From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 40C1246C4BE for ; Mon, 7 Sep 2026 19:26:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.71 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788809212; cv=none; b=Wxo19IuDkyhSSbiAt9PK42/8P6DltAYv9izmOxT5MI8EMLRlv28bx3tzPU5Q8ZzB4JBeq3UII1yazvOKLhxa79ejQDLxpHhe4F0cfAwK/zwo94GnmdItvx0W9Z66DVlAJoa3XgQqsLt+R1TyRvvTIEVLj6Rm9Ys2ExVCUNdWuyI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788809212; c=relaxed/simple; bh=NynFTKt6RVr+op3xbyiJQrAs6KI2YX8pjMHi+7qOb8Q=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=WqUZCyRnB7mWhIgtwKnl2S2ciBaXCu3qA2ueheAHF3mX+dC4OY3Hhb3Z+Vv3JmLp+Vvy52Y/1UZimaTecLyn8MhgQumpOtz1odaj5kLNkQI0uNEwOEZhUtmh97zSn1ssxZrvXYe69iJO/mh0nTDI9TkbegfQ5HYOZSJTypb9fok= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=nbf18RL0; arc=none smtp.client-ip=209.85.128.71 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="nbf18RL0" Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-495689bfcc8so26156015e9.1 for ; Mon, 07 Sep 2026 12:26:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1788809208; x=1789414008; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=cCveXykaK8vLD9VcikbfF1R8BHSS4OZomyQEA0R1gnk=; b=nbf18RL0D/fKT8sXeYPEWsiu2bCUygluJtq72PzkukNS9YzDpbBiHozAfEYFG/7OFV 1UrzH5oAA9u1mN421FPh/uwRhWex59KReMkcLvB/exJAQ687uiXj5vNSb2brs6e8l+n1 rAvkmJ7yDI0l5IT7eD16whO+6fOe1Uq/gFe/Jz/Vk6YueQdAyOQNOIhdo4m7BG7UESNS pJv2nADrX9grc7w/QbbsrEqM7N7W6q1jwUj+0TXZQ9rET05oERTSYaMTPX9KHyyyxMze g/I8CBZuAmWiiD9j4qGWr25fXn5q4/ivD7wz0lK52KYikxZe4JPIApNA5jGiC2omNyyf HHCQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1788809208; x=1789414008; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=cCveXykaK8vLD9VcikbfF1R8BHSS4OZomyQEA0R1gnk=; b=lPt4xrG+T5Pm1vjbfzAHiahBDsVEnXuIFGWeq40CN8wtP2s7MdF/t3dsOAHXjufDau oAjdHDvB+0KGJZzAJ3rs84B/B0+9t4AMtlPjOyO/dEm28Thd1xr0FchkniAHU//qOIe+ Cxp9H5H7p2h4o/hWIDIS4oYOBZDebm7tRVgaMfWfYQp0wY08ySiZ4G6pljYB9fdqWHkq l8x34FQazIOyAy1NRL6ydshTNtP3fgWCLDPiaEnYITp+tqzRUW1BYgN9yTnXdQUlXfLO bu81tnDLMyvBJ4PbZW5+OXll7VlLmaD7C4YI+6/04rlnsPAy0CYghoQB892r1lLhHSCo d/NQ== X-Forwarded-Encrypted: i=1; AKwUvBzJYRpjR/YOxc/DFSEG5padsasjpZxQ4nQzPXwRwklr7x241TP9hoV/1Onbz33VOqI/TAUzgN3ZzMkv36C6EVLzkq8=@vger.kernel.org X-Gm-Message-State: AFuF++kVp/0pv6/3zq3vnO/SeJAe95IWRDrLkCU3tOW2D5XLASzHjSjZ Y5rMUlU0sKRY/N/zlzBOvL51jM+l+NUkG27Ep7Hapr0yCSjrgVvbAzNGlnpCyeLYkMIMT8Sc++0 LodvoJzOblC5mcDCUMyfr9g== X-Received: from wmbf11.prod.google.com ([2002:a05:600c:594b:b0:49c:cea7:ac80]) (user=vdonnefort job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:3b99:b0:499:bf0e:95c8 with SMTP id 5b1f17b1804b1-49cf81fb72amr262383675e9.1.1788809207764; Mon, 07 Sep 2026 12:26:47 -0700 (PDT) Date: Mon, 7 Sep 2026 20:26:43 +0100 In-Reply-To: <20260907192643.42513-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260907192643.42513-1-vdonnefort@google.com> X-Mailer: git-send-email 2.55.0.979.g7e5102b832-goog Message-ID: <20260907192643.42513-3-vdonnefort@google.com> Subject: [PATCH v1 2/2] ring-buffer: Unify ring buffer minimum page calculations From: Vincent Donnefort To: rostedt@goodmis.org, mhiramat@kernel.org, linux-trace-kernel@vger.kernel.org Cc: mathieu.desnoyers@efficios.com, kernel-team@android.com, linux-kernel@vger.kernel.org, Vincent Donnefort Content-Type: text/plain; charset="UTF-8" The codebase scatters hardcoded minimum page limits across multiple places. Introduce RING_BUFFER_MIN_NR_PAGES and rb_size_to_nr_pages() to formalize the requirement of two pages in a ring buffer. Remote and persistent ring buffers must account for the reader page. Signed-off-by: Vincent Donnefort diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index 7a1a92f87650..a9401b8ebc72 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -99,6 +99,13 @@ struct trace_buffer *__ring_buffer_alloc_range(unsigned long size, unsigned flag void *ring_buffer_meta_scratch(struct trace_buffer *buffer, unsigned int *size); +/* + * A minimum of 2 pages ensures we can always swap a page out of the ring + * buffer. This does not account for the reader page or any other page + * containing meta data used by static ring buffers. + */ +#define RING_BUFFER_MIN_NR_PAGES 2UL + /* * Because the ring buffer is generic, if other users of the ring buffer get * traced by ftrace, it can produce lockdep warnings. We need to keep each @@ -281,10 +288,15 @@ static inline struct ring_buffer_desc *__first_ring_buffer_desc(struct trace_buf return (struct ring_buffer_desc *)(&desc->__data[0]); } +static inline unsigned long __ring_buffer_size_to_desc_pages(size_t size) +{ + /* Takes into account the reader page */ + return max(DIV_ROUND_UP(size, PAGE_SIZE - BUF_PAGE_HDR_SIZE), RING_BUFFER_MIN_NR_PAGES) + 1; +} + static inline size_t trace_buffer_desc_size(size_t buffer_size, unsigned int nr_cpus) { - unsigned long nr_pages = - max(DIV_ROUND_UP(buffer_size, PAGE_SIZE - BUF_PAGE_HDR_SIZE), 2UL) + 1; + unsigned long nr_pages = __ring_buffer_size_to_desc_pages(buffer_size); struct ring_buffer_desc *rbdesc; /* Capped by ring_buffer_desc::nr_page_va */ diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 9c03a555a6ba..88e39d98332a 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -642,6 +642,11 @@ static __always_inline unsigned int rb_subbuf_max_data_size(struct trace_buffer return rb_subbuf_capacity(buffer) - RB_EVNT_HDR_SIZE - sizeof(event->array[0]); } +static unsigned long rb_size_to_nr_pages(struct trace_buffer *buffer, unsigned long size) +{ + return max(DIV_ROUND_UP(size, rb_subbuf_capacity(buffer)), RING_BUFFER_MIN_NR_PAGES); +} + /** * rb_subbuf_start - Get the start address of a subbuffer * @buffer: A trace buffer @@ -2865,7 +2870,7 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags, goto fail_free_buffers; /* Need at least two pages plus the reader page */ - if (nr_pages < 3) + if (nr_pages < RING_BUFFER_MIN_NR_PAGES + 1) goto fail_free_buffers; again: @@ -2877,7 +2882,7 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags, ptr += subbuf_size * nr_pages; } if (ptr > end) { - if (nr_pages <= 3) + if (nr_pages <= RING_BUFFER_MIN_NR_PAGES + 1) goto fail_free_buffers; nr_pages--; goto again; @@ -2900,13 +2905,10 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags, if (nr_pages > rb_static_max_pages()) goto fail_free_buffers; - if (nr_pages < 2) + if (nr_pages < RING_BUFFER_MIN_NR_PAGES) goto fail_free_buffers; } else { - /* need at least two pages */ - nr_pages = DIV_ROUND_UP(size, rb_subbuf_capacity(buffer)); - if (nr_pages < 2) - nr_pages = 2; + nr_pages = rb_size_to_nr_pages(buffer, size); } cpumask_set_cpu(cpu, buffer->cpumask); @@ -3319,11 +3321,7 @@ int ring_buffer_resize(struct trace_buffer *buffer, unsigned long size, mutex_lock(&buffer->mutex); atomic_inc(&buffer->resizing); - nr_pages = DIV_ROUND_UP(size, rb_subbuf_capacity(buffer)); - - /* we need a minimum of two pages */ - if (nr_pages < 2) - nr_pages = 2; + nr_pages = rb_size_to_nr_pages(buffer, size); if (cpu_id == RING_BUFFER_ALL_CPUS) { /* @@ -7495,12 +7493,8 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) } /* Update the number of pages to match the new size */ - nr_pages = old_capacity * buffer->buffers[cpu]->nr_pages; - nr_pages = DIV_ROUND_UP(nr_pages, rb_subbuf_capacity(buffer)); - - /* we need a minimum of two pages */ - if (nr_pages < 2) - nr_pages = 2; + nr_pages = rb_size_to_nr_pages(buffer, + old_capacity * buffer->buffers[cpu]->nr_pages); cpu_buffer->nr_pages_to_update = nr_pages; diff --git a/kernel/trace/simple_ring_buffer.c b/kernel/trace/simple_ring_buffer.c index 49913bb0057a..abfaf9bee12e 100644 --- a/kernel/trace/simple_ring_buffer.c +++ b/kernel/trace/simple_ring_buffer.c @@ -383,8 +383,8 @@ int simple_ring_buffer_init_mm(struct simple_rb_per_cpu *cpu_buffer, void *page; int i; - /* At least 1 reader page and two pages in the ring-buffer */ - if (desc->nr_page_va < 3) + /* At least RING_BUFFER_MIN_NR_PAGES and 1 reader page */ + if (desc->nr_page_va < RING_BUFFER_MIN_NR_PAGES + 1) return -EINVAL; memset(cpu_buffer, 0, sizeof(*cpu_buffer)); diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c index 2e0fdbb730b7..0d90e02b1f4b 100644 --- a/kernel/trace/trace_remote.c +++ b/kernel/trace/trace_remote.c @@ -994,7 +994,7 @@ int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t desc_size, desc->struct_len = min_desc_size; rb_desc = __first_ring_buffer_desc(desc); - nr_pages = max(DIV_ROUND_UP(buffer_size, PAGE_SIZE - BUF_PAGE_HDR_SIZE), 2UL) + 1; + nr_pages = __ring_buffer_size_to_desc_pages(buffer_size); for_each_cpu(cpu, cpumask) { unsigned int id; -- 2.55.0.979.g7e5102b832-goog