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b=ivEC5vxqWrqfqt2Hm6Hn6iCeYNnzu7EovJKwwBeq+v6JmKEyBu07DwpmPD4RNFYKf 5IVcVvYCv+gDC3NlAZ6b6JJhWN6sIAIPrnWASwRu5O9CUGrD67PEcXoi4+wkw1Lpcj 8aVn2Scis3niA+iuLVqchYQlqtOaBv0PCWgjCLLPtzpU5J8jGyfv+Ehvt2mS/gxu9p 2sIPETtaHYjWpUb/R88DlxAWD0aaklYU8WnZnSPW33R4FCflNEQCzyzFH4L7ihkPJ8 oAFO9etY44YihR6fjnVF/SbJlRy5luMG4oD1RAzLE8X2lUDWAm/wl5MKj/ZHbD3nL/ CGXCDNI9sT8UQ== Date: Thu, 18 Apr 2024 09:55:55 +0300 From: Mike Rapoport To: Vincent Donnefort Cc: rostedt@goodmis.org, mhiramat@kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, mathieu.desnoyers@efficios.com, kernel-team@android.com, rdunlap@infradead.org, linux-mm@kvack.org Subject: Re: [PATCH v20 2/5] ring-buffer: Introducing ring-buffer mapping functions Message-ID: References: <20240406173649.3210836-1-vdonnefort@google.com> <20240406173649.3210836-3-vdonnefort@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240406173649.3210836-3-vdonnefort@google.com> X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 69155120022 X-Stat-Signature: 8kkon79uewzwia644t1c4rumaah5cey7 X-HE-Tag: 1713423431-333992 X-HE-Meta: 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 /UzrGl/x +0Yurx/gvsAsDvjvs/r/Xqwf3st1+1qWzWtANqheXAN9yo5zXZ8S2zqsHog7Ktg/yDMbMjClNQdl3z927W0DzB9Pi3+1gGTPvD8S5IEOu0f38T+1G1qnaJIXDa5Bn0eIVue/T3mJqZUXWjXrbzli9TaaXhM77S56QxnEDdVr7Ru/QiyVj3QntwT9KAi4ye/ITPMfZOxj0urg7at9mHCYIXYOT0Qa4hKp7y0LxrZgiWVmXlh7SPlX33j1Xy0vYmlwyChSzxXgFIHofKog= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Apr 06, 2024 at 06:36:46PM +0100, Vincent Donnefort wrote: > In preparation for allowing the user-space to map a ring-buffer, add > a set of mapping functions: > > ring_buffer_{map,unmap}() > > And controls on the ring-buffer: > > ring_buffer_map_get_reader() /* swap reader and head */ > > Mapping the ring-buffer also involves: > > A unique ID for each subbuf of the ring-buffer, currently they are > only identified through their in-kernel VA. > > A meta-page, where are stored ring-buffer statistics and a > description for the current reader > > The linear mapping exposes the meta-page, and each subbuf of the > ring-buffer, ordered following their unique ID, assigned during the > first mapping. > > Once mapped, no subbuf can get in or out of the ring-buffer: the buffer > size will remain unmodified and the splice enabling functions will in > reality simply memcpy the data instead of swapping subbufs. > > CC: > Signed-off-by: Vincent Donnefort > > diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h > index dc5ae4e96aee..96d2140b471e 100644 > --- a/include/linux/ring_buffer.h > +++ b/include/linux/ring_buffer.h > @@ -6,6 +6,8 @@ > #include > #include > > +#include > + > struct trace_buffer; > struct ring_buffer_iter; > > @@ -223,4 +225,8 @@ int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node); > #define trace_rb_cpu_prepare NULL > #endif > > +int ring_buffer_map(struct trace_buffer *buffer, int cpu, > + struct vm_area_struct *vma); > +int ring_buffer_unmap(struct trace_buffer *buffer, int cpu); > +int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu); > #endif /* _LINUX_RING_BUFFER_H */ > diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h > new file mode 100644 > index 000000000000..ffcd8dfcaa4f > --- /dev/null > +++ b/include/uapi/linux/trace_mmap.h > @@ -0,0 +1,46 @@ > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ > +#ifndef _TRACE_MMAP_H_ > +#define _TRACE_MMAP_H_ > + > +#include > + > +/** > + * struct trace_buffer_meta - Ring-buffer Meta-page description > + * @meta_page_size: Size of this meta-page. > + * @meta_struct_len: Size of this structure. > + * @subbuf_size: Size of each sub-buffer. > + * @nr_subbufs: Number of subbfs in the ring-buffer, including the reader. > + * @reader.lost_events: Number of events lost at the time of the reader swap. > + * @reader.id: subbuf ID of the current reader. ID range [0 : @nr_subbufs - 1] > + * @reader.read: Number of bytes read on the reader subbuf. > + * @flags: Placeholder for now, 0 until new features are supported. > + * @entries: Number of entries in the ring-buffer. > + * @overrun: Number of entries lost in the ring-buffer. > + * @read: Number of entries that have been read. > + * @Reserved1: Reserved for future use. > + * @Reserved2: Reserved for future use. > + */ > +struct trace_buffer_meta { > + __u32 meta_page_size; > + __u32 meta_struct_len; > + > + __u32 subbuf_size; > + __u32 nr_subbufs; > + > + struct { > + __u64 lost_events; > + __u32 id; > + __u32 read; > + } reader; > + > + __u64 flags; > + > + __u64 entries; > + __u64 overrun; > + __u64 read; > + > + __u64 Reserved1; > + __u64 Reserved2; Why do you need reserved fields? This structure always resides in the beginning of a page and the rest of the page is essentially "reserved". > +}; > + > +#endif /* _TRACE_MMAP_H_ */ > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index cc9ebe593571..793ecc454039 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c ... > +static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer, > + unsigned long *subbuf_ids) > +{ > + struct trace_buffer_meta *meta = cpu_buffer->meta_page; > + unsigned int nr_subbufs = cpu_buffer->nr_pages + 1; > + struct buffer_page *first_subbuf, *subbuf; > + int id = 0; > + > + subbuf_ids[id] = (unsigned long)cpu_buffer->reader_page->page; > + cpu_buffer->reader_page->id = id++; > + > + first_subbuf = subbuf = rb_set_head_page(cpu_buffer); > + do { > + if (WARN_ON(id >= nr_subbufs)) > + break; > + > + subbuf_ids[id] = (unsigned long)subbuf->page; > + subbuf->id = id; > + > + rb_inc_page(&subbuf); > + id++; > + } while (subbuf != first_subbuf); > + > + /* install subbuf ID to kern VA translation */ > + cpu_buffer->subbuf_ids = subbuf_ids; > + > + /* __rb_map_vma() pads the meta-page to align it with the sub-buffers */ > + meta->meta_page_size = PAGE_SIZE << cpu_buffer->buffer->subbuf_order; Isn't this a single page? > + meta->meta_struct_len = sizeof(*meta); > + meta->nr_subbufs = nr_subbufs; > + meta->subbuf_size = cpu_buffer->buffer->subbuf_size + BUF_PAGE_HDR_SIZE; > + > + rb_update_meta_page(cpu_buffer); > +} ... > +#define subbuf_page(off, start) \ > + virt_to_page((void *)((start) + ((off) << PAGE_SHIFT))) > + > +#define foreach_subbuf_page(sub_order, start, page) \ Nit: usually iterators in kernel use for_each > + page = subbuf_page(0, (start)); \ > + for (int __off = 0; __off < (1 << (sub_order)); \ > + __off++, page = subbuf_page(__off, (start))) The pages are allocated with alloc_pages_node(.. subbuf_order) are physically contiguous and struct pages for them are also contiguous, so inside a subbuf_order allocation you can just do page++. -- Sincerely yours, Mike.