This is a note to let you know that I've just added the patch titled
ipc,shm: introduce lockless functions to obtain the ipc object
to the 3.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
ipc-shm-introduce-lockless-functions-to-obtain-the-ipc-object.patch
and it can be found in the queue-3.11 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 8b8d52ac382b17a19906b930cd69e2edb0aca8ba Mon Sep 17 00:00:00 2001
From: Davidlohr Bueso <davidlohr.bueso@xxxxxx>
Date: Wed, 11 Sep 2013 14:26:15 -0700
Subject: ipc,shm: introduce lockless functions to obtain the ipc object
From: Davidlohr Bueso <davidlohr.bueso@xxxxxx>
commit 8b8d52ac382b17a19906b930cd69e2edb0aca8ba upstream.
This is the third and final patchset that deals with reducing the amount
of contention we impose on the ipc lock (kern_ipc_perm.lock). These
changes mostly deal with shared memory, previous work has already been
done for semaphores and message queues:
http://lkml.org/lkml/2013/3/20/546 (sems)
http://lkml.org/lkml/2013/5/15/584 (mqueues)
With these patches applied, a custom shm microbenchmark stressing shmctl
doing IPC_STAT with 4 threads a million times, reduces the execution
time by 50%. A similar run, this time with IPC_SET, reduces the
execution time from 3 mins and 35 secs to 27 seconds.
Patches 1-8: replaces blindly taking the ipc lock for a smarter
combination of rcu and ipc_obtain_object, only acquiring the spinlock
when updating.
Patch 9: renames the ids rw_mutex to rwsem, which is what it already was.
Patch 10: is a trivial mqueue leftover cleanup
Patch 11: adds a brief lock scheme description, requested by Andrew.
This patch:
Add shm_obtain_object() and shm_obtain_object_check(), which will allow us
to get the ipc object without acquiring the lock. Just as with other
forms of ipc, these functions are basically wrappers around
ipc_obtain_object*().
Signed-off-by: Davidlohr Bueso <davidlohr.bueso@xxxxxx>
Tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
ipc/shm.c | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -124,6 +124,26 @@ void __init shm_init (void)
IPC_SHM_IDS, sysvipc_shm_proc_show);
}
+static inline struct shmid_kernel *shm_obtain_object(struct ipc_namespace *ns, int id)
+{
+ struct kern_ipc_perm *ipcp = ipc_obtain_object(&shm_ids(ns), id);
+
+ if (IS_ERR(ipcp))
+ return ERR_CAST(ipcp);
+
+ return container_of(ipcp, struct shmid_kernel, shm_perm);
+}
+
+static inline struct shmid_kernel *shm_obtain_object_check(struct ipc_namespace *ns, int id)
+{
+ struct kern_ipc_perm *ipcp = ipc_obtain_object_check(&shm_ids(ns), id);
+
+ if (IS_ERR(ipcp))
+ return ERR_CAST(ipcp);
+
+ return container_of(ipcp, struct shmid_kernel, shm_perm);
+}
+
/*
* shm_lock_(check_) routines are called in the paths where the rw_mutex
* is not necessarily held.
Patches currently in stable-queue which might be from davidlohr.bueso@xxxxxx are
queue-3.11/ipc-shm-shorten-critical-region-in-shmctl_down.patch
queue-3.11/ipc-shm-introduce-lockless-functions-to-obtain-the-ipc-object.patch
queue-3.11/ipc-shm-shorten-critical-region-for-shmat.patch
queue-3.11/ipc-shm-shorten-critical-region-for-shmctl.patch
queue-3.11/ipc-shm-introduce-shmctl_nolock.patch
queue-3.11/ipc-drop-ipcctl_pre_down.patch
queue-3.11/ipc-shm-cleanup-do_shmat-pasta.patch
queue-3.11/ipc-shm-make-shmctl_nolock-lockless.patch
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