Re: [Patch 7/8] mqueue: separate mqueue default value from maximum value v2

["Serge E. Hallyn" <serge@hallyn.com>]

Quoting Doug Ledford (dledford@redhat.com):
> From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> 
> commit b231cca438 (message queues: increase range limits)
> changed mqueue default value when attr parameter is specified NULL
> from hard coded value to fs.mqueue.{msg,msgsize}_max sysctl value.
> 
> This made large side effect. When user need to use two mqueue
> applications 1) using !NULL attr parameter and it require big
> message size and 2) using NULL attr parameter and only need small
> size message, app (1) require to raise fs.mqueue.msgsize_max and
> app (2) consume large memory size even though it doesn't need.
> 
> Doug Ledford propsed to switch back it to static hard coded value.
> However it also has a compatibility problem. Some applications might
> started depend on the default value is tunable.
> 
> The solution is to separate default value from maximum value.
> 
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> Acked-by: Doug Ledford <dledford@redhat.com>
> Acked-by: Joe Korty <joe.korty@ccur.com>
> Cc: Amerigo Wang <amwang@redhat.com>
> Cc: Serge E. Hallyn <serue@us.ibm.com>

Seems reasonable.  Thanks.

Acked-by: Serge E. Hallyn <serge.hallyn@canonical.com>

> Cc: Jiri Slaby <jslaby@suse.cz>
> 
> v1->v2: Slightly modified because msgutil.c no longer needs mq
>   namespace initialization
> 
> Signed-off-by (v2): Doug Ledford <dledford@redhat.com>
> ---
>  Documentation/sysctl/fs.txt   |    7 +++++++
>  include/linux/ipc_namespace.h |    2 ++
>  ipc/mq_sysctl.c               |   18 ++++++++++++++++++
>  ipc/mqueue.c                  |    9 ++++++---
>  4 files changed, 33 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/sysctl/fs.txt b/Documentation/sysctl/fs.txt
> index 88fd7f5..13d6166 100644
> --- a/Documentation/sysctl/fs.txt
> +++ b/Documentation/sysctl/fs.txt
> @@ -225,6 +225,13 @@ a queue must be less or equal then msg_max.
>  maximum  message size value (it is every  message queue's attribute set during
>  its creation).
>  
> +/proc/sys/fs/mqueue/msg_default is  a read/write  file for setting/getting the
> +default number of messages in a queue value if attr parameter of mq_open(2) is
> +NULL. If it exceed msg_max, the default value is initialized msg_max.
> +
> +/proc/sys/fs/mqueue/msgsize_default is a read/write file for setting/getting
> +the default message size value if attr parameter of mq_open(2) is NULL. If it
> +exceed msgsize_max, the default value is initialized msgsize_max.
>  
>  4. /proc/sys/fs/epoll - Configuration options for the epoll interface
>  --------------------------------------------------------
> diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h
> index 2488535..5499c92 100644
> --- a/include/linux/ipc_namespace.h
> +++ b/include/linux/ipc_namespace.h
> @@ -62,6 +62,8 @@ struct ipc_namespace {
>  	unsigned int    mq_queues_max;   /* initialized to DFLT_QUEUESMAX */
>  	unsigned int    mq_msg_max;      /* initialized to DFLT_MSGMAX */
>  	unsigned int    mq_msgsize_max;  /* initialized to DFLT_MSGSIZEMAX */
> +	unsigned int    mq_msg_default;
> +	unsigned int    mq_msgsize_default;

Mention here what they are initialized to, for completeness?

>  
>  	/* user_ns which owns the ipc ns */
>  	struct user_namespace *user_ns;
> diff --git a/ipc/mq_sysctl.c b/ipc/mq_sysctl.c
> index e22336a..383d638 100644
> --- a/ipc/mq_sysctl.c
> +++ b/ipc/mq_sysctl.c
> @@ -73,6 +73,24 @@ static ctl_table mq_sysctls[] = {
>  		.extra1		= &msg_maxsize_limit_min,
>  		.extra2		= &msg_maxsize_limit_max,
>  	},
> +	{
> +		.procname	= "msg_default",
> +		.data		= &init_ipc_ns.mq_msg_default,
> +		.maxlen		= sizeof(int),
> +		.mode		= 0644,
> +		.proc_handler	= proc_mq_dointvec_minmax,
> +		.extra1		= &msg_max_limit_min,
> +		.extra2		= &msg_max_limit_max,
> +	},
> +	{
> +		.procname	= "msgsize_default",
> +		.data		= &init_ipc_ns.mq_msgsize_default,
> +		.maxlen		= sizeof(int),
> +		.mode		= 0644,
> +		.proc_handler	= proc_mq_dointvec_minmax,
> +		.extra1		= &msg_maxsize_limit_min,
> +		.extra2		= &msg_maxsize_limit_max,
> +	},
>  	{}
>  };
>  
> diff --git a/ipc/mqueue.c b/ipc/mqueue.c
> index f9f0782..04cc77e 100644
> --- a/ipc/mqueue.c
> +++ b/ipc/mqueue.c
> @@ -142,9 +142,10 @@ static struct inode *mqueue_get_inode(struct super_block *sb,
>  		info->qsize = 0;
>  		info->user = NULL;	/* set when all is ok */
>  		memset(&info->attr, 0, sizeof(info->attr));
> -		info->attr.mq_maxmsg = min(ipc_ns->mq_msg_max, DFLT_MSG);
> -		info->attr.mq_msgsize =
> -			min(ipc_ns->mq_msgsize_max, DFLT_MSGSIZE);
> +		info->attr.mq_maxmsg = min(ipc_ns->mq_msg_max,
> +					   ipc_ns->mq_msg_default);
> +		info->attr.mq_msgsize = min(ipc_ns->mq_msgsize_max,
> +					    ipc_ns->mq_msgsize_default);
>  		if (attr) {
>  			info->attr.mq_maxmsg = attr->mq_maxmsg;
>  			info->attr.mq_msgsize = attr->mq_msgsize;
> @@ -1254,6 +1255,8 @@ int mq_init_ns(struct ipc_namespace *ns)
>  	ns->mq_queues_max    = DFLT_QUEUESMAX;
>  	ns->mq_msg_max       = DFLT_MSGMAX;
>  	ns->mq_msgsize_max   = DFLT_MSGSIZEMAX;
> +	ns->mq_msg_default   = DFLT_MSG;
> +	ns->mq_msgsize_default  = DFLT_MSGSIZE;
>  
>  	ns->mq_mnt = kern_mount_data(&mqueue_fs_type, ns);
>  	if (IS_ERR(ns->mq_mnt)) {
> -- 
> 1.7.7.6
> 
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