Re: [GIT PULL] x86: add brk allocator for very early allocations
From: Jeremy Fitzhardinge
Date: Fri Mar 13 2009 - 16:27:44 EST
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?
could add
/*
* Build-time check on the image size:
*/
ASSERT((_end - LOAD_OFFSET <= KERNEL_IMAGE_SIZE),
"kernel image bigger than KERNEL_IMAGE_SIZE")
for 32bit
I guess we could, but it doesn't seem very urgent.
J
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