linux-kernel - Re: [PATCH] Save some bytes in mm_struct by filling holes on 64bit

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Date:	Wed, 12 Mar 2008 19:38:05 +0100
From:	Andi Kleen <ak@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Save some bytes in mm_struct by filling holes on 64bit


> The current ioctx_list_lock position is better from a cache layout POV?

Hmm ok you're right perhaps it's better to move core_waiters up
instead. Updated  patch
Save some bytes in mm_struct by filling holes v2

Putting int values together for better packing on 64bit 
shrinks sizeof(struct mm_struct) from 776 bytes to 760 bytes.

Signed-off-by: Andi Kleen <ak@...e.de>

Index: linux-2.6.25-rc5/include/linux/mm_types.h
===================================================================
--- linux-2.6.25-rc5.orig/include/linux/mm_types.h
+++ linux-2.6.25-rc5/include/linux/mm_types.h
@@ -172,6 +172,7 @@ struct mm_struct {
 	atomic_t mm_users;			/* How many users with user space? */
 	atomic_t mm_count;			/* How many references to "struct mm_struct" (users 
count as 1) */
 	int map_count;				/* number of VMAs */
+	int core_waiters;
 	struct rw_semaphore mmap_sem;
 	spinlock_t page_table_lock;		/* Protects page tables and some counters */
 
@@ -216,11 +217,10 @@ struct mm_struct {
 	unsigned long flags; /* Must use atomic bitops to access the bits */
 
 	/* coredumping support */
-	int core_waiters;
 	struct completion *core_startup_done, core_done;
 
 	/* aio bits */
-	rwlock_t		ioctx_list_lock;
+	rwlock_t		ioctx_list_lock;	/* aio lock */
 	struct kioctx		*ioctx_list;
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
 	struct mem_cgroup *mem_cgroup;
--
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