From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) (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 B16923DDAF3 for ; Fri, 11 Sep 2026 19:39:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.70 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789155612; cv=none; b=sTciboykVZNwPjyFxPb3ZKernPNdPGirhK9kR3B0E+sqrq1u4BJpVavaC8wOX3Dza2hwuafl560LyobnXLBq8Y0qcoewBB8CJ5T9i8XbXxCiZLaqkSxn7CoVnuLYfTSrNRf9MVvI97U3txO6WN2ov1i2JjQFdLiokVfO1zSaLo0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789155612; c=relaxed/simple; bh=hHw7yRoGhvN7MS5FpP2lX23LuKJXsj+eKlavKiGW0rA=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=jBV+SYmFhpr+66RierraipWDDgdPamgFJeqvI2FMfGyH4CFoloz6bCT5axPQT+fuJo5ZarzqqG0GyHz3Ps6Fzp0Nv4fUIBTZJO5mQAoqEykvUGHs9D/cf/hRy/ThAlhMCemNAkQJfp9fOJpRKCAUmgfm/17P8hUKu0cMfYZ4ohA= 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=P/S3ST0L; arc=none smtp.client-ip=209.85.221.70 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="P/S3ST0L" Received: by mail-wr1-f70.google.com with SMTP id ffacd0b85a97d-486f18da958so549505f8f.0 for ; Fri, 11 Sep 2026 12:39:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1789155595; x=1789760395; 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=y+HXnPMMIZpskweD6Y6dmHOP8zh8fc/lEgtzHbrvfOQ=; b=P/S3ST0LySyP8FyzSRxlCptHKzPuatNMp4Xx4QWQGxFlAAXFpnAX6gAUiyMzy61ZP0 q7FG0R6MuXyQoJth7irrwG2j69KkR/jE/93JmPOmXF7RaNCPcLzoaLaon7lI4etV7kZ4 t8UPhypeK7r2yDe6U4KW3/cC13KKxQV7xzasVmoioG1EG1fiFKHaZ6V2zAJoKmqChkf5 UOQW/b5ixwoRDuUNxv7/Wd94zoZD4Hc7rQEpG5Upp4MjrWPXHxe4PQ9vpCexcX4xdtFT RroCrXIKTVQ797+3xpSqnFgCpairnxE763/fbG+bqA34KWpndzlAbbhDjGS4GqxOJHB9 fXAA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1789155595; x=1789760395; 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=y+HXnPMMIZpskweD6Y6dmHOP8zh8fc/lEgtzHbrvfOQ=; b=OyPG69Qarl2xvArJHcV0adUwiB2+FmH/uZPt92Yqr2QrDjeh//pf7TvtuIVWCcDYR/ 8fBmkmGwOUyjZRigXcQGpKH1h2SRRXrjeAtsKWfm5i+4gyVLhAjLRx67yg0nZ0p9JpFg UADMGYUFlXdxDOBwNNkstHIq5yOxtvm2Zs+TD+IomV48ZEKhrsA2RGLlBBbHbkt1wnyn gZwD9B3ayA8BGn4bco2Si8NQxwkiKVTGpchdsseprupHVY37YV9nOk0t1SNhbIgUx0ir jJFGnXotIHjcxnkaJdgwM+hJSRzQRpOoxivXi2mUBuFzO/7sEDB/KfPOlzsPS35s9hw1 YTBA== X-Forwarded-Encrypted: i=1; AKwUvBzqw5/jXFPybXHimQgrqQ+X9nxV4doVDimE+FzgswG1qeVB7FsuNDTJSjB5+8ZRxsrK1+0tXLxRx+Zx+sI=@vger.kernel.org X-Gm-Message-State: AFuF++llvEpezjnAoUnn8sGgi5iAl0jpIfkp1YNhzu0JlSqsXzFCzhUS aqIqdKipqrn7Q6BvTBIThb7ieTumAmWov/02YiKB2Osl9aB7d6owV4WwtNUfui1xMx2knV2V9Dj cZH2yLRi+svpRvBZDF0cXLQ== X-Received: from wrtl11.prod.google.com ([2002:a5d:4bcb:0:b0:47f:472f:4e85]) (user=vdonnefort job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6000:1001:b0:485:8ea0:da8c with SMTP id ffacd0b85a97d-486e987d543mr5838331f8f.16.1789155595237; Fri, 11 Sep 2026 12:39:55 -0700 (PDT) Date: Fri, 11 Sep 2026 20:39:37 +0100 In-Reply-To: <20260911193937.602202-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260911193937.602202-1-vdonnefort@google.com> X-Mailer: git-send-email 2.55.0.1007.g17ff1f9808-goog Message-ID: <20260911193937.602202-4-vdonnefort@google.com> Subject: [PATCH v2 3/3] 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_calculate_nr_pages() to formalize the requirement of two pages in a ring buffer. Signed-off-by: Vincent Donnefort --- include/linux/ring_buffer.h | 9 ++++++++- kernel/trace/ring_buffer.c | 32 +++++++++++++------------------ kernel/trace/simple_ring_buffer.c | 4 ++-- 3 files changed, 23 insertions(+), 22 deletions(-) diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index eac3e9080c3c..e4370064273e 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -98,6 +98,13 @@ 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 @@ -287,7 +294,7 @@ static inline struct ring_buffer_desc *__first_ring_buffer_desc(struct trace_buf static inline unsigned long __calc_nr_pages_ring_buffer_desc(size_t size) { /* Takes into account the reader page */ - return max(DIV_ROUND_UP(size, PAGE_SIZE - BUF_PAGE_HDR_SIZE), 2UL) + 1; + 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) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 9c03a555a6ba..7137781ab0b8 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_calculate_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_calculate_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_calculate_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_calculate_nr_pages(buffer, + old_capacity * buffer->buffers[cpu]->nr_pages); cpu_buffer->nr_pages_to_update = nr_pages; @@ -8095,7 +8089,7 @@ int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node) } /* allocate minimum pages, user can later expand it */ if (!nr_pages_same) - nr_pages = 2; + nr_pages = RING_BUFFER_MIN_NR_PAGES; buffer->buffers[cpu] = rb_allocate_cpu_buffer(buffer, nr_pages, cpu); if (!buffer->buffers[cpu]) { 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)); -- 2.55.0.1007.g17ff1f9808-goog