Linus reported that glibc (rather stupidly) reads /proc/meminfo
for every sysinfo() call, which causes the Git build to use
a surprising amount of CPU time, mostly due to the overhead
of get_vmalloc_info() - which walks a long list to do its
statistics.
Modify Linus's jiffies based patch to use the newly introduced
vmap_info_changed flag instead: when we cache the vmalloc-info,
we clear the flag. If the flag gets re-set then we'll calculate
the information again.
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
mm/vmalloc.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index d21febaa557a..ef48e557df5a 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2702,7 +2702,7 @@ static int __init proc_vmalloc_init(void)
}
module_init(proc_vmalloc_init);
-void get_vmalloc_info(struct vmalloc_info *vmi)
+static void calc_vmalloc_info(struct vmalloc_info *vmi)
{
struct vmap_area *va;
unsigned long free_area_size;
@@ -2749,5 +2749,23 @@ void get_vmalloc_info(struct vmalloc_info *vmi)
out:
rcu_read_unlock();
}
-#endif
+void get_vmalloc_info(struct vmalloc_info *vmi)
+{
+ static struct vmalloc_info cached_info;
+
+ if (!vmap_info_changed) {
+ *vmi = cached_info;
+ return;
+ }
+
+ WRITE_ONCE(vmap_info_changed, 0);
+ barrier();
+
+ calc_vmalloc_info(vmi);
+
+ barrier();
+ cached_info = *vmi;
+}
+
+#endif
--
2.1.4
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