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meminfo: add Cached underflow check

PATCH In review Martin Hicks 2 participants 3 messages Apr 4, 2005 Proc filesystem

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Martin Hicks

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#0 lore raw

PATCH 1/1 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(-)
fs/proc/proc_misc.c +8 -1
Index: linux-2.6.11.cached-limit/fs/proc/proc_misc.c
===================================================================
@@ -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),
#1 lore raw
Quoted 5 lines · Martin Hicks

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.

fs/proc/proc_misc.c renamed from fs/proc/proc_misc.c~meminfo-add-cached-underflow-check +6 -1
diff -puN fs/proc/proc_misc.c~meminfo-add-cached-underflow-check fs/proc/proc_misc.c
@@ -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),

_

author
#2 lore raw
Quoted 11 lines · Andrew Morton
Quoted 5 lines · Martin Hicks

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

Signature · 1 line
Martin Hicks   ||   Silicon Graphics Inc.   ||   [email protected]