The patch titled
Subject: ipc: do cyclic id allocation with ipcmni_extend mode
has been added to the -mm tree. Its filename is
ipc-do-cyclic-id-allocation-with-ipcmni_extend-mode.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/ipc-do-cyclic-id-allocation-with-ipcmni_extend-mode.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/ipc-do-cyclic-id-allocation-with-ipcmni_extend-mode.patch
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From: Waiman Long <longman@xxxxxxxxxx>
Subject: ipc: do cyclic id allocation with ipcmni_extend mode
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.
Link: http://lkml.kernel.org/r/1551379645-819-4-git-send-email-longman@xxxxxxxxxx
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Davidlohr Bueso <dbueso@xxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: "Luis R. Rodriguez" <mcgrof@xxxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/admin-guide/kernel-parameters.txt | 5 ++++-
ipc/ipc_sysctl.c | 2 ++
ipc/util.c | 7 ++++++-
ipc/util.h | 2 ++
4 files changed, 14 insertions(+), 2 deletions(-)
--- a/Documentation/admin-guide/kernel-parameters.txt~ipc-do-cyclic-id-allocation-with-ipcmni_extend-mode
+++ a/Documentation/admin-guide/kernel-parameters.txt
@@ -1813,7 +1813,10 @@
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.
--- a/ipc/ipc_sysctl.c~ipc-do-cyclic-id-allocation-with-ipcmni_extend-mode
+++ a/ipc/ipc_sysctl.c
@@ -122,6 +122,7 @@ static int one = 1;
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 *s
{
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;
}
--- a/ipc/util.c~ipc-do-cyclic-id-allocation-with-ipcmni_extend-mode
+++ a/ipc/util.c
@@ -221,7 +221,12 @@ static inline int ipc_idr_alloc(struct i
*/
if (next_id < 0) { /* !CHECKPOINT_RESTORE or next_id is unset */
- 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);
+
if ((idx <= ids->last_idx) && (++ids->seq > IPCID_SEQ_MAX))
ids->seq = 0;
new->seq = ids->seq;
--- a/ipc/util.h~ipc-do-cyclic-id-allocation-with-ipcmni_extend-mode
+++ a/ipc/util.h
@@ -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 @@ extern int ipc_mni_shift;
#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 */
_
Patches currently in -mm which might be from longman@xxxxxxxxxx are
debugobjects-move-printk-out-of-db-lock-critical-sections.patch
include-linux-nodemaskh-use-nr_node_ids-not-max_numnodes-in-__nodemask_pr_numnodes.patch
ipc-allow-boot-time-extension-of-ipcmni-from-32k-to-16m.patch
ipc-conserve-sequence-numbers-in-ipcmni_extend-mode.patch
ipc-do-cyclic-id-allocation-with-ipcmni_extend-mode.patch
