diff -urN linux-bk/arch/i386/kernel/head.S linux/arch/i386/kernel/head.S
--- linux-bk/arch/i386/kernel/head.S 2004-04-01 10:17:01.000000000 -0500
+++ linux/arch/i386/kernel/head.S 2004-04-03 09:08:28.053518856 -0500
@@ -69,9 +69,22 @@
movl %eax,%gs
/*
+ * Clear BSS first so that there are no surprises...
+ * No need to cld as DF is already clear from cld above...
+ */
+ xorl %eax,%eax
+ movl $__bss_start - __PAGE_OFFSET,%edi
+ movl $__bss_stop - __PAGE_OFFSET,%ecx
+ subl %edi,%ecx
+ shrl $2,%ecx
+ rep ; stosl
+
+/*
* Initialize page tables. This creates a PDE and a set of page
* tables, which are located immediately beyond _end. The variable
* init_pg_tables_end is set up to point to the first "safe" location.
+ * Mappings are created both at virtual address 0 (identity mapping)
+ * and PAGE_OFFSET for up to _end+sizeof(page tables)+INIT_MAP_BEYOND_END.
*
* Warning: don't use %esi or the stack in this code. However, %esp
* can be used as a GPR if you really need it...
@@ -173,17 +186,6 @@
#endif /* CONFIG_SMP */
/*
- * Clear BSS first so that there are no surprises...
- * No need to cld as DF is already clear from cld above...
- */
- xorl %eax,%eax
- movl $__bss_start,%edi
- movl $__bss_stop,%ecx
- subl %edi,%ecx
- shrl $2,%ecx
- rep ; stosl
-
-/*
* start system 32-bit setup. We need to re-do some of the things done
* in 16-bit mode for the "real" operations.
*/
@@ -304,8 +306,6 @@
jmp L6 # main should never return here, but
# just in case, we know what happens.
-ready: .byte 0
-
/*
* We depend on ET to be correct. This checks for 287/387.
*/
@@ -353,13 +353,7 @@
jne rp_sidt
ret
-ENTRY(stack_start)
- .long init_thread_union+THREAD_SIZE
- .long __BOOT_DS
-
/* This is the default interrupt "handler" :-) */
-int_msg:
- .asciz "Unknown interrupt or fault at EIP %p %p %p\n"
ALIGN
ignore_int:
cld
@@ -386,6 +380,35 @@
iret
/*
+ * Real beginning of normal "text" segment
+ */
+ENTRY(stext)
+ENTRY(_stext)
+
+/*
+ * BSS section
+ */
+.section ".bss.page_aligned","w"
+ENTRY(swapper_pg_dir)
+ .fill 1024,4,0
+ENTRY(empty_zero_page)
+ .fill 4096,1,0
+
+/*
+ * This starts the data section.
+ */
+.data
+
+ENTRY(stack_start)
+ .long init_thread_union+THREAD_SIZE
+ .long __BOOT_DS
+
+ready: .byte 0
+
+int_msg:
+ .asciz "Unknown interrupt or fault at EIP %p %p %p\n"
+
+/*
* The IDT and GDT 'descriptors' are a strange 48-bit object
* only used by the lidt and lgdt instructions. They are not
* like usual segment descriptors - they consist of a 16-bit
@@ -417,39 +440,6 @@
.fill NR_CPUS-1,8,0 # space for the other GDT descriptors
/*
- * swapper_pg_dir is the main page directory, address 0x00101000
- *
- * This is initialized to create an identity-mapping at 0 (for bootup
- * purposes) and another mapping at virtual address PAGE_OFFSET. The
- * values put here should be all invalid (zero); the valid
- * entries are created dynamically at boot time.
- *
- * The code creates enough page tables to map 0-_end, the page tables
- * themselves, plus INIT_MAP_BEYOND_END bytes; see comment at beginning.
- */
-.org 0x1000
-ENTRY(swapper_pg_dir)
- .fill 1024,4,0
-
-.org 0x2000
-ENTRY(empty_zero_page)
- .fill 4096,1,0
-
-.org 0x3000
-/*
- * Real beginning of normal "text" segment
- */
-ENTRY(stext)
-ENTRY(_stext)
-
-/*
- * This starts the data section. Note that the above is all
- * in the text section because it has alignment requirements
- * that we cannot fulfill any other way.
- */
-.data
-
-/*
* The boot_gdt_table must mirror the equivalent in setup.S and is
* used only for booting.
*/
diff -urN linux-bk/arch/i386/kernel/vmlinux.lds.S linux/arch/i386/kernel/vmlinux.lds.S
--- linux-bk/arch/i386/kernel/vmlinux.lds.S 2004-04-01 10:17:01.000000000 -0500
+++ linux/arch/i386/kernel/vmlinux.lds.S 2004-04-02 09:25:14.000000000 -0500
@@ -105,7 +105,10 @@
/* freed after init ends here */
__bss_start = .; /* BSS */
- .bss : { *(.bss) }
+ .bss : {
+ *(.bss.page_aligned)
+ *(.bss)
+ }
. = ALIGN(4);
__bss_stop = .;
On Sat, Apr 03, 2004 at 09:32:07AM -0500, Brian Gerst wrote:
> - Move empty_zero_page and swapper_pg_dir to BSS. This requires that
> BSS is cleared earlier, but reclaims over 3k that was lost due to page
> alignment.
> - Move stack_start, ready, and int_msg, boot_gdt_descr, idt_descr, and
> cpu_gdt_descr to .data. They were interfering with disassembly while in
> .text.
Nice. Do you mean 3k here or 0x3000?
On a related note, I've been sitting on this patch which reorders the
bootstrap code so we can free most of it once we're up:
drop i386 bootstrap text
From: Zwane Mwaikambo <[email protected]>
Subject: [PATCH][2.6-tiny] free i386 bootstrap text
Shuffle the idt/gdt descriptors around so that we get a full page and then
free it.
Index: linux-2.6.1-rc1-tiny2/arch/i386/kernel/head.S
===================================================================
RCS file: /home/cvsroot/linux-2.6.1-rc1-tiny2/arch/i386/kernel/head.S,v
retrieving revision 1.1.1.1
diff -u -p -B -r1.1.1.1 head.S
tiny-mpm/arch/i386/kernel/head.S | 40 +++++++++++++++++++--------------------
tiny-mpm/arch/i386/mm/init.c | 8 +++++++
2 files changed, 28 insertions(+), 20 deletions(-)
diff -puN arch/i386/kernel/head.S~bootstrap-free arch/i386/kernel/head.S
--- tiny/arch/i386/kernel/head.S~bootstrap-free 2004-03-20 12:14:33.000000000 -0600
+++ tiny-mpm/arch/i386/kernel/head.S 2004-03-20 12:14:33.000000000 -0600
@@ -386,6 +386,26 @@ ignore_int:
iret
/*
+ * swapper_pg_dir is the main page directory, address 0x00101000
+ *
+ * This is initialized to create an identity-mapping at 0 (for bootup
+ * purposes) and another mapping at virtual address PAGE_OFFSET. The
+ * values put here should be all invalid (zero); the valid
+ * entries are created dynamically at boot time.
+ *
+ * The code creates enough page tables to map 0-_end, the page tables
+ * themselves, plus INIT_MAP_BEYOND_END bytes; see comment at beginning.
+ */
+.org 0x1000
+ENTRY(swapper_pg_dir)
+ .fill 1024,4,0
+
+.org 0x2000
+ENTRY(empty_zero_page)
+ .fill 4096,1,0
+
+.org 0x3000
+/*
* The IDT and GDT 'descriptors' are a strange 48-bit object
* only used by the lidt and lgdt instructions. They are not
* like usual segment descriptors - they consist of a 16-bit
@@ -417,26 +437,6 @@ cpu_gdt_descr:
.fill NR_CPUS-1,8,0 # space for the other GDT descriptors
/*
- * swapper_pg_dir is the main page directory, address 0x00101000
- *
- * This is initialized to create an identity-mapping at 0 (for bootup
- * purposes) and another mapping at virtual address PAGE_OFFSET. The
- * values put here should be all invalid (zero); the valid
- * entries are created dynamically at boot time.
- *
- * The code creates enough page tables to map 0-_end, the page tables
- * themselves, plus INIT_MAP_BEYOND_END bytes; see comment at beginning.
- */
-.org 0x1000
-ENTRY(swapper_pg_dir)
- .fill 1024,4,0
-
-.org 0x2000
-ENTRY(empty_zero_page)
- .fill 4096,1,0
-
-.org 0x3000
-/*
* Real beginning of normal "text" segment
*/
ENTRY(stext)
diff -puN arch/i386/mm/init.c~bootstrap-free arch/i386/mm/init.c
--- tiny/arch/i386/mm/init.c~bootstrap-free 2004-03-20 12:14:33.000000000 -0600
+++ tiny-mpm/arch/i386/mm/init.c 2004-03-20 12:14:33.000000000 -0600
@@ -586,6 +586,14 @@ void free_initmem(void)
free_page(addr);
totalram_pages++;
}
+
+ /* free early bootstrap code in head.S */
+ addr = (unsigned long)&_text;
+ ClearPageReserved(virt_to_page(addr));
+ set_page_count(virt_to_page(addr), 1);
+ free_page(addr);
+ totalram_pages++;
+
printk (KERN_INFO "Freeing unused kernel memory: %dk freed\n", (__init_end - __init_begin) >> 10);
}
_
--
Matt Mackall : http://www.selenic.com : Linux development and consulting
Matt Mackall wrote:
> On Sat, Apr 03, 2004 at 09:32:07AM -0500, Brian Gerst wrote:
>
>>- Move empty_zero_page and swapper_pg_dir to BSS. This requires that
>>BSS is cleared earlier, but reclaims over 3k that was lost due to page
>>alignment.
>>- Move stack_start, ready, and int_msg, boot_gdt_descr, idt_descr, and
>>cpu_gdt_descr to .data. They were interfering with disassembly while in
>>.text.
>
>
> Nice. Do you mean 3k here or 0x3000?
3 kilobytes apporiximately. Most of the first page was wasted because
swapper_pg_dir aligns to the start of the next page.
>
> On a related note, I've been sitting on this patch which reorders the
> bootstrap code so we can free most of it once we're up:
>
The bootstrap page tables can easily be reclaimed if large pages are
used, but the bootstrap code needs more care, especially with hotplug cpus.
--
Brian Gerst
On Sat, 3 Apr 2004, Brian Gerst wrote:
> > On a related note, I've been sitting on this patch which reorders the
> > bootstrap code so we can free most of it once we're up:
> >
>
> The bootstrap page tables can easily be reclaimed if large pages are
> used, but the bootstrap code needs more care, especially with hotplug cpus.
This would be fine for hotplug cpus as well, we never hit that path again.
Brian Gerst wrote:
> - Move empty_zero_page and swapper_pg_dir to BSS. This requires that
> BSS is cleared earlier, but reclaims over 3k that was lost due to page
> alignment.
> - Move stack_start, ready, and int_msg, boot_gdt_descr, idt_descr, and
> cpu_gdt_descr to .data. They were interfering with disassembly while in
> .text.
>
Interesting, two years ago in 2002, you sent a patch basically of the
same idea.
http://www.uwsg.iu.edu/hypermail/linux/kernel/0208.0/0850.html
--
Coywolf Qi Hunt
Admin of http://GreatCN.org and http://LoveCN.org
On Thu, 15 Apr 2004 22:14:19 +0800 Coywolf Qi Hunt wrote:
| Brian Gerst wrote:
|
| > - Move empty_zero_page and swapper_pg_dir to BSS. This requires that
| > BSS is cleared earlier, but reclaims over 3k that was lost due to page
| > alignment.
| > - Move stack_start, ready, and int_msg, boot_gdt_descr, idt_descr, and
| > cpu_gdt_descr to .data. They were interfering with disassembly while in
| > .text.
| >
|
| Interesting, two years ago in 2002, you sent a patch basically of the
| same idea.
|
| http://www.uwsg.iu.edu/hypermail/linux/kernel/0208.0/0850.html
and your point is??
--
~Randy
Followup to: <[email protected]>
By author: Brian Gerst <[email protected]>
In newsgroup: linux.dev.kernel
>
> - Move empty_zero_page and swapper_pg_dir to BSS. This requires that
> BSS is cleared earlier, but reclaims over 3k that was lost due to page
> alignment.
> - Move stack_start, ready, and int_msg, boot_gdt_descr, idt_descr, and
> cpu_gdt_descr to .data. They were interfering with disassembly while in
> .text.
>
Some of them should be in .rodata instead of .data.
.data should only be used for modifiable numbers.
All in all these patches are a good idea; I had the same thoughts when
I was doing the changes to the boot page tables, but didn't want to
change too much at once.
-hpa