From e843e7d2c88b7db107a86bd2c7145dc715c058f4 Mon Sep 17 00:00:00 2001 From: Manfred Spraul Date: Fri, 12 Dec 2014 16:58:14 -0800 Subject: ipc/sem.c: increase SEMMSL, SEMMNI, SEMOPM 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 Cc: Davidlohr Bueso Acked-by: Rafael Aquini Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/uapi/linux/sem.h | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) (limited to 'include/uapi/linux') diff --git a/include/uapi/linux/sem.h b/include/uapi/linux/sem.h index 541fce03b50c..dd73b908b2f3 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 */ -- cgit v1.2.3 From 0050ee059f7fc86b1df2527aaa14ed5dc72f9973 Mon Sep 17 00:00:00 2001 From: Manfred Spraul Date: Fri, 12 Dec 2014 16:58:17 -0800 Subject: ipc/msg: increase MSGMNI, remove scaling 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 MSGMNI to the maximum supported. And: If we ignore the risk of locking too much memory, then an automatic scaling of MSGMNI doesn't make sense. Therefore the logic can be removed. The code preserves auto_msgmni to avoid breaking any user space applications that expect that the value exists. Notes: 1) If an administrator must limit the memory allocations, then he can set MSGMNI as necessary. Or he can disable sysv entirely (as e.g. done by Android). 2) MSGMAX and MSGMNB are intentionally not increased, as these values are used to control latency vs. throughput: If MSGMNB is large, then msgsnd() just returns and more messages can be queued before a task switch to a task that calls msgrcv() is forced. [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Manfred Spraul Cc: Davidlohr Bueso Cc: Rafael Aquini Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/uapi/linux/msg.h | 28 ++++++++++++++++++++-------- 1 file changed, 20 insertions(+), 8 deletions(-) (limited to 'include/uapi/linux') diff --git a/include/uapi/linux/msg.h b/include/uapi/linux/msg.h index a70375526578..f51c8001dbe5 100644 --- a/include/uapi/linux/msg.h +++ b/include/uapi/linux/msg.h @@ -51,16 +51,28 @@ struct msginfo { }; /* - * Scaling factor to compute msgmni: - * the memory dedicated to msg queues (msgmni * msgmnb) should occupy - * at most 1/MSG_MEM_SCALE of the lowmem (see the formula in ipc/msg.c): - * up to 8MB : msgmni = 16 (MSGMNI) - * 4 GB : msgmni = 8K - * more than 16 GB : msgmni = 32K (IPCMNI) + * MSGMNI, MSGMAX and MSGMNB are default values which can be + * modified by sysctl. + * + * MSGMNI is the upper limit for the number of messages queues per + * namespace. + * It has been chosen to be as large possible without facilitating + * scenarios where userspace causes overflows when adjusting the limits via + * operations of the form retrieve current limit; add X; update limit". + * + * MSGMNB is the default size of a new message queue. Non-root tasks can + * decrease the size with msgctl(IPC_SET), root tasks + * (actually: CAP_SYS_RESOURCE) can both increase and decrease the queue + * size. The optimal value is application dependent. + * 16384 is used because it was always used (since 0.99.10) + * + * MAXMAX is the maximum size of an individual message, it's a global + * (per-namespace) limit that applies for all message queues. + * It's set to 1/2 of MSGMNB, to ensure that at least two messages fit into + * the queue. This is also an arbitrary choice (since 2.6.0). */ -#define MSG_MEM_SCALE 32 -#define MSGMNI 16 /* <= IPCMNI */ /* max # of msg queue identifiers */ +#define MSGMNI 32000 /* <= IPCMNI */ /* max # of msg queue identifiers */ #define MSGMAX 8192 /* <= INT_MAX */ /* max size of message (bytes) */ #define MSGMNB 16384 /* <= INT_MAX */ /* default max size of a message queue */ -- cgit v1.2.3