[libvirt] [PATCH V2] qemu: Redefine the "unlimited" memory limits one more time

[Viktor Mihajlovski]

With kernel 3.18 (since commit 3e32cb2e0a12b6915056ff04601cf1bb9b44f967) the
"unlimited" value for cgroup memory limits has changed once again as its byte
value is now computed from a page counter.
The new "unlimited" value reported by the cgroup fs is therefore 2**51-1 pages
which is (VIR_DOMAIN_MEMORY_PARAM_UNLIMITED - 3072). This results e.g. in virsh
memtune displaying 9007199254740988 instead of unlimited for the limits.

This patch deals with the rounding issue by scaling the byte values reported
by the kernel and the PARAM_UNLIMITED value to page size and comparing those.

See also libvirt commit 231656bbeb9e4d3bedc44362784c35eee21cf0f4 for the
history for kernel 3.12 and before.

Signed-off-by: Viktor Mihajlovski <mihajlov at linux.vnet.ibm.com>
---
V2: Shifting the scaled kb values by 2 is of sufficient to account for
    4K pages. Friday night fallout, sorry for that.

 src/util/vircgroup.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/util/vircgroup.c b/src/util/vircgroup.c
index 24917e7..39c7de2 100644
--- a/src/util/vircgroup.c
+++ b/src/util/vircgroup.c
@@ -2542,7 +2542,7 @@ virCgroupGetMemoryHardLimit(virCgroupPtr group, unsigned long long *kb)
         goto cleanup;
 
     *kb = limit_in_bytes >> 10;
-    if (*kb > VIR_DOMAIN_MEMORY_PARAM_UNLIMITED)
+    if (*kb >> 2 >= VIR_DOMAIN_MEMORY_PARAM_UNLIMITED >> 2)
         *kb = VIR_DOMAIN_MEMORY_PARAM_UNLIMITED;
 
     ret = 0;
@@ -2604,7 +2604,7 @@ virCgroupGetMemorySoftLimit(virCgroupPtr group, unsigned long long *kb)
         goto cleanup;
 
     *kb = limit_in_bytes >> 10;
-    if (*kb > VIR_DOMAIN_MEMORY_PARAM_UNLIMITED)
+    if (*kb >> 2 >= VIR_DOMAIN_MEMORY_PARAM_UNLIMITED >> 2)
         *kb = VIR_DOMAIN_MEMORY_PARAM_UNLIMITED;
 
     ret = 0;
@@ -2666,7 +2666,7 @@ virCgroupGetMemSwapHardLimit(virCgroupPtr group, unsigned long long *kb)
         goto cleanup;
 
     *kb = limit_in_bytes >> 10;
-    if (*kb > VIR_DOMAIN_MEMORY_PARAM_UNLIMITED)
+    if (*kb >> 2 >= VIR_DOMAIN_MEMORY_PARAM_UNLIMITED >> 2)
         *kb = VIR_DOMAIN_MEMORY_PARAM_UNLIMITED;
 
     ret = 0;
-- 
1.9.1