[Qemu-devel] [PATCH] xen-mapcache: Fix rlimit set size.

[Anthony PERARD <anthony.perard@citrix.com>]

Previously, the address space soft limit was set mcache_max_size. So,
before the mcache_max_size was reached by the mapcache, QEMU was killed
for overuse of the virtual address space.

This patch fix that by setting the soft limit to mcache_max_size + 80MB.
I observed that QEMU use 75MB more than max_mcache_size after several
empirical tests.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
---
 xen-mapcache.c |   13 ++++++++++---
 1 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/xen-mapcache.c b/xen-mapcache.c
index 007136a..40212f7 100644
--- a/xen-mapcache.c
+++ b/xen-mapcache.c
@@ -40,6 +40,13 @@
 #endif
 #define MCACHE_BUCKET_SIZE (1UL << MCACHE_BUCKET_SHIFT)
 
+/* This is the size of the virtual address space reserve to QEMU that will not
+ * be use by MapCache.
+ * From empirical tests I observed that qemu use 75MB more than the
+ * max_mcache_size.
+ */
+#define NON_MCACHE_MEMORY_SIZE (80 * 1024 * 1024)
+
 #define mapcache_lock()   ((void)0)
 #define mapcache_unlock() ((void)0)
 
@@ -93,14 +100,14 @@ void xen_map_cache_init(void)
     mapcache->last_address_index = -1;
 
     getrlimit(RLIMIT_AS, &rlimit_as);
-    if (rlimit_as.rlim_max < MCACHE_MAX_SIZE) {
+    if (rlimit_as.rlim_max < MCACHE_MAX_SIZE + NON_MCACHE_MEMORY_SIZE) {
         rlimit_as.rlim_cur = rlimit_as.rlim_max;
     } else {
-        rlimit_as.rlim_cur = MCACHE_MAX_SIZE;
+        rlimit_as.rlim_cur = MCACHE_MAX_SIZE + NON_MCACHE_MEMORY_SIZE;
     }
 
     setrlimit(RLIMIT_AS, &rlimit_as);
-    mapcache->max_mcache_size = rlimit_as.rlim_cur;
+    mapcache->max_mcache_size = rlimit_as.rlim_cur - NON_MCACHE_MEMORY_SIZE;
 
     mapcache->nr_buckets =
         (((mapcache->max_mcache_size >> XC_PAGE_SHIFT) +
-- 
Anthony PERARD