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Subject[PATCH] mm, arch: remove empty_bad_page*
Date
From: Michal Hocko <mhocko@suse.com>

empty_bad_page and empty_bad_pte_table seems to be a relict from old
days which is not used by any code for a long time. I have tried to find
when exactly but this is not really all that straightforward due to many
code movements - traces disappear around 2.4 times.

Anyway no code really references neither empty_bad_page nor
empty_bad_pte_table. We only allocate the storage which is not used by
anybody so remove them.

Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Rich Felker <dalias@libc.org>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: <uclinux-h8-devel@lists.sourceforge.jp>
Cc: <linux-mips@linux-mips.org>
Cc: <linux-sh@vger.kernel.org>
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
Hi,
Pasha Tatashin made me look closer at
include/linux/page-flags.h
* PG_reserved is set for special pages, which can never be swapped out. Some
* of them might not even exist (eg empty_bad_page)...
in http://lkml.kernel.org/r/691dba28-718c-e9a9-d006-88505eb5cd7e@oracle.com
because it was the first time I have heard about empty_bad_page. It
seems that this is no longer needed but there are some relicts in
arch code. Please note that I have no ways to test this other than
run it through my compile (cross arch) test battery and there were no
failures.

arch/frv/mm/init.c | 14 --------------
arch/h8300/mm/init.c | 13 -------------
arch/mips/include/asm/pgtable-64.h | 8 +-------
arch/mn10300/kernel/head.S | 8 --------
arch/sh/kernel/head_64.S | 8 --------
arch/um/kernel/mem.c | 3 ---
include/linux/page-flags.h | 2 +-
7 files changed, 2 insertions(+), 54 deletions(-)

diff --git a/arch/frv/mm/init.c b/arch/frv/mm/init.c
index 328f0a292316..cf464100e838 100644
--- a/arch/frv/mm/init.c
+++ b/arch/frv/mm/init.c
@@ -42,21 +42,9 @@
#undef DEBUG

/*
- * BAD_PAGE is the page that is used for page faults when linux
- * is out-of-memory. Older versions of linux just did a
- * do_exit(), but using this instead means there is less risk
- * for a process dying in kernel mode, possibly leaving a inode
- * unused etc..
- *
- * BAD_PAGETABLE is the accompanying page-table: it is initialized
- * to point to BAD_PAGE entries.
- *
* ZERO_PAGE is a special page that is used for zero-initialized
* data and COW.
*/
-static unsigned long empty_bad_page_table;
-static unsigned long empty_bad_page;
-
unsigned long empty_zero_page;
EXPORT_SYMBOL(empty_zero_page);

@@ -72,8 +60,6 @@ void __init paging_init(void)
unsigned long zones_size[MAX_NR_ZONES] = {0, };

/* allocate some pages for kernel housekeeping tasks */
- empty_bad_page_table = (unsigned long) alloc_bootmem_pages(PAGE_SIZE);
- empty_bad_page = (unsigned long) alloc_bootmem_pages(PAGE_SIZE);
empty_zero_page = (unsigned long) alloc_bootmem_pages(PAGE_SIZE);

memset((void *) empty_zero_page, 0, PAGE_SIZE);
diff --git a/arch/h8300/mm/init.c b/arch/h8300/mm/init.c
index 495a3d6b539b..85c51cf782a5 100644
--- a/arch/h8300/mm/init.c
+++ b/arch/h8300/mm/init.c
@@ -39,20 +39,9 @@
#include <asm/sections.h>

/*
- * BAD_PAGE is the page that is used for page faults when linux
- * is out-of-memory. Older versions of linux just did a
- * do_exit(), but using this instead means there is less risk
- * for a process dying in kernel mode, possibly leaving a inode
- * unused etc..
- *
- * BAD_PAGETABLE is the accompanying page-table: it is initialized
- * to point to BAD_PAGE entries.
- *
* ZERO_PAGE is a special page that is used for zero-initialized
* data and COW.
*/
-static unsigned long empty_bad_page_table;
-static unsigned long empty_bad_page;
unsigned long empty_zero_page;

/*
@@ -77,8 +66,6 @@ void __init paging_init(void)
* Initialize the bad page table and bad page to point
* to a couple of allocated pages.
*/
- empty_bad_page_table = (unsigned long)alloc_bootmem_pages(PAGE_SIZE);
- empty_bad_page = (unsigned long)alloc_bootmem_pages(PAGE_SIZE);
empty_zero_page = (unsigned long)alloc_bootmem_pages(PAGE_SIZE);
memset((void *)empty_zero_page, 0, PAGE_SIZE);

diff --git a/arch/mips/include/asm/pgtable-64.h b/arch/mips/include/asm/pgtable-64.h
index 67fe6dc5211c..0036ea0c7173 100644
--- a/arch/mips/include/asm/pgtable-64.h
+++ b/arch/mips/include/asm/pgtable-64.h
@@ -31,12 +31,7 @@
* tables. Each page table is also a single 4K page, giving 512 (==
* PTRS_PER_PTE) 8 byte ptes. Each pud entry is initialized to point to
* invalid_pmd_table, each pmd entry is initialized to point to
- * invalid_pte_table, each pte is initialized to 0. When memory is low,
- * and a pmd table or a page table allocation fails, empty_bad_pmd_table
- * and empty_bad_page_table is returned back to higher layer code, so
- * that the failure is recognized later on. Linux does not seem to
- * handle these failures very well though. The empty_bad_page_table has
- * invalid pte entries in it, to force page faults.
+ * invalid_pte_table, each pte is initialized to 0.
*
* Kernel mappings: kernel mappings are held in the swapper_pg_table.
* The layout is identical to userspace except it's indexed with the
@@ -175,7 +170,6 @@
printk("%s:%d: bad pgd %016lx.\n", __FILE__, __LINE__, pgd_val(e))

extern pte_t invalid_pte_table[PTRS_PER_PTE];
-extern pte_t empty_bad_page_table[PTRS_PER_PTE];

#ifndef __PAGETABLE_PUD_FOLDED
/*
diff --git a/arch/mn10300/kernel/head.S b/arch/mn10300/kernel/head.S
index 73e00fc78072..0b15f759e0d2 100644
--- a/arch/mn10300/kernel/head.S
+++ b/arch/mn10300/kernel/head.S
@@ -433,14 +433,6 @@ ENTRY(swapper_pg_dir)
ENTRY(empty_zero_page)
.space PAGE_SIZE

- .balign PAGE_SIZE
-ENTRY(empty_bad_page)
- .space PAGE_SIZE
-
- .balign PAGE_SIZE
-ENTRY(empty_bad_pte_table)
- .space PAGE_SIZE
-
.balign PAGE_SIZE
ENTRY(large_page_table)
.space PAGE_SIZE
diff --git a/arch/sh/kernel/head_64.S b/arch/sh/kernel/head_64.S
index defd851abefa..cca491397a28 100644
--- a/arch/sh/kernel/head_64.S
+++ b/arch/sh/kernel/head_64.S
@@ -101,14 +101,6 @@
mmu_pdtp_cache:
.space PAGE_SIZE, 0

- .global empty_bad_page
-empty_bad_page:
- .space PAGE_SIZE, 0
-
- .global empty_bad_pte_table
-empty_bad_pte_table:
- .space PAGE_SIZE, 0
-
.global fpu_in_use
fpu_in_use: .quad 0

diff --git a/arch/um/kernel/mem.c b/arch/um/kernel/mem.c
index e7437ec62710..3c0e470ea646 100644
--- a/arch/um/kernel/mem.c
+++ b/arch/um/kernel/mem.c
@@ -22,8 +22,6 @@
/* allocated in paging_init, zeroed in mem_init, and unchanged thereafter */
unsigned long *empty_zero_page = NULL;
EXPORT_SYMBOL(empty_zero_page);
-/* allocated in paging_init and unchanged thereafter */
-static unsigned long *empty_bad_page = NULL;

/*
* Initialized during boot, and readonly for initializing page tables
@@ -146,7 +144,6 @@ void __init paging_init(void)
int i;

empty_zero_page = (unsigned long *) alloc_bootmem_low_pages(PAGE_SIZE);
- empty_bad_page = (unsigned long *) alloc_bootmem_low_pages(PAGE_SIZE);
for (i = 0; i < ARRAY_SIZE(zones_size); i++)
zones_size[i] = 0;

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index ba2d470d2d0a..048b763e939d 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -17,7 +17,7 @@
* Various page->flags bits:
*
* PG_reserved is set for special pages, which can never be swapped out. Some
- * of them might not even exist (eg empty_bad_page)...
+ * of them might not even exist...
*
* The PG_private bitflag is set on pagecache pages if they contain filesystem
* specific data (which is normally at page->private). It can be used by
--
2.14.2
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