a)
SysV can be abused to allocate locked kernel memory. For most systems, a
small limit doesn't make sense, see the discussion with regards to SHMMAX.
Therefore: Increase the sysv sem limits so that all known applications
will work with these defaults.
b)
With regards to the maximum supported:
Some of the specified hard limits are not correct anymore, therefore the
patch updates the documentation.
- SEMMNI must stay below IPCMNI, which is 32768.
As for SHMMAX: Stay a bit below this limit.
- SEMMSL was limited to 8k, to ensure that the kmalloc for the kernel array
was limited to 16 kB (order=2)
This doesn't apply anymore:
- the allocation size isn't sizeof(short)*nsems anymore.
- ipc_alloc falls back to vmalloc
- SEMOPM should stay below 1000, to limit the kmalloc in semtimedop() to an
order=1 allocation.
Therefore: Leave it at 500 (order=0 allocation).
Note:
If an administrator must limit the memory allocations, then he can set the
values as necessary.
Or he can disable sysv entirely (as e.g. done by Android).
Signed-off-by: Manfred Spraul <manf...@colorfullife.com>
---
include/uapi/linux/sem.h | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/include/uapi/linux/sem.h b/include/uapi/linux/sem.h
index 541fce0..dd73b90 100644
--- a/include/uapi/linux/sem.h
+++ b/include/uapi/linux/sem.h
@@ -63,10 +63,22 @@ struct seminfo {
int semaem;
};
-#define SEMMNI 128 /* <= IPCMNI max # of semaphore identifiers */
-#define SEMMSL 250 /* <= 8 000 max num of semaphores per id */
+/*
+ * SEMMNI, SEMMSL and SEMMNS are default values which can be
+ * modified by sysctl.
+ * The values has been chosen to be larger than necessary for any
+ * known configuration.
+ *
+ * SEMOPM should not be increased beyond 1000, otherwise there is the
+ * risk that semop()/semtimedop() fails due to kernel memory fragmentation when
+ * allocating the sop array.
+ */
+
+
+#define SEMMNI 32000 /* <= IPCMNI max # of semaphore identifiers */
+#define SEMMSL 32000 /* <= INT_MAX max num of semaphores per id */
#define SEMMNS (SEMMNI*SEMMSL) /* <= INT_MAX max # of semaphores in system */
-#define SEMOPM 32 /* <= 1 000 max num of ops per semop call */
+#define SEMOPM 500 /* <= 1 000 max num of ops per semop call */
#define SEMVMX 32767 /* <= 32767 semaphore maximum value */
#define SEMAEM SEMVMX /* adjust on exit max value */
--
1.9.3
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