Re: [PATCH 1/2] ring-buffer: Introducing ring-buffer mapping functions
From: Vincent Donnefort <hidden>
Date: 2023-03-21 15:17:39
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On Mon, Mar 20, 2023 at 09:45:16PM -0400, Steven Rostedt wrote:
On Fri, 17 Mar 2023 14:33:09 +0000 Vincent Donnefort [off-list ref] wrote:quoted
Also, the meta-page being... a single page, this limits at the moment the number of pages in the ring-buffer that can be mapped: ~3MB on a 4K pages system.I hate this limitation, so I fixed it ;-)
Thanks a lot for having a look. Do you mind if I fold this in my patch for a V2?
quoted hunk ↗ jump to hunk
I added a meta_page_size field to the meta page, and user space can do: meta = mmap(NULL, page_size, PROT_READ, MAP_SHARED, fd, 0); if (meta == MAP_FAILED) pdie("mmap"); map = meta; meta_len = map->meta_page_size; if (meta_len > page_size) { munmap(meta, page_size); meta = mmap(NULL, meta_len, PROT_READ, MAP_SHARED, fd, 0); if (meta == MAP_FAILED) pdie("mmap"); map = meta; } This appears to work (but I'm still testing it). -- Stevediff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h index 24bcec754a35..12f3f7ee33d9 100644 --- a/include/uapi/linux/trace_mmap.h +++ b/include/uapi/linux/trace_mmap.h@@ -18,6 +18,7 @@ struct ring_buffer_meta_page { __u32 reader_page; __u32 nr_data_pages; /* doesn't take into account the reader_page */ __u32 data_page_head; /* index of data_pages[] */ + __u32 meta_page_size; /* size of the meta page */
Do we want a specific field here? That could be deduced from nr_data_pages() quite easily?
quoted hunk ↗ jump to hunk
__u32 data_pages[]; };diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 10a17e78cfe6..77c92e4a7adc 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c@@ -526,6 +526,7 @@ struct ring_buffer_per_cpu { u64 read_stamp; int mapped; + int meta_order; struct mutex mapping_lock; unsigned long *page_ids; /* ID to addr */ struct ring_buffer_meta_page *meta_page;@@ -5898,7 +5899,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer, EXPORT_SYMBOL_GPL(ring_buffer_read_page); #define META_PAGE_MAX_PAGES \ - ((PAGE_SIZE - (offsetof(struct ring_buffer_meta_page, data_page_head))) >> 2) + ((PAGE_SIZE - (offsetof(struct ring_buffer_meta_page, data_pages))) >> 2)
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