Messages in this thread |  | | | Date | Thu, 03 May 2012 09:03:44 -0400 | | From | Doug Ledford <> | | Subject | Re: [Patch 1/4] ipc/mqueue: improve performance of send/recv |
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On 5/3/2012 5:21 AM, Dan Carpenter wrote: > On Tue, May 01, 2012 at 01:50:52PM -0400, Doug Ledford wrote: >> @@ -150,16 +241,25 @@ static struct inode *mqueue_get_inode(struct super_block *sb, >> info->attr.mq_maxmsg = attr->mq_maxmsg; >> info->attr.mq_msgsize = attr->mq_msgsize; >> } >> - mq_msg_tblsz = info->attr.mq_maxmsg * sizeof(struct msg_msg *); >> - if (mq_msg_tblsz > PAGE_SIZE) >> - info->messages = vmalloc(mq_msg_tblsz); >> - else >> - info->messages = kmalloc(mq_msg_tblsz, GFP_KERNEL); >> - if (!info->messages) >> - goto out_inode; >> + /* >> + * We used to allocate a static array of pointers and account >> + * the size of that array as well as one msg_msg struct per >> + * possible message into the queue size. That's no longer >> + * accurate as the queue is now an rbtree and will grow and >> + * shrink depending on usage patterns. We can, however, still >> + * account one msg_msg struct per message, but the nodes are >> + * allocated depending on priority usage, and most programs >> + * only use one, or a handful, of priorities. However, since >> + * this is pinned memory, we need to assume worst case, so >> + * that means the min(mq_maxmsg, max_priorities) * struct >> + * posix_msg_tree_node. >> + */ >> + mq_treesize = info->attr.mq_maxmsg * sizeof(struct msg_msg) + >> + min_t(unsigned int, info->attr.mq_maxmsg, MQ_PRIO_MAX) * >> + sizeof(struct posix_msg_tree_node); > > "info->attr.mq_maxmsg" is a long, but the min_t() truncates it to an > unsigned int. I'm not familiar with this code so I don't know if > that's a problem...
It's fine. We currently cap mq_maxmsg at a hard limit of 65536, and MQ_PRIO_MAX is 32768, so both well within the limits of truncating a long to unsigned int. In order for this to ever be a problem, we would first have to change the accounting of mq bytes in the user struct from a 32bit type to a 64bit type. As long as it's still 32 bits, and as long as mq_maxmsg * (sizeof(struct msg_msg) + mq_msgsize) must fit within that 32bit struct, we will never have an mq_maxmsg large enough to truncate in this situation.
> We do the same thing in mqueue_evict_inode() and mq_attr_ok().
All of the math in here would need an audit if we increased the maximum mq bytes from 32bit to 64bit.
-- Doug Ledford <dledford@redhat.com> GPG KeyID: 0E572FDD http://people.redhat.com/dledford
Infiniband specific RPMs available at http://people.redhat.com/dledford/Infiniband
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