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Wed, 11 Jun 2025 23:12:14 -0700 (PDT) From: Jason Xing To: axboe@kernel.dk, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Jason Xing , Yushan Zhou Subject: [PATCH v5 2/5] relayfs: support a counter tracking if per-cpu buffers is full Date: Thu, 12 Jun 2025 14:11:58 +0800 Message-Id: <20250612061201.34272-3-kerneljasonxing@gmail.com> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20250612061201.34272-1-kerneljasonxing@gmail.com> References: <20250612061201.34272-1-kerneljasonxing@gmail.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Jason Xing When using relay mechanism, we often encounter the case where new data are lost or old unconsumed data are overwritten because of slow reader. Add 'full' field in per-cpu buffer structure to detect if the above case is happening. Relay has two modes: 1) non-overwrite mode, 2) overwrite mode. So buffer being full here respectively means: 1) relayfs doesn't intend to accept new data and then simply drop them, or 2) relayfs is going to start over again and overwrite old unread data with new data. Note: this counter doesn't need any explicit lock to protect from being modified by different threads for the better performance consideration. Writers calling __relay_write/relay_write should consider how to use the lock and ensure it performs under the lock protection, thus it's not necessary to add a new small lock here. Reviewed-by: Yushan Zhou Reviewed-by: Jens Axboe Reviewed-by: Masami Hiramatsu (Google) Signed-off-by: Jason Xing --- include/linux/relay.h | 9 +++++++++ kernel/relay.c | 8 +++++++- 2 files changed, 16 insertions(+), 1 deletion(-) diff --git a/include/linux/relay.h b/include/linux/relay.h index e10a0fdf4325..cd77eb285a48 100644 --- a/include/linux/relay.h +++ b/include/linux/relay.h @@ -28,6 +28,14 @@ */ #define RELAYFS_CHANNEL_VERSION 7 +/* + * Relay buffer statistics + */ +struct rchan_buf_stats +{ + unsigned int full_count; /* counter for buffer full */ +}; + /* * Per-cpu relay channel buffer */ @@ -43,6 +51,7 @@ struct rchan_buf struct irq_work wakeup_work; /* reader wakeup */ struct dentry *dentry; /* channel file dentry */ struct kref kref; /* channel buffer refcount */ + struct rchan_buf_stats stats; /* buffer stats */ struct page **page_array; /* array of current buffer pages */ unsigned int page_count; /* number of current buffer pages */ unsigned int finalized; /* buffer has been finalized */ diff --git a/kernel/relay.c b/kernel/relay.c index 94f79f52d826..eb3f630f3896 100644 --- a/kernel/relay.c +++ b/kernel/relay.c @@ -252,8 +252,13 @@ EXPORT_SYMBOL_GPL(relay_buf_full); static int relay_subbuf_start(struct rchan_buf *buf, void *subbuf, void *prev_subbuf) { + int full = relay_buf_full(buf); + + if (full) + buf->stats.full_count++; + if (!buf->chan->cb->subbuf_start) - return !relay_buf_full(buf); + return !full; return buf->chan->cb->subbuf_start(buf, subbuf, prev_subbuf); @@ -298,6 +303,7 @@ static void __relay_reset(struct rchan_buf *buf, unsigned int init) buf->finalized = 0; buf->data = buf->start; buf->offset = 0; + buf->stats.full_count = 0; for (i = 0; i < buf->chan->n_subbufs; i++) buf->padding[i] = 0; -- 2.43.5