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

To: Anthony PERARD <anthony.perard@xxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH] xen-mapcache: Fix rlimit set size.
From: Alexander Graf <agraf@xxxxxxx>
Date: Tue, 02 Aug 2011 16:50:30 +0200
Cc: Xen Devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, QEMU-devel <qemu-devel@xxxxxxxxxx>, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
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On 08/01/2011 09:26 PM, Anthony PERARD wrote:
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.

Not sure I understand. What are those 75MB?


Alex

Signed-off-by: Anthony PERARD<anthony.perard@xxxxxxxxxx>
---
  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) +


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