@@ -1800,7 +1800,10 @@
See Documentation/filesystems/nfs/nfsroot.txt.
ipcmni_extend [KNL] Extend the maximum number of unique System V
- IPC identifiers from 32,768 to 16,777,216.
+ IPC identifiers from 32,768 to 16,777,216. Also do
+ cyclical identifier allocation through the entire
+ 24-bit identifier space to reduce the chance of
+ identifier reuse.
irqaffinity= [SMP] Set the default irq affinity mask
The argument is a cpu list, as described above.
@@ -122,6 +122,7 @@ static int proc_ipc_sem_dointvec(struct ctl_table *table, int write,
static int int_max = INT_MAX;
int ipc_mni = IPCMNI;
int ipc_mni_shift = IPCMNI_SHIFT;
+bool ipc_mni_extended;
static struct ctl_table ipc_kern_table[] = {
{
@@ -252,6 +253,7 @@ static int __init ipc_mni_extend(char *str)
{
ipc_mni = IPCMNI_EXTEND;
ipc_mni_shift = IPCMNI_EXTEND_SHIFT;
+ ipc_mni_extended = true;
pr_info("IPCMNI extended to %d.\n", ipc_mni);
return 0;
}
@@ -228,7 +228,11 @@ static inline int ipc_idr_alloc(struct ipc_ids *ids, struct kern_ipc_perm *new)
ids->deleted = false;
}
new->seq = ids->seq;
- idx = idr_alloc(&ids->ipcs_idr, new, 0, 0, GFP_NOWAIT);
+ if (ipc_mni_extended)
+ idx = idr_alloc_cyclic(&ids->ipcs_idr, new, 0, ipc_mni,
+ GFP_NOWAIT);
+ else
+ idx = idr_alloc(&ids->ipcs_idr, new, 0, 0, GFP_NOWAIT);
} else {
new->seq = ipcid_to_seqx(next_id);
idx = idr_alloc(&ids->ipcs_idr, new, ipcid_to_idx(next_id),
@@ -33,6 +33,7 @@
#ifdef CONFIG_SYSVIPC_SYSCTL
extern int ipc_mni;
extern int ipc_mni_shift;
+extern bool ipc_mni_extended;
#define IPCMNI_SEQ_SHIFT ipc_mni_shift
#define IPCMNI_IDX_MASK ((1 << ipc_mni_shift) - 1)
@@ -40,6 +41,7 @@
#else /* CONFIG_SYSVIPC_SYSCTL */
#define ipc_mni IPCMNI
+#define ipc_mni_extended false
#define IPCMNI_SEQ_SHIFT IPCMNI_SHIFT
#define IPCMNI_IDX_MASK ((1 << IPCMNI_SHIFT) - 1)
#endif /* CONFIG_SYSVIPC_SYSCTL */
For ipcmni_extend mode, the sequence number space is only 7 bits. So the chance of id reuse is relatively high compared with the non-extended mode. To alleviate this id reuse problem, the id allocation will be done cyclically to cycle through all the 24-bit id space before wrapping around when in ipcmni_extend mode. This may cause the use of more memory in term of the number of xa_nodes allocated as well as potentially more cachelines used as the xa_nodes may be spread more sparsely in this case. There is probably a slight memory and performance cost in doing cyclic id allocation. For applications that really need more than 32k unique IPC identifiers, this is a small price to pay to avoid the id reuse problem. As a result, the chance of id reuse should be even smaller in the ipcmni_extend mode. For users who worry about id reuse, they can turn on ipcmni_extend mode, even if they don't need more than 32k IPC identifiers. Signed-off-by: Waiman Long <longman@redhat.com> --- Documentation/admin-guide/kernel-parameters.txt | 5 ++++- ipc/ipc_sysctl.c | 2 ++ ipc/util.c | 6 +++++- ipc/util.h | 2 ++ 4 files changed, 13 insertions(+), 2 deletions(-)