Re: [PATCH 1/4] printk: Allocate kernel log buffer earlier

From: Mike Travis
Date: Mon Feb 28 2011 - 14:23:45 EST



Yinghai Lu wrote:
On 02/27/2011 04:15 AM, Ingo Molnar wrote:
* Ingo Molnar <mingo@xxxxxxx> wrote:

You could avoid all this ugly workaround of bootmem limitations by moving the allocation to memblock_alloc() and desupporting the log_buf_len= boot parameter on non-memblock architectures.
memblock_alloc() could return -ENOSYS on architectures that do not implement it - thus enabling such optional features without ugly #ifdef CONFIG_HAVE_MEMBLOCK conditionals.

Mike,

please check updated patch...

with the memblock change, you don't need to change acpi SRAT handling etc any more.

I had to debug a weird ACPI -> Node mapping last week and the
"improved" SRAT messages helped that considerably. It was
far easier to spot which Node didn't have the correct assignments.
I'd submit that patch even without needing fewer (like 512 lines
max instead of 4096 lines max) bytes in the log buffer.


new buffer will be near high mem under 4g.

Is this really that important? The patchset is ridiculously
simple as it is. Do I really need to spend more time on it?
I've already done 4 revisions of it and responded to all
objections.

I have a far more important patchset that I've been trying to
prepare that actually fixes broken code, instead of trying to
reduce a few thousand bytes in the log buffer.

And everyone that has experienced it here on our lab systems
say they like the improvements (even the ones that I had to
toss because of "that's not the way it was before" kind of
objections.)

Let's move on to far more important problems.

Thanks,
Mike



Thanks

Yinghai

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index a47fe00..69b8995 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -974,6 +974,11 @@ void __init setup_arch(char **cmdline_p)
memblock.current_limit = get_max_mapped();
/*
+ * Allocate bigger log buffer as early as possible
+ */
+ setup_log_buf();
+
+ /*
* NOTE: On x86-32, only from this point on, fixmaps are ready for use.
*/
diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index 62a10c2..c3ade22 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -2,6 +2,8 @@
#define _LINUX_MEMBLOCK_H
#ifdef __KERNEL__
+#define MEMBLOCK_ERROR 0
+
#ifdef CONFIG_HAVE_MEMBLOCK
/*
* Logical memory blocks.
@@ -20,7 +22,6 @@
#include <asm/memblock.h>
#define INIT_MEMBLOCK_REGIONS 128
-#define MEMBLOCK_ERROR 0
struct memblock_region {
phys_addr_t base;
@@ -160,6 +161,12 @@ static inline unsigned long memblock_region_reserved_end_pfn(const struct memblo
#define __initdata_memblock
#endif
+#else
+static inline phys_addr_t memblock_alloc(phys_addr_t size, phys_addr_t align)
+{
+ return MEMBLOCK_ERROR;
+}
+
#endif /* CONFIG_HAVE_MEMBLOCK */
#endif /* __KERNEL__ */
diff --git a/include/linux/printk.h b/include/linux/printk.h
index ee048e7..fd266a8 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -1,6 +1,8 @@
#ifndef __KERNEL_PRINTK__
#define __KERNEL_PRINTK__
+#include <linux/init.h>
+
extern const char linux_banner[];
extern const char linux_proc_banner[];
@@ -89,6 +91,8 @@ int no_printk(const char *fmt, ...)
extern asmlinkage __attribute__ ((format (printf, 1, 2)))
void early_printk(const char *fmt, ...);
+void __init setup_log_buf(void);
+
extern int printk_needs_cpu(int cpu);
extern void printk_tick(void);
diff --git a/init/main.c b/init/main.c
index 33c37c3..2085bb3 100644
--- a/init/main.c
+++ b/init/main.c
@@ -592,6 +592,7 @@ asmlinkage void __init start_kernel(void)
* These use large bootmem allocations and must precede
* kmem_cache_init()
*/
+ setup_log_buf();
pidhash_init();
vfs_caches_init_early();
sort_main_extable();
diff --git a/kernel/printk.c b/kernel/printk.c
index 3623152..14fa4d0 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -31,6 +31,7 @@
#include <linux/smp.h>
#include <linux/security.h>
#include <linux/bootmem.h>
+#include <linux/memblock.h>
#include <linux/syscalls.h>
#include <linux/kexec.h>
#include <linux/kdb.h>
@@ -162,46 +163,64 @@ void log_buf_kexec_setup(void)
}
#endif
+/* requested log_buf_len from kernel cmdline */
+static unsigned long __initdata new_log_buf_len;
+
+/* save requested log_buf_len since it's too early to process it */
static int __init log_buf_len_setup(char *str)
{
unsigned size = memparse(str, &str);
- unsigned long flags;
if (size)
size = roundup_pow_of_two(size);
- if (size > log_buf_len) {
- unsigned start, dest_idx, offset;
- char *new_log_buf;
+ if (size > log_buf_len)
+ new_log_buf_len = size;
- new_log_buf = alloc_bootmem(size);
- if (!new_log_buf) {
- printk(KERN_WARNING "log_buf_len: allocation failed\n");
- goto out;
- }
+ return 0;
+}
+early_param("log_buf_len", log_buf_len_setup);
- spin_lock_irqsave(&logbuf_lock, flags);
- log_buf_len = size;
- log_buf = new_log_buf;
-
- offset = start = min(con_start, log_start);
- dest_idx = 0;
- while (start != log_end) {
- log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
- start++;
- dest_idx++;
- }
- log_start -= offset;
- con_start -= offset;
- log_end -= offset;
- spin_unlock_irqrestore(&logbuf_lock, flags);
+void __init setup_log_buf(void)
+{
+ unsigned long flags;
+ unsigned start, dest_idx, offset;
+ char *new_log_buf;
+ phys_addr_t new_addr;
+ int free;
+
+ if (!new_log_buf_len)
+ return;
- printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
+ new_addr = memblock_alloc(new_log_buf_len, PAGE_SIZE);
+ if (new_addr != MEMBLOCK_ERROR)
+ new_log_buf = __va(new_addr);
+ else
+ new_log_buf = alloc_bootmem(new_log_buf_len);
+
+ spin_lock_irqsave(&logbuf_lock, flags);
+ log_buf_len = new_log_buf_len;
+ log_buf = new_log_buf;
+ new_log_buf_len = 0;
+ free = __LOG_BUF_LEN - log_end;
+
+ offset = start = min(con_start, log_start);
+ dest_idx = 0;
+ while (start != log_end) {
+ unsigned log_idx_mask = start & (__LOG_BUF_LEN - 1);
+
+ log_buf[dest_idx] = __log_buf[log_idx_mask];
+ start++;
+ dest_idx++;
}
-out:
- return 1;
-}
+ log_start -= offset;
+ con_start -= offset;
+ log_end -= offset;
+ spin_unlock_irqrestore(&logbuf_lock, flags);
-__setup("log_buf_len=", log_buf_len_setup);
+ pr_info("log_buf_len: %d\n", log_buf_len);
+ pr_info("early log buf free: %d(%d%%)\n",
+ free, (free * 100) / __LOG_BUF_LEN);
+}
#ifdef CONFIG_BOOT_PRINTK_DELAY


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/