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SubjectRe: [PATCH] percpu updates
On Sat, 04 May 2002 21:08:34 -0700
Andrew Morton <akpm@zip.com.au> wrote:

> And again, the numbers in /proc/meminfo are whacko:
>
> LowFree: 94724 kB
> SwapTotal: 4000040 kB
> SwapFree: 3999700 kB
> Dirty: 7232 kB
> Writeback: 4294967264 kB

Hmmm.... I've just applied the page-flags.h and page_alloc.c changes,
and I don't get this problem at all on my 2xi386 box on 2.5.13. I
even changed the name of "page_states" to "xpage_states" to find any
other references, and inserted a BUG() if it was being dereferenced
before per-cpu offsets were initialized.

Here's the diff: do you see problems when booting with this?
Rusty.
--
there are those who do and those who hang on and you don't see too
many doers quoting their contemporaries. -- Larry McVoy

diff -urN -I \$.*\$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.13/include/asm-generic/percpu.h working-2.5.13-page-per-cpu/include/asm-generic/percpu.h
--- linux-2.5.13/include/asm-generic/percpu.h Mon Apr 15 11:47:44 2002
+++ working-2.5.13-page-per-cpu/include/asm-generic/percpu.h Mon May 6 17:00:55 2002
@@ -5,6 +5,7 @@
#include <linux/compiler.h>

extern unsigned long __per_cpu_offset[NR_CPUS];
+extern int per_cpu_areas_done;

/* var is in discarded region: offset to particular copy we want */
#define per_cpu(var, cpu) (*RELOC_HIDE(&var, __per_cpu_offset[cpu]))
diff -urN -I \$.*\$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.13/include/linux/page-flags.h working-2.5.13-page-per-cpu/include/linux/page-flags.h
--- linux-2.5.13/include/linux/page-flags.h Mon May 6 11:12:01 2002
+++ working-2.5.13-page-per-cpu/include/linux/page-flags.h Mon May 6 17:01:43 2002
@@ -42,6 +42,8 @@
* address space...
*/

+#include <linux/percpu.h>
+
/*
* Don't use the *_dontuse flags. Use the macros. Otherwise you'll break
* locked- and dirty-page accounting. The top eight bits of page->flags are
@@ -69,18 +71,21 @@
/*
* Global page accounting. One instance per CPU.
*/
-extern struct page_state {
+struct page_state {
unsigned long nr_dirty;
unsigned long nr_writeback;
unsigned long nr_pagecache;
-} ____cacheline_aligned_in_smp page_states[NR_CPUS];
+};
+
+extern struct page_state __per_cpu_data xpage_states;

extern void get_page_state(struct page_state *ret);

#define mod_page_state(member, delta) \
do { \
preempt_disable(); \
- page_states[smp_processor_id()].member += (delta); \
+ if (!per_cpu_areas_done) BUG(); \
+ this_cpu(xpage_states).member += (delta); \
preempt_enable(); \
} while (0)

diff -urN -I \$.*\$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.13/init/main.c working-2.5.13-page-per-cpu/init/main.c
--- linux-2.5.13/init/main.c Wed May 1 15:09:29 2002
+++ working-2.5.13-page-per-cpu/init/main.c Mon May 6 16:55:22 2002
@@ -278,6 +278,7 @@

#ifdef __GENERIC_PER_CPU
unsigned long __per_cpu_offset[NR_CPUS];
+int per_cpu_areas_done;

static void __init setup_per_cpu_areas(void)
{
@@ -297,6 +298,7 @@
__per_cpu_offset[i] = ptr - __per_cpu_start;
memcpy(ptr, __per_cpu_start, size);
}
+ per_cpu_areas_done = 1;
}
#endif /* !__GENERIC_PER_CPU */

diff -urN -I \$.*\$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.13/mm/page_alloc.c working-2.5.13-page-per-cpu/mm/page_alloc.c
--- linux-2.5.13/mm/page_alloc.c Mon May 6 11:12:01 2002
+++ working-2.5.13-page-per-cpu/mm/page_alloc.c Mon May 6 17:02:20 2002
@@ -576,8 +576,8 @@
* The result is unavoidably approximate - it can change
* during and after execution of this function.
*/
-struct page_state page_states[NR_CPUS] __cacheline_aligned;
-EXPORT_SYMBOL(page_states);
+struct page_state __per_cpu_data xpage_states;
+EXPORT_SYMBOL(xpage_states);

void get_page_state(struct page_state *ret)
{
@@ -590,7 +590,7 @@
for (pcpu = 0; pcpu < smp_num_cpus; pcpu++) {
struct page_state *ps;

- ps = &page_states[cpu_logical_map(pcpu)];
+ ps = &per_cpu(xpage_states,cpu_logical_map(pcpu));
ret->nr_dirty += ps->nr_dirty;
ret->nr_writeback += ps->nr_writeback;
ret->nr_pagecache += ps->nr_pagecache;
-
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