Messages in this thread | | | Date | Thu, 26 Jun 2008 16:49:02 +0200 | From | Nadia Derbey <> | Subject | Re: [PATCH -mm 1/3] sysv ipc: increase msgmnb default value wrt. the number of cpus |
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Andrew Morton wrote: > On Tue, 24 Jun 2008 11:34:53 +0200 > <Solofo.Ramangalahy@bull.net> wrote: > > >>From: Solofo Ramangalahy <Solofo.Ramangalahy@bull.net> >> >>Initialize msgmnb value to >>min(MSGMNB * num_online_cpus(), MSGMNB * MSG_CPU_SCALE) >>to increase the default value for larger machines. >> >>MSG_CPU_SCALE scaling factor is defined to be 4, as 16384 x 4 = 65536 >>is an already used and recommended value. >> >>The msgmni value is made dependant of msgmnb to keep the memory >>dedicated to message queues within the 1/MSG_MEM_SCALE of lowmem >>bound. >> >>Unlike msgmni, the value is not scaled (down) with respect to the >>number of ipc namespaces for simplicity. >> >>To disable recomputation when user explicitely set a value, >>we reuse the callback defined for msgmni. >> >>As msgmni and msgmnb are correlated, user settings of any of the two >>disable recomputation of both, for now. This is refined in a later >>patch. >> >>When a negative value is put in /proc/sys/kernel/msgmnb >>automatic recomputing is re-enabled. >> > > > Thanks for taking the time to describe this work so well. > > >>--- >> Documentation/sysctl/kernel.txt | 28 ++++++++++++++++++++++++++++ >> include/linux/msg.h | 6 ++++++ >> ipc/ipc_sysctl.c | 5 +++-- >> ipc/msg.c | 17 +++++++++++++---- >> 4 files changed, 50 insertions(+), 6 deletions(-) >> >>Index: b/ipc/msg.c >>=================================================================== >>--- a/ipc/msg.c >>+++ b/ipc/msg.c >>@@ -38,6 +38,7 @@ >> #include <linux/rwsem.h> >> #include <linux/nsproxy.h> >> #include <linux/ipc_namespace.h> >>+#include <linux/cpumask.h> >> >> #include <asm/current.h> >> #include <asm/uaccess.h> >>@@ -92,7 +93,7 @@ void recompute_msgmni(struct ipc_namespa >> >> si_meminfo(&i); >> allowed = (((i.totalram - i.totalhigh) / MSG_MEM_SCALE) * i.mem_unit) >>- / MSGMNB; >>+ / ns->msg_ctlmnb; >> nb_ns = atomic_read(&nr_ipc_ns); >> allowed /= nb_ns; >> >>@@ -108,11 +109,19 @@ void recompute_msgmni(struct ipc_namespa >> >> ns->msg_ctlmni = allowed; >> } >>+/* >>+ * Scale msgmnb with the number of online cpus, up to 4x MSGMNB. >>+ */ >>+void recompute_msgmnb(struct ipc_namespace *ns) >>+{ >>+ ns->msg_ctlmnb = >>+ min(MSGMNB * num_online_cpus(), MSGMNB * MSG_CPU_SCALE); >>+} >> >> void msg_init_ns(struct ipc_namespace *ns) >> { >> ns->msg_ctlmax = MSGMAX; >>- ns->msg_ctlmnb = MSGMNB; >>+ recompute_msgmnb(ns); >> >> recompute_msgmni(ns); >> >>@@ -132,8 +141,8 @@ void __init msg_init(void) >> { >> msg_init_ns(&init_ipc_ns); >> >>- printk(KERN_INFO "msgmni has been set to %d\n", >>- init_ipc_ns.msg_ctlmni); >>+ printk(KERN_INFO "msgmni has been set to %d, msgmnb to %d\n", >>+ init_ipc_ns.msg_ctlmni, init_ipc_ns.msg_ctlmnb); >> >> ipc_init_proc_interface("sysvipc/msg", >> " key msqid perms cbytes qnum lspid lrpid uid gid cuid cgid stime rtime ctime\n", >>Index: b/include/linux/msg.h >>=================================================================== >>--- a/include/linux/msg.h >>+++ b/include/linux/msg.h >>@@ -58,6 +58,12 @@ struct msginfo { >> * more than 16 GB : msgmni = 32K (IPCMNI) >> */ >> #define MSG_MEM_SCALE 32 >>+/* >>+ * Scaling factor to compute msgmnb: ns->msg_ctlmnb is between MSGMNB >>+ * and MSGMNB * MSG_CPU_SCALE. This leads to a max msgmnb value of >>+ * 65536 which is an already used and recommended value. >>+ */ >>+#define MSG_CPU_SCALE 4 >> >> #define MSGMNI 16 /* <= IPCMNI */ /* max # of msg queue identifiers */ >> #define MSGMAX 8192 /* <= INT_MAX */ /* max size of message (bytes) */ >>Index: b/ipc/ipc_sysctl.c >>=================================================================== >>--- a/ipc/ipc_sysctl.c >>+++ b/ipc/ipc_sysctl.c >>@@ -42,6 +42,7 @@ static void tunable_set_callback(int val >> * Re-enable automatic recomputing only if not already >> * enabled. >> */ >>+ recompute_msgmnb(current->nsproxy->ipc_ns); >> recompute_msgmni(current->nsproxy->ipc_ns); >> cond_register_ipcns_notifier(current->nsproxy->ipc_ns); >> } >>@@ -210,8 +211,8 @@ static struct ctl_table ipc_kern_table[] >> .data = &init_ipc_ns.msg_ctlmnb, >> .maxlen = sizeof (init_ipc_ns.msg_ctlmnb), >> .mode = 0644, >>- .proc_handler = proc_ipc_dointvec, >>- .strategy = sysctl_ipc_data, >>+ .proc_handler = proc_ipc_callback_dointvec, >>+ .strategy = sysctl_ipc_registered_data, >> }, >> { >> .ctl_name = KERN_SEM, >>Index: b/Documentation/sysctl/kernel.txt >>=================================================================== >>--- a/Documentation/sysctl/kernel.txt >>+++ b/Documentation/sysctl/kernel.txt >>@@ -179,6 +179,34 @@ kernel stack. >> >> ============================================================== >> >>+msgmnb >>+ >>+Maximum size in bytes (not in message count) of a single SystemV IPC >>+message queue (b stands for bytes). >>+ >>+This value is dynamic and depends on the online cpu count of the >>+machine (taking cpu hotplug into account). >>+ >>+Computed values are between MSGMNB and MSGMNB*MSG_CPU_SCALE #define >>+constants (currently [16384,65536]). >>+ >>+The exact value is automatically (re)computed, but: >>+. If the value is positioned from user space (via procfs or sysctl()), >>+ to a positive value then the automatic recomputation is >>+ disabled. This leaves control to user space. E.g. >>+ >>+ # echo 16384 > /proc/sys/kernel/msgmnb >>+ >>+. If the value is positioned from user space to a negative value, then >>+ the computation is reenabled. E.g. >>+ >>+ # echo -1 > /proc/sys/kernel/msgmnb >>+ >>+See recompute_msgmnb() function in ipc/ directory for details. >>+The value of msgmnb is coupled with the value of msgmni. >>+ > > > The magical positive-versus-negative number trick is a bit obscure, and > I don't think there's any precedent for it in the kernel ABI (which is > what this is). > > Is there anything we can do to reduce the unusualness of this > interface? Say, add a new /proc/sys/kernel/automatic-msgmnb which > contains the automatic scaling and leave /proc/sys/kernel/msgmnb > containing the manual scaling? Or something like that?
Well, I don't know if I well understood your proposal: is it 1 value in automatic-msgmnb and another one in msgmnb? I don't clearly see how this could work.
IMHO, we should keep /proc/sys/kernel/msgmnb as a way to externalize the current tunable value (whether it is automatically recomputed or not).
Also keep the current strategy: as soon as a value is written into that file, give up with the automatic recomputing.
And use the file you propose as a way to go back and forth between automatic recomputing and manual setting.
So the process would be the following: 1) kernel boots in "automatic recomputing mode" /proc/kernel/sys/msgmni contains whatever value has been computed /proc/kernel/sys/automatic-msgmnb contains "ON"
2) echo <val> > /proc/kernel/sys/msgmnb . sets msg_ctlmnb to <val> . de-activates automatic recomputing (i.e. if, say, a cpu disappears it won't be recompiuted anymore) . /proc/kernel/sys/automatic-msgmnb now contains "OFF"
Echoing "OFF" into /proc/kernel/sys/automatic-msgmnb would have the same effect (except that msg_ctlmnb's value would stay blocked at its current value)
3) echo "ON" > /proc/kernel/sys/automatic-msgmnb . recomputes msgmnb's value based on the current available resources . re-activates automatic recomputing for msgmnb.
Of course, all this should be applied to msgmni too. And may be this automatic-xxx file should be located under sysfs? --> create /sys/kernel/automatic directory and have 1 file per tunable to be scalled (who knows, may be we are adding other ones in th future?)
Now, may be this is what you actually proposed and I completely misunderstod it?
Regards, Nadia
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