Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933356AbbHXJSq (ORCPT ); Mon, 24 Aug 2015 05:18:46 -0400 Received: from mx2.suse.de ([195.135.220.15]:58307 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932792AbbHXJKM (ORCPT ); Mon, 24 Aug 2015 05:10:12 -0400 X-Amavis-Alert: BAD HEADER SECTION, Duplicate header field: "References" From: Jiri Slaby To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Marcus Gelderie , David Howells , Alexander Viro , John Duffy , Arto Bendiken , Manfred Spraul , Andrew Morton , Linus Torvalds , Jiri Slaby Subject: [PATCH 3.12 54/82] ipc: modify message queue accounting to not take kernel data structures into account Date: Mon, 24 Aug 2015 11:09:14 +0200 Message-Id: <9d2c0b53d01f36e1b733dab44100bebfbe1ef1d7.1440407339.git.jslaby@suse.cz> X-Mailer: git-send-email 2.5.0 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4802 Lines: 118 From: Marcus Gelderie 3.12-stable review patch. If anyone has any objections, please let me know. =============== commit de54b9ac253787c366bbfb28d901a31954eb3511 upstream. 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 Acked-by: Doug Ledford Acked-by: Michael Kerrisk Acked-by: Davidlohr Bueso Cc: David Howells Cc: Alexander Viro Cc: John Duffy Cc: Arto Bendiken Cc: Manfred Spraul Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Jiri Slaby --- ipc/mqueue.c | 5 ----- 1 file changed, 5 deletions(-) diff --git a/ipc/mqueue.c b/ipc/mqueue.c index bb0248fc5187..82bb5e81ef57 100644 --- a/ipc/mqueue.c +++ b/ipc/mqueue.c @@ -143,7 +143,6 @@ 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); @@ -188,7 +187,6 @@ 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; @@ -201,7 +199,6 @@ 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; @@ -1026,7 +1023,6 @@ 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); @@ -1133,7 +1129,6 @@ 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); } -- 2.5.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/