lkml.org 
[lkml]   [2012]   [May]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [Patch 1/4] ipc/mqueue: improve performance of send/recv
    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

    [unhandled content-type:application/pgp-signature]
    \
     
     \ /
      Last update: 2012-05-03 15:41    [W:0.028 / U:0.572 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site