OFFSETOF_PDE_NAME, SIZEOF_PDE_INLINE_NAME, NULL);
+		"proc_dir_entry", SIZEOF_PDE, 0, SLAB_PANIC,
+		offsetof(struct proc_dir_entry, inline_name),
+		SIZEOF_PDE_INLINE_NAME, NULL);
+	BUILD_BUG_ON(sizeof(struct proc_dir_entry) >= SIZEOF_PDE);
 }
 
 static int proc_show_options(struct seq_file *seq, struct dentry *root)
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -65,16 +65,13 @@ struct proc_dir_entry {
 	char inline_name[];
 } __randomize_layout;
 
-#define OFFSETOF_PDE_NAME offsetof(struct proc_dir_entry, inline_name)
-#define SIZEOF_PDE_SLOT					\
-	(OFFSETOF_PDE_NAME + 34 <= 64 ? 64 :		\
-	 OFFSETOF_PDE_NAME + 34 <= 128 ? 128 :		\
-	 OFFSETOF_PDE_NAME + 34 <= 192 ? 192 :		\
-	 OFFSETOF_PDE_NAME + 34 <= 256 ? 256 :		\
-	 OFFSETOF_PDE_NAME + 34 <= 512 ? 512 :		\
-	 0)
-
-#define SIZEOF_PDE_INLINE_NAME (SIZEOF_PDE_SLOT - OFFSETOF_PDE_NAME)
+#ifdef CONFIG_64BIT
+#define SIZEOF_PDE	(sizeof(spinlock_t) <= 4 ? 192 : 256)
+#else
+#define SIZEOF_PDE	(sizeof(spinlock_t) <= 4 ? 128 : 192)
+#endif
+
+#define SIZEOF_PDE_INLINE_NAME (SIZEOF_PDE - sizeof(struct proc_dir_entry))
 
 extern struct kmem_cache *proc_dir_entry_cache;
 void pde_free(struct proc_dir_entry *pde);