2005-04-04 15:11:12

by Martin Hicks

Subject: [PATCH] meminfo: add Cached underflow check

Hi,

This patch was generated against 2.6.12-rc1

Working on some code lately I've been getting huge values
for "Cached". The cause is that get_page_cache_size() is an
approximate value, and for a sufficiently small returned value
of get_page_cache_size() the value underflows.

Signed-off-by: Martin Hicks <[email protected]>

proc_misc.c | 9 ++++++++-
1 files changed, 8 insertions(+), 1 deletion(-)

Index: linux-2.6.11.cached-limit/fs/proc/proc_misc.c
===================================================================
--- linux-2.6.11.cached-limit.orig/fs/proc/proc_misc.c 2005-03-31 11:36:46.000000000 -0800
+++ linux-2.6.11.cached-limit/fs/proc/proc_misc.c 2005-03-31 11:37:12.000000000 -0800
@@ -126,6 +126,7 @@ static int meminfo_read_proc(char *page,
unsigned long committed;
unsigned long allowed;
struct vmalloc_info vmi;
+ unsigned long cached;

get_page_state(&ps);
get_zone_counts(&active, &inactive, &free);
@@ -140,6 +141,12 @@ static int meminfo_read_proc(char *page,
allowed = ((totalram_pages - hugetlb_total_pages())
* sysctl_overcommit_ratio / 100) + total_swap_pages;

+ cached = get_page_cache_size();
+ if (total_swapcache_pages+i.bufferram < cached)
+ cached -= total_swapcache_pages + i.bufferram;
+ else
+ cached = 0;
+
get_vmalloc_info(&vmi);

/*
@@ -172,7 +179,7 @@ static int meminfo_read_proc(char *page,
K(i.totalram),
K(i.freeram),
K(i.bufferram),
- K(get_page_cache_size()-total_swapcache_pages-i.bufferram),
+ K(cached),
K(total_swapcache_pages),
K(active),
K(inactive),

2005-04-04 22:13:56

by Andrew Morton

Subject: Re: [PATCH] meminfo: add Cached underflow check

Martin Hicks <[email protected]> wrote:
>
> Working on some code lately I've been getting huge values
> for "Cached". The cause is that get_page_cache_size() is an
> approximate value, and for a sufficiently small returned value
> of get_page_cache_size() the value underflows.

OK..

I think I'd prefer to do it this way - it's simpler and the original patch
had a teeny race wrt changes in total_swapcache_pages.


diff -puN fs/proc/proc_misc.c~meminfo-add-cached-underflow-check fs/proc/proc_misc.c
--- 25/fs/proc/proc_misc.c~meminfo-add-cached-underflow-check Mon Apr 4 15:06:38 2005
+++ 25-akpm/fs/proc/proc_misc.c Mon Apr 4 15:10:24 2005
@@ -126,6 +126,7 @@ static int meminfo_read_proc(char *page,
unsigned long committed;
unsigned long allowed;
struct vmalloc_info vmi;
+ long cached;

get_page_state(&ps);
get_zone_counts(&active, &inactive, &free);
@@ -140,6 +141,10 @@ static int meminfo_read_proc(char *page,
allowed = ((totalram_pages - hugetlb_total_pages())
* sysctl_overcommit_ratio / 100) + total_swap_pages;

+ cached = get_page_cache_size() - total_swapcache_pages - i.bufferram;
+ if (cached < 0)
+ cached = 0;
+
get_vmalloc_info(&vmi);

/*
@@ -172,7 +177,7 @@ static int meminfo_read_proc(char *page,
K(i.totalram),
K(i.freeram),
K(i.bufferram),
- K(get_page_cache_size()-total_swapcache_pages-i.bufferram),
+ K(cached),
K(total_swapcache_pages),
K(active),
K(inactive),
_

2005-04-04 22:52:25

by Martin Hicks

Subject: Re: [PATCH] meminfo: add Cached underflow check

On Mon, Apr 04, 2005 at 03:10:49PM -0700, Andrew Morton wrote:
> Martin Hicks <[email protected]> wrote:
> >
> > Working on some code lately I've been getting huge values
> > for "Cached". The cause is that get_page_cache_size() is an
> > approximate value, and for a sufficiently small returned value
> > of get_page_cache_size() the value underflows.
>
> OK..
>
> I think I'd prefer to do it this way - it's simpler and the original patch
> had a teeny race wrt changes in total_swapcache_pages.

Fine by me.

mh

--
Martin Hicks || Silicon Graphics Inc. || [email protected]