lkml.org 
[lkml]   [2009]   [Feb]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH RFC] x86: add brk allocation for very, very early allocations
[
I'd like to add a mechanism like this so I can dynamically allocate some
Xen-related structures, rather than statically allocating them in the bss,
both so that Xen has less overhead when it isn't being used, and so I can
scale better to things like memory size.

I think this is more widely useful; it would supplant dmi_alloc_data[], for
example, and I'm sure there's other cases.

This is fundimentally the same as head_32.S's extension of the bss to build
the initial kernel mapping, but 64-bit doesn't currently do anything analogous
to this.

Unfortunately when I use this code as-is I'm getting crashes when the slab
allocator starts up. I think this is all correct, but I'm wondering if
there's something I'm overlooking which is broken in principle.

So, what am I missing?

Thanks,
J
]


Add a brk()-like allocator which effectively extends the bss
in order to allow very early code to do dynamic allocations.
This is better than using statically allocated arrays for
data in subsystems which may never get used.

The amount of space available depends on how much the initial
kernel mappings have covered, and so is fairly limited.

Not-Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
index 66801cb..e6b754b 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -99,6 +99,11 @@ extern struct boot_params boot_params;
*/
#define LOWMEMSIZE() (0x9f000)

+/* exceedingly early brk-like allocator */
+extern unsigned long _brk_start, _brk_end;
+void init_brk(unsigned long start);
+void *extend_brk(size_t size, size_t align);
+
#ifdef __i386__

void __init i386_start_kernel(void);
diff --git a/arch/x86/kernel/head32.c b/arch/x86/kernel/head32.c
index ac108d1..fa9ae31 100644
--- a/arch/x86/kernel/head32.c
+++ b/arch/x86/kernel/head32.c
@@ -34,6 +34,8 @@ void __init i386_start_kernel(void)

reserve_ebda_region();

+ init_brk((unsigned long)__va(init_pg_tables_end));
+
/*
* At this point everything still needed from the boot loader
* or BIOS or kernel text should be early reserved or marked not
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index f5b2722..4b29802 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -91,6 +91,8 @@ void __init x86_64_start_kernel(char * real_mode_data)
if (console_loglevel == 10)
early_printk("Kernel alive\n");

+ init_brk((unsigned long)&_end);
+
x86_64_start_reservations(real_mode_data);
}

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 0d051b4..8899cfa 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -113,6 +113,7 @@
#endif

unsigned int boot_cpu_id __read_mostly;
+__initdata unsigned long _brk_start, _brk_end;

#ifdef CONFIG_X86_64
int default_cpu_present_to_apicid(int mps_cpu)
@@ -335,6 +336,26 @@ static void __init relocate_initrd(void)
}
#endif

+void __init init_brk(unsigned long brk)
+{
+ _brk_start = _brk_end = brk;
+}
+
+void * __init extend_brk(size_t size, size_t align)
+{
+ size_t mask = align - 1;
+ void *ret;
+
+ BUG_ON(align & mask);
+
+ _brk_end = (_brk_end + mask) & ~mask;
+
+ ret = (void *)_brk_end;
+ _brk_end += size;
+
+ return ret;
+}
+
static void __init reserve_initrd(void)
{
u64 ramdisk_image = boot_params.hdr.ramdisk_image;
@@ -727,11 +748,7 @@ void __init setup_arch(char **cmdline_p)
init_mm.start_code = (unsigned long) _text;
init_mm.end_code = (unsigned long) _etext;
init_mm.end_data = (unsigned long) _edata;
-#ifdef CONFIG_X86_32
- init_mm.brk = init_pg_tables_end + PAGE_OFFSET;
-#else
- init_mm.brk = (unsigned long) &_end;
-#endif
+ init_mm.brk = _brk_end;

code_resource.start = virt_to_phys(_text);
code_resource.end = virt_to_phys(_etext)-1;
@@ -897,6 +914,9 @@ void __init setup_arch(char **cmdline_p)
acpi_numa_init();
#endif

+ if (_brk_end > _brk_start)
+ reserve_early(__pa(_brk_start), __pa(_brk_end), "BRK");
+
initmem_init(0, max_pfn);

#ifdef CONFIG_ACPI_SLEEP
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index dd5df65..4222ed6 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -16,6 +16,7 @@
#include <asm/processor.h>
#include <asm/tlbflush.h>
#include <asm/sections.h>
+#include <asm/setup.h>
#include <asm/uaccess.h>
#include <asm/pgalloc.h>
#include <asm/proto.h>
@@ -95,7 +96,7 @@ static inline unsigned long highmap_start_pfn(void)

static inline unsigned long highmap_end_pfn(void)
{
- return __pa(roundup((unsigned long)_end, PMD_SIZE)) >> PAGE_SHIFT;
+ return __pa(roundup(_brk_end, PMD_SIZE)) >> PAGE_SHIFT;
}

#endif
@@ -707,7 +708,7 @@ static int cpa_process_alias(struct cpa_data *cpa)
* No need to redo, when the primary call touched the high
* mapping already:
*/
- if (within(vaddr, (unsigned long) _text, (unsigned long) _end))
+ if (within(vaddr, (unsigned long) _text, _brk_end))
return 0;

/*
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 1815b8a..a3cc9ff 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -975,6 +975,9 @@ asmlinkage void __init xen_start_kernel(void)

init_mm.pgd = pgd;

+ /* Set up very early brk allocator after Xen pagetables */
+ init_brk(xen_start_info->pt_base + xen_start_info->nr_pt_frames * PAGE_SIZE);
+
/* keep using Xen gdt for now; no urgent need to change it */

pv_info.kernel_rpl = 1;



\
 
 \ /
  Last update: 2009-02-27 19:01    [W:0.102 / U:0.856 seconds]
©2003-2014 Jasper Spaans. Advertise on this site