From efed20a2b9d186be95c824d9f918920f36f3b138 Mon Sep 17 00:00:00 2001
From: Hugh Dickins <hugh@veritas.com>
Date: Mon, 13 Apr 2009 14:40:12 -0700
Subject: [PATCH] --- yaml --- r: 143222 b: refs/heads/master c:
 caefba1740d8016e6dfe8fda84f85bdcb8f8c85d h: refs/heads/master v: v3

---
 [refs]           |  2 +-
 trunk/mm/shmem.c | 25 ++++++++++++++++++++-----
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/[refs] b/[refs]
index f562e9436324..fd2b10b85c4f 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 61609d01cbb3ab865c8cccaf85e6837c47096480
+refs/heads/master: caefba1740d8016e6dfe8fda84f85bdcb8f8c85d
diff --git a/trunk/mm/shmem.c b/trunk/mm/shmem.c
index 28024ce8b8fd..f9cb20ebb990 100644
--- a/trunk/mm/shmem.c
+++ b/trunk/mm/shmem.c
@@ -24,6 +24,7 @@
 #include <linux/init.h>
 #include <linux/vfs.h>
 #include <linux/mount.h>
+#include <linux/pagemap.h>
 #include <linux/file.h>
 #include <linux/mm.h>
 #include <linux/module.h>
@@ -43,7 +44,6 @@ static struct vfsmount *shm_mnt;
 #include <linux/exportfs.h>
 #include <linux/generic_acl.h>
 #include <linux/mman.h>
-#include <linux/pagemap.h>
 #include <linux/string.h>
 #include <linux/slab.h>
 #include <linux/backing-dev.h>
@@ -65,13 +65,28 @@ static struct vfsmount *shm_mnt;
 #include <asm/div64.h>
 #include <asm/pgtable.h>
 
+/*
+ * The maximum size of a shmem/tmpfs file is limited by the maximum size of
+ * its triple-indirect swap vector - see illustration at shmem_swp_entry().
+ *
+ * With 4kB page size, maximum file size is just over 2TB on a 32-bit kernel,
+ * but one eighth of that on a 64-bit kernel.  With 8kB page size, maximum
+ * file size is just over 4TB on a 64-bit kernel, but 16TB on a 32-bit kernel,
+ * MAX_LFS_FILESIZE being then more restrictive than swap vector layout.
+ *
+ * We use / and * instead of shifts in the definitions below, so that the swap
+ * vector can be tested with small even values (e.g. 20) for ENTRIES_PER_PAGE.
+ */
 #define ENTRIES_PER_PAGE (PAGE_CACHE_SIZE/sizeof(unsigned long))
 #define ENTRIES_PER_PAGEPAGE ((unsigned long long)ENTRIES_PER_PAGE*ENTRIES_PER_PAGE)
-#define BLOCKS_PER_PAGE  (PAGE_CACHE_SIZE/512)
 
-#define SHMEM_MAX_INDEX  (SHMEM_NR_DIRECT + (ENTRIES_PER_PAGEPAGE/2) * (ENTRIES_PER_PAGE+1))
-#define SHMEM_MAX_BYTES  ((unsigned long long)SHMEM_MAX_INDEX << PAGE_CACHE_SHIFT)
+#define SHMSWP_MAX_INDEX (SHMEM_NR_DIRECT + (ENTRIES_PER_PAGEPAGE/2) * (ENTRIES_PER_PAGE+1))
+#define SHMSWP_MAX_BYTES (SHMSWP_MAX_INDEX << PAGE_CACHE_SHIFT)
 
+#define SHMEM_MAX_BYTES  min_t(unsigned long long, SHMSWP_MAX_BYTES, MAX_LFS_FILESIZE)
+#define SHMEM_MAX_INDEX  ((unsigned long)((SHMEM_MAX_BYTES+1) >> PAGE_CACHE_SHIFT))
+
+#define BLOCKS_PER_PAGE  (PAGE_CACHE_SIZE/512)
 #define VM_ACCT(size)    (PAGE_CACHE_ALIGN(size) >> PAGE_SHIFT)
 
 /* info->flags needs VM_flags to handle pagein/truncate races efficiently */
@@ -2581,7 +2596,7 @@ int shmem_unuse(swp_entry_t entry, struct page *page)
 #define shmem_get_inode(sb, mode, dev, flags)	ramfs_get_inode(sb, mode, dev)
 #define shmem_acct_size(flags, size)		0
 #define shmem_unacct_size(flags, size)		do {} while (0)
-#define SHMEM_MAX_BYTES				LLONG_MAX
+#define SHMEM_MAX_BYTES				MAX_LFS_FILESIZE
 
 #endif /* CONFIG_SHMEM */