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Date: Fri, 13 Mar 2009 14:03:07 -0700
From: Yinghai Lu <yinghai@...nel.org>
To: Jeremy Fitzhardinge <jeremy@...p.org>
CC: "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
the arch/x86 maintainers <x86@...nel.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] x86: add brk allocator for very early allocations
Jeremy Fitzhardinge wrote:
> Yinghai Lu wrote:
>> Jeremy Fitzhardinge wrote:
>>
>>> Yinghai Lu wrote:
>>>
>>>> could have more explanation about the 1M size.
>>>> because initial_pg_tables will sit in it. please consider to add
>>>> something like
>>>>
>>>> in head_32.S
>>>>
>>>> LOW_PAGES = (KERNEL_IMAGE_SIZE + PAGE_SIZE_asm - 1)>>PAGE_SHIFT
>>>>
>>>> #if PTRS_PER_PMD > 1
>>>> PAGE_TABLE_SIZE = (LOW_PAGES / PTRS_PER_PMD) + PTRS_PER_PGD
>>>> #else
>>>> PAGE_TABLE_SIZE = (LOW_PAGES / PTRS_PER_PGD)
>>>> #endif
>>>> ALLOCATOR_SLOP = 4
>>>>
>>> OK, how does this look:
>>>
>>> The following changes since commit
>>> 21e8ba72daf5d7f0af33968f873499c85f96ccef:
>>> Jeremy Fitzhardinge (1):
>>> x86: use brk allocation for DMI
>>>
>>> are available in the git repository at:
>>>
>>> git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen.git
>>> push/x86/brk
>>>
>>> Jeremy Fitzhardinge (1):
>>> x86: allow extend_brk users to reserve brk space
>>>
>>> Yinghai Lu (1):
>>> x86-32: compute initial mapping size more accurately
>>>
>>> arch/x86/include/asm/page_32_types.h | 5 +++++
>>> arch/x86/include/asm/setup.h | 30
>>> ++++++++++++++++++++++++++++++
>>> arch/x86/kernel/head_32.S | 4 +++-
>>> arch/x86/kernel/setup.c | 2 ++
>>> arch/x86/kernel/vmlinux_32.lds.S | 4 +++-
>>> arch/x86/kernel/vmlinux_64.lds.S | 4 +++-
>>> 6 files changed, 46 insertions(+), 3 deletions(-)
>>>
>>> git diff 21e8ba72daf5d7f0af33968f873499c85f96ccef..push/x86/brk
>>> diff --git a/arch/x86/include/asm/page_32_types.h
>>> b/arch/x86/include/asm/page_32_types.h
>>> index f1e4a79..0f915ae 100644
>>> --- a/arch/x86/include/asm/page_32_types.h
>>> +++ b/arch/x86/include/asm/page_32_types.h
>>> @@ -39,6 +39,11 @@
>>> #define __VIRTUAL_MASK_SHIFT 32
>>> #endif /* CONFIG_X86_PAE */
>>>
>>> +/*
>>> + * Kernel image size is limited to 512 MB (see in
>>> arch/x86/kernel/head_32.S)
>>> + */
>>> +#define KERNEL_IMAGE_SIZE (512 * 1024 * 1024)
>>> +
>>> #ifndef __ASSEMBLY__
>>>
>>> /*
>>> diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
>>> index 366d366..61b126b 100644
>>> --- a/arch/x86/include/asm/setup.h
>>> +++ b/arch/x86/include/asm/setup.h
>>> @@ -104,6 +104,29 @@ extern struct boot_params boot_params;
>>> extern unsigned long _brk_end;
>>> void *extend_brk(size_t size, size_t align);
>>>
>>> +/*
>>> + * Reserve space in the brk section. The name must be unique within
>>> + * the file, and somewhat descriptive. The size is in bytes. Must be
>>> + * used at file scope.
>>> + *
>>> + * (This uses a temp function to wrap the asm so we can pass it the
>>> + * size parameter; otherwise we wouldn't be able to. We can't use a
>>> + * "section" attribute on a normal variable because it always ends up
>>> + * being @progbits, which ends up allocating space in the vmlinux
>>> + * executable.)
>>> + */
>>> +#define RESERVE_BRK(name,sz) \
>>> + static void __section(.discard) __used \
>>> + __brk_reservation_fn_##name##__(void) { \
>>> + asm volatile ( \
>>> + ".pushsection .brk_reservation,\"aw\",@nobits;" \
>>> + "__brk_reservation_" #name "__:" \
>>> + " 1:.skip %c0;" \
>>> + " .size __brk_reservation_" #name "__, . - 1b;" \
>>> + " .popsection" \
>>> + : : "i" (sz)); \
>>> + }
>>> +
>>> #ifdef __i386__
>>>
>>> void __init i386_start_kernel(void);
>>> @@ -115,6 +138,13 @@ void __init x86_64_start_reservations(char
>>> *real_mode_data);
>>>
>>> #endif /* __i386__ */
>>> #endif /* _SETUP */
>>> +#else
>>> +#define RESERVE_BRK(name,sz) \
>>> + .pushsection .brk_reservation,"aw",@nobits; \
>>> +__brk_reservation_##name##__: \
>>> +1: .skip sz; \
>>> + .size __brk_reservation_##name##__,.-1b; \
>>> + .popsection
>>> #endif /* __ASSEMBLY__ */
>>> #endif /* __KERNEL__ */
>>>
>>> diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
>>> index d243437..80dc05e 100644
>>> --- a/arch/x86/kernel/head_32.S
>>> +++ b/arch/x86/kernel/head_32.S
>>> @@ -54,7 +54,7 @@
>>> *
>>> * This should be a multiple of a page.
>>> */
>>> -LOW_PAGES = 1<<(32-PAGE_SHIFT_asm)
>>> +LOW_PAGES = (KERNEL_IMAGE_SIZE + PAGE_SIZE_asm - 1)>>PAGE_SHIFT
>>>
>>> /*
>>> * To preserve the DMA pool in PAGEALLOC kernels, we'll allocate
>>> @@ -75,6 +75,8 @@ ALLOCATOR_SLOP = 4
>>>
>>> INIT_MAP_BEYOND_END = BOOTBITMAP_SIZE + (PAGE_TABLE_SIZE +
>>> ALLOCATOR_SLOP)*PAGE_SIZE_asm
>>>
>>
>> no user for INIT_MAP_BEYOND_END any more.
>>
>
> There are several remaining references:
>
> : abulafia:pts/0; grep INIT_MAP_BEYOND_END arch/x86/kernel/head_32.S
> INIT_MAP_BEYOND_END = BOOTBITMAP_SIZE + (PAGE_TABLE_SIZE +
> ALLOCATOR_SLOP)*PAGE_SIZE_asm
> * and PAGE_OFFSET for up to _end+sizeof(page tables)+INIT_MAP_BEYOND_END.
> * End condition: we must map up to and including INIT_MAP_BEYOND_END
> leal (INIT_MAP_BEYOND_END+PTE_IDENT_ATTR)(%edi),%ebp
> * End condition: we must map up to and including INIT_MAP_BEYOND_END
> leal (INIT_MAP_BEYOND_END+PTE_IDENT_ATTR)(%edi),%ebp
>
> Are you saying they're redundant and should be removed?
please check attached ...
Impact: cleanup
Don't use ram after _end blindly for pagetables. aka init pages is before _end
put those pg table into .bss
v2: keep initial page table up to 512M only.
v4: put initial page tables just before _end
Signed-off-by: Yinghai Lu <yinghai@...nel.org>
---
arch/x86/include/asm/page_32_types.h | 5 +++
arch/x86/kernel/head32.c | 3 +
arch/x86/kernel/head_32.S | 55 ++++++++++++++---------------------
arch/x86/kernel/vmlinux_32.lds.S | 11 ++++++-
4 files changed, 40 insertions(+), 34 deletions(-)
Index: linux-2.6/arch/x86/kernel/head32.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/head32.c
+++ linux-2.6/arch/x86/kernel/head32.c
@@ -18,7 +18,8 @@ void __init i386_start_kernel(void)
{
reserve_trampoline_memory();
- reserve_early(__pa_symbol(&_text), __pa_symbol(&_end), "TEXT DATA BSS");
+ reserve_early(__pa_symbol(&_text), __pa_symbol(&__bss_stop),
+ "TEXT DATA BSS");
#ifdef CONFIG_BLK_DEV_INITRD
/* Reserve INITRD */
Index: linux-2.6/arch/x86/kernel/head_32.S
===================================================================
--- linux-2.6.orig/arch/x86/kernel/head_32.S
+++ linux-2.6/arch/x86/kernel/head_32.S
@@ -38,42 +38,30 @@
#define X86_VENDOR_ID new_cpu_data+CPUINFO_x86_vendor_id
/*
- * This is how much memory *in addition to the memory covered up to
- * and including _end* we need mapped initially.
- * We need:
- * - one bit for each possible page, but only in low memory, which means
- * 232/4096/8 = 128K worst case (4G/4G split.)
+ * This is how much memory for page table to and including _end
+ * we need mapped initially.
* - enough space to map all low memory, which means
- * (232/4096) / 1024 pages (worst case, non PAE)
- * (232/4096) / 512 + 4 pages (worst case for PAE)
- * - a few pages for allocator use before the kernel pagetable has
- * been set up
+ * (KERNEL_IMAGE_SIZE/4096) / 1024 pages (worst case, non PAE)
+ * (KERNEL_IMAGE_SIZE/4096) / 512 + 4 pages (worst case for PAE)
*
* Modulo rounding, each megabyte assigned here requires a kilobyte of
* memory, which is currently unreclaimed.
*
* This should be a multiple of a page.
+ *
+ * KERNEL_IMAGE_SIZE should be greater than pa(_end)
+ * and small than max_low_pfn, otherwise will waste some page table entries
*/
-LOW_PAGES = 1<<(32-PAGE_SHIFT_asm)
-
-/*
- * To preserve the DMA pool in PAGEALLOC kernels, we'll allocate
- * pagetables from above the 16MB DMA limit, so we'll have to set
- * up pagetables 16MB more (worst-case):
- */
-#if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_KMEMCHECK)
-LOW_PAGES = LOW_PAGES + 0x1000000
-#endif
+LOW_PAGES = (KERNEL_IMAGE_SIZE + PAGE_SIZE_asm - 1)>>PAGE_SHIFT
#if PTRS_PER_PMD > 1
PAGE_TABLE_SIZE = (LOW_PAGES / PTRS_PER_PMD) + PTRS_PER_PGD
#else
PAGE_TABLE_SIZE = (LOW_PAGES / PTRS_PER_PGD)
#endif
-BOOTBITMAP_SIZE = LOW_PAGES / 8
ALLOCATOR_SLOP = 4
-INIT_MAP_BEYOND_END = BOOTBITMAP_SIZE + (PAGE_TABLE_SIZE + ALLOCATOR_SLOP)*PAGE_SIZE_asm
+INIT_MAP_SIZE = (PAGE_TABLE_SIZE + ALLOCATOR_SLOP) * PAGE_SIZE_asm
/*
* 32-bit kernel entrypoint; only used by the boot CPU. On entry,
@@ -166,10 +154,9 @@ num_subarch_entries = (. - subarch_entri
/*
* 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.
+ * tables, which are located immediately beyond _end.
* Mappings are created both at virtual address 0 (identity mapping)
- * and PAGE_OFFSET for up to _end+sizeof(page tables)+INIT_MAP_BEYOND_END.
+ * and PAGE_OFFSET for up to _end
*
* Note that the stack is not yet set up!
*/
@@ -209,14 +196,14 @@ default_entry:
loop 11b
/*
- * End condition: we must map up to and including INIT_MAP_BEYOND_END
- * bytes beyond the end of our own page tables.
+ * End condition: we must map up to the end.
*/
- leal (INIT_MAP_BEYOND_END+PTE_IDENT_ATTR)(%edi),%ebp
+ movl $pa(_end), %ebp
+ addl PTE_IDENT_ATTR, %ebp
cmpl %ebp,%eax
jb 10b
1:
- movl %edi,pa(init_pg_tables_end)
+ movl %edi, pa(init_pg_tables_end)
shrl $12, %eax
movl %eax, pa(max_pfn_mapped)
@@ -242,14 +229,14 @@ page_pde_offset = (__PAGE_OFFSET >> 20);
addl $0x1000,%eax
loop 11b
/*
- * End condition: we must map up to and including INIT_MAP_BEYOND_END
- * bytes beyond the end of our own page tables; the +0x007 is
+ * End condition: we must map up to end, the +0x007 is
* the attribute bits
*/
- leal (INIT_MAP_BEYOND_END+PTE_IDENT_ATTR)(%edi),%ebp
+ movl $pa(_end), %ebp
+ addl PTE_IDENT_ATTR, %ebp
cmpl %ebp,%eax
jb 10b
- movl %edi,pa(init_pg_tables_end)
+ movl %edi, pa(init_pg_tables_end)
shrl $12, %eax
movl %eax, pa(max_pfn_mapped)
@@ -636,6 +623,10 @@ swapper_pg_fixmap:
.fill 1024,4,0
ENTRY(empty_zero_page)
.fill 4096,1,0
+
+.section ".bss.extra_page_aligned","wa"
+ .align PAGE_SIZE_asm
+ .fill INIT_MAP_SIZE,1,0
/*
* This starts the data section.
*/
Index: linux-2.6/arch/x86/kernel/vmlinux_32.lds.S
===================================================================
--- linux-2.6.orig/arch/x86/kernel/vmlinux_32.lds.S
+++ linux-2.6/arch/x86/kernel/vmlinux_32.lds.S
@@ -189,10 +189,13 @@ SECTIONS
*(.bss)
. = ALIGN(4);
__bss_stop = .;
- _end = . ;
+ /* extra_page_aligned must be last one before end*/
/* This is where the kernel creates the early boot page tables */
. = ALIGN(PAGE_SIZE);
pg0 = . ;
+ *(.bss.extra_page_aligned)
+ . = ALIGN(8);
+ _end = . ;
}
/* Sections to be discarded */
@@ -205,6 +208,12 @@ SECTIONS
DWARF_DEBUG
}
+/*
+ * Build-time check on the image size:
+ */
+ASSERT((_end - LOAD_OFFSET <= KERNEL_IMAGE_SIZE),
+ "kernel image bigger than KERNEL_IMAGE_SIZE")
+
#ifdef CONFIG_KEXEC
/* Link time checks */
#include <asm/kexec.h>
Index: linux-2.6/arch/x86/include/asm/page_32_types.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/page_32_types.h
+++ linux-2.6/arch/x86/include/asm/page_32_types.h
@@ -39,6 +39,11 @@
#define __VIRTUAL_MASK_SHIFT 32
#endif /* CONFIG_X86_PAE */
+/*
+ * Kernel image size is limited to 512 MB (see in arch/x86/kernel/head_32.S)
+ */
+#define KERNEL_IMAGE_SIZE (512 * 1024 * 1024)
+
#ifndef __ASSEMBLY__
/*
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