From patchwork Fri Feb 9 11:36:22 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steven Rostedt X-Patchwork-Id: 13551124 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 70C931D542; Fri, 9 Feb 2024 11:36:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707478587; cv=none; b=qTIYa4grV7Q2xolLnqeJLIhMHIY3XI9YfyLHxEH2ObhcR7ik+X/ovRun9lZCrFj9AmBrbX1l6NaiV5M16oT1ZqlejqdnouYQiVUVMLr09o638YxewzOY/PTG0gCSTjmGtEofP5R1KJOBzxC6U8r1atfJSVTit5oeiU01/pERdrg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707478587; c=relaxed/simple; bh=lQCt5IpvlhoGD78imhrQYoo7a8ZPzBS9q7DvLNIcdeM=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type; b=mraesiliZuQSuU5KLbHWMIITwBAcsHXHhxW/V8Pv71NPY5SpUoUpchALudBCB/55lBgf4s4XUZPjmPdvGwenXIslQI2F5xKpNPrTlf1YcTEYiFiHQRrxCbgUxHj5lyN+rEQZjLm2WPw666yv5Ef3NC6j1u6N5HP5yK7FQylyYrk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id BA21AC433F1; Fri, 9 Feb 2024 11:36:25 +0000 (UTC) Date: Fri, 9 Feb 2024 06:36:22 -0500 From: Steven Rostedt To: LKML , Linux trace kernel Cc: Masami Hiramatsu , Mathieu Desnoyers , Vincent Donnefort , Sven Schnelle , Mete Durlu Subject: [PATCH v2] tracing: Fix wasted memory in saved_cmdlines logic Message-ID: <20240209063622.1f7b6d5f@rorschach.local.home> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: "Steven Rostedt (Google)" While looking at improving the saved_cmdlines cache I found a huge amount of wasted memory that should be used for the cmdlines. The tracing data saves pids during the trace. At sched switch, if a trace occurred, it will save the comm of the task that did the trace. This is saved in a "cache" that maps pids to comms and exposed to user space via the /sys/kernel/tracing/saved_cmdlines file. Currently it only caches by default 128 comms. The structure that uses this creates an array to store the pids using PID_MAX_DEFAULT (which is usually set to 32768). This causes the structure to be of the size of 131104 bytes on 64 bit machines. In hex: 131104 = 0x20020, and since the kernel allocates generic memory in powers of two, the kernel would allocate 0x40000 or 262144 bytes to store this structure. That leaves 131040 bytes of wasted space. Worse, the structure points to an allocated array to store the comm names, which is 16 bytes times the amount of names to save (currently 128), which is 2048 bytes. Instead of allocating a separate array, make the structure end with a variable length string and use the extra space for that. This is similar to a recommendation that Linus had made about eventfs_inode names: https://lore.kernel.org/all/20240130190355.11486-5-torvalds@linux-foundation.org/ Instead of allocating a separate string array to hold the saved comms, have the structure end with: char saved_cmdlines[]; and round up to the next power of two over sizeof(struct saved_cmdline_buffers) + num_cmdlines * TASK_COMM_LEN It will use this extra space for the saved_cmdline portion. Now, instead of saving only 128 comms by default, by using this wasted space at the end of the structure it can save over 8000 comms and even saves space by removing the need for allocating the other array. Cc: stable@vger.kernel.org Fixes: 939c7a4f04fcd ("tracing: Introduce saved_cmdlines_size file") Signed-off-by: Steven Rostedt (Google) Acked-by: Masami Hiramatsu (Google) --- Changes since v1: https://lore.kernel.org/linux-trace-kernel/20240208105328.7e73f71d@rorschach.local.home - Added back error check of s->map_cmdline_to_pid allocation failure kernel/trace/trace.c | 75 ++++++++++++++++++++++---------------------- 1 file changed, 37 insertions(+), 38 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 2a7c6fd934e9..9ff8a439d674 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2320,7 +2320,7 @@ struct saved_cmdlines_buffer { unsigned *map_cmdline_to_pid; unsigned cmdline_num; int cmdline_idx; - char *saved_cmdlines; + char saved_cmdlines[]; }; static struct saved_cmdlines_buffer *savedcmd; @@ -2334,47 +2334,58 @@ static inline void set_cmdline(int idx, const char *cmdline) strncpy(get_saved_cmdlines(idx), cmdline, TASK_COMM_LEN); } -static int allocate_cmdlines_buffer(unsigned int val, - struct saved_cmdlines_buffer *s) +static void free_saved_cmdlines_buffer(struct saved_cmdlines_buffer *s) +{ + int order = get_order(sizeof(*s) + s->cmdline_num * TASK_COMM_LEN); + + kfree(s->map_cmdline_to_pid); + free_pages((unsigned long)s, order); +} + +static struct saved_cmdlines_buffer *allocate_cmdlines_buffer(unsigned int val) { + struct saved_cmdlines_buffer *s; + struct page *page; + int orig_size, size; + int order; + + /* Figure out how much is needed to hold the given number of cmdlines */ + orig_size = sizeof(*s) + val * TASK_COMM_LEN; + order = get_order(orig_size); + size = 1 << (order + PAGE_SHIFT); + page = alloc_pages(GFP_KERNEL, order); + if (!page) + return NULL; + + s = page_address(page); + memset(s, 0, sizeof(*s)); + + /* Round up to actual allocation */ + val = (size - sizeof(*s)) / TASK_COMM_LEN; + s->cmdline_num = val; + s->map_cmdline_to_pid = kmalloc_array(val, sizeof(*s->map_cmdline_to_pid), GFP_KERNEL); - if (!s->map_cmdline_to_pid) - return -ENOMEM; - - s->saved_cmdlines = kmalloc_array(TASK_COMM_LEN, val, GFP_KERNEL); - if (!s->saved_cmdlines) { - kfree(s->map_cmdline_to_pid); - return -ENOMEM; + if (!s->map_cmdline_to_pid) { + free_saved_cmdlines_buffer(s); + return NULL; } s->cmdline_idx = 0; - s->cmdline_num = val; memset(&s->map_pid_to_cmdline, NO_CMDLINE_MAP, sizeof(s->map_pid_to_cmdline)); memset(s->map_cmdline_to_pid, NO_CMDLINE_MAP, val * sizeof(*s->map_cmdline_to_pid)); - return 0; + return s; } static int trace_create_savedcmd(void) { - int ret; - - savedcmd = kmalloc(sizeof(*savedcmd), GFP_KERNEL); - if (!savedcmd) - return -ENOMEM; - - ret = allocate_cmdlines_buffer(SAVED_CMDLINES_DEFAULT, savedcmd); - if (ret < 0) { - kfree(savedcmd); - savedcmd = NULL; - return -ENOMEM; - } + savedcmd = allocate_cmdlines_buffer(SAVED_CMDLINES_DEFAULT); - return 0; + return savedcmd ? 0 : -ENOMEM; } int is_tracing_stopped(void) @@ -6056,26 +6067,14 @@ tracing_saved_cmdlines_size_read(struct file *filp, char __user *ubuf, return simple_read_from_buffer(ubuf, cnt, ppos, buf, r); } -static void free_saved_cmdlines_buffer(struct saved_cmdlines_buffer *s) -{ - kfree(s->saved_cmdlines); - kfree(s->map_cmdline_to_pid); - kfree(s); -} - static int tracing_resize_saved_cmdlines(unsigned int val) { struct saved_cmdlines_buffer *s, *savedcmd_temp; - s = kmalloc(sizeof(*s), GFP_KERNEL); + s = allocate_cmdlines_buffer(val); if (!s) return -ENOMEM; - if (allocate_cmdlines_buffer(val, s) < 0) { - kfree(s); - return -ENOMEM; - } - preempt_disable(); arch_spin_lock(&trace_cmdline_lock); savedcmd_temp = savedcmd;