[PATCH] meminfo: add Cached underflow check [Linux 2.6.12]

This Linux kernel change "[PATCH] meminfo: add Cached underflow check" is included in the Linux 2.6.12 release. This change is authored by Martin Hicks <mort [at] sgi.com> on Sat Apr 16 15:24:08 2005 -0700. The commit for this change in Linux stable tree is 4c4c402 (patch).

[PATCH] meminfo: add Cached underflow check

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 <mort@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

There are 7 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 fs/proc/proc_misc.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/proc/proc_misc.c b/fs/proc/proc_misc.c
index 1d75d6a..a60a3b3 100644
--- a/fs/proc/proc_misc.c
+++ b/fs/proc/proc_misc.c
@@ -126,6 +126,7 @@ static int meminfo_read_proc(char *page, char **start, off_t off,
    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, char **start, off_t off,
    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, char **start, off_t off,
        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),

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