aboutsummaryrefslogtreecommitdiff
path: root/ipc
diff options
context:
space:
mode:
authorMarcus Gelderie <redmnic@gmail.com>2015-08-06 15:46:10 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2015-08-07 04:39:39 +0300
commitde54b9ac253787c366bbfb28d901a31954eb3511 (patch)
treed1892200d83e3813dab248a9ab421497d1f6e15b /ipc
parent4469942bbbe5ebf845e04971d8c74e9b6178f9fa (diff)
downloadleg-kernel-de54b9ac253787c366bbfb28d901a31954eb3511.tar.gz
ipc: modify message queue accounting to not take kernel data structures into account
A while back, the message queue implementation in the kernel was improved to use btrees to speed up retrieval of messages, in commit d6629859b36d ("ipc/mqueue: improve performance of send/recv"). That patch introducing the improved kernel handling of message queues (using btrees) has, as a by-product, changed the meaning of the QSIZE field in the pseudo-file created for the queue. Before, this field reflected the size of the user-data in the queue. Since, it also takes kernel data structures into account. For example, if 13 bytes of user data are in the queue, on my machine the file reports a size of 61 bytes. There was some discussion on this topic before (for example https://lkml.org/lkml/2014/10/1/115). Commenting on a th lkml, Michael Kerrisk gave the following background (https://lkml.org/lkml/2015/6/16/74): The pseudofiles in the mqueue filesystem (usually mounted at /dev/mqueue) expose fields with metadata describing a message queue. One of these fields, QSIZE, as originally implemented, showed the total number of bytes of user data in all messages in the message queue, and this feature was documented from the beginning in the mq_overview(7) page. In 3.5, some other (useful) work happened to break the user-space API in a couple of places, including the value exposed via QSIZE, which now includes a measure of kernel overhead bytes for the queue, a figure that renders QSIZE useless for its original purpose, since there's no way to deduce the number of overhead bytes consumed by the implementation. (The other user-space breakage was subsequently fixed.) This patch removes the accounting of kernel data structures in the queue. Reporting the size of these data-structures in the QSIZE field was a breaking change (see Michael's comment above). Without the QSIZE field reporting the total size of user-data in the queue, there is no way to deduce this number. It should be noted that the resource limit RLIMIT_MSGQUEUE is counted against the worst-case size of the queue (in both the old and the new implementation). Therefore, the kernel overhead accounting in QSIZE is not necessary to help the user understand the limitations RLIMIT imposes on the processes. Signed-off-by: Marcus Gelderie <redmnic@gmail.com> Acked-by: Doug Ledford <dledford@redhat.com> Acked-by: Michael Kerrisk <mtk.manpages@gmail.com> Acked-by: Davidlohr Bueso <dbueso@suse.de> Cc: David Howells <dhowells@redhat.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: John Duffy <jb_duffy@btinternet.com> Cc: Arto Bendiken <arto@bendiken.net> Cc: Manfred Spraul <manfred@colorfullife.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'ipc')
-rw-r--r--ipc/mqueue.c5
1 files changed, 0 insertions, 5 deletions
diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index a24ba9fe5bb8..161a1807e6ef 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -142,7 +142,6 @@ static int msg_insert(struct msg_msg *msg, struct mqueue_inode_info *info)
if (!leaf)
return -ENOMEM;
INIT_LIST_HEAD(&leaf->msg_list);
- info->qsize += sizeof(*leaf);
}
leaf->priority = msg->m_type;
rb_link_node(&leaf->rb_node, parent, p);
@@ -187,7 +186,6 @@ try_again:
"lazy leaf delete!\n");
rb_erase(&leaf->rb_node, &info->msg_tree);
if (info->node_cache) {
- info->qsize -= sizeof(*leaf);
kfree(leaf);
} else {
info->node_cache = leaf;
@@ -200,7 +198,6 @@ try_again:
if (list_empty(&leaf->msg_list)) {
rb_erase(&leaf->rb_node, &info->msg_tree);
if (info->node_cache) {
- info->qsize -= sizeof(*leaf);
kfree(leaf);
} else {
info->node_cache = leaf;
@@ -1034,7 +1031,6 @@ SYSCALL_DEFINE5(mq_timedsend, mqd_t, mqdes, const char __user *, u_msg_ptr,
/* Save our speculative allocation into the cache */
INIT_LIST_HEAD(&new_leaf->msg_list);
info->node_cache = new_leaf;
- info->qsize += sizeof(*new_leaf);
new_leaf = NULL;
} else {
kfree(new_leaf);
@@ -1142,7 +1138,6 @@ SYSCALL_DEFINE5(mq_timedreceive, mqd_t, mqdes, char __user *, u_msg_ptr,
/* Save our speculative allocation into the cache */
INIT_LIST_HEAD(&new_leaf->msg_list);
info->node_cache = new_leaf;
- info->qsize += sizeof(*new_leaf);
} else {
kfree(new_leaf);
}