Re: [PATCH v20 0/5] Introducing trace buffer mapping by user-space
(added linux-mm)
On Wed, Apr 10, 2024 at 01:56:12PM -0400, Steven Rostedt wrote:
>
> Hi Andrew, et.al.
>
> Linus said it's a hard requirement that this code gets an Acked-by (or
> Reviewed-by) from the memory sub-maintainers before he will accept it.
> He was upset that we faulted in pages one at a time instead of mapping it
> in one go:
>
>
> https://lore.kernel.org/all/CAHk-=wh5wWeib7+kVHpBVtUn7kx7GGadWqb5mW5FYTdewEfL=w...@mail.gmail.com/
>
> Could you take a look at patches 1-3 to make sure they look sane from a
> memory management point of view?
>
> I really want this applied in the next merge window.
>
> Thanks!
>
> -- Steve
>
>
> On Sat, 6 Apr 2024 18:36:44 +0100
> Vincent Donnefort wrote:
>
> > The tracing ring-buffers can be stored on disk or sent to network
> > without any copy via splice. However the later doesn't allow real time
> > processing of the traces. A solution is to give userspace direct access
> > to the ring-buffer pages via a mapping. An application can now become a
> > consumer of the ring-buffer, in a similar fashion to what trace_pipe
> > offers.
> >
> > Support for this new feature can already be found in libtracefs from
> > version 1.8, when built with EXTRA_CFLAGS=-DFORCE_MMAP_ENABLE.
> >
> > Vincent
> >
> > v19 -> v20:
> > * Fix typos in documentation.
> > * Remove useless mmap open and fault callbacks.
> > * add mm.h include for vm_insert_pages
> >
> > v18 -> v19:
> > * Use VM_PFNMAP and vm_insert_pages
> > * Allocate ring-buffer subbufs with __GFP_COMP
> > * Pad the meta-page with the zero-page to align on the subbuf_order
> > * Extend the ring-buffer test with mmap() dedicated suite
> >
> > v17 -> v18:
> > * Fix lockdep_assert_held
> > * Fix spin_lock_init typo
> > * Fix CONFIG_TRACER_MAX_TRACE typo
> >
> > v16 -> v17:
> > * Documentation and comments improvements.
> > * Create get/put_snapshot_map() for clearer code.
> > * Replace kzalloc with kcalloc.
> > * Fix -ENOMEM handling in rb_alloc_meta_page().
> > * Move flush(cpu_buffer->reader_page) behind the reader lock.
> > * Move all inc/dec of cpu_buffer->mapped behind reader lock and buffer
> > mutex. (removes READ_ONCE/WRITE_ONCE accesses).
> >
> > v15 -> v16:
> > * Add comment for the dcache flush.
> > * Remove now unnecessary WRITE_ONCE for the meta-page.
> >
> > v14 -> v15:
> > * Add meta-page and reader-page flush. Intends to fix the mapping
> > for VIVT and aliasing-VIPT data caches.
> > * -EPERM on VM_EXEC.
> > * Fix build warning !CONFIG_TRACER_MAX_TRACE.
> >
> > v13 -> v14:
> > * All cpu_buffer->mapped readers use READ_ONCE (except for swap_cpu)
> > * on unmap, sync meta-page teardown with the reader_lock instead of
> > the synchronize_rcu.
> > * Add a dedicated spinlock for trace_array ->snapshot and ->mapped.
> > (intends to fix a lockdep issue)
> > * Add kerneldoc for flags and Reserved fields.
> > * Add kselftest for snapshot/map mutual exclusion.
> >
> > v12 -> v13:
> > * Swap subbufs_{touched,lost} for Reserved fields.
> > * Add a flag field in the meta-page.
> > * Fix CONFIG_TRACER_MAX_TRACE.
> > * Rebase on top of trace/urgent.
> > * Add a comment for try_unregister_trigger()
> >
> > v11 -> v12:
> > * Fix code sample mmap bug.
> > * Add logging in sample code.
> > * Reset tracer in selftest.
> > * Add a refcount for the snapshot users.
> > * Prevent mapping when there are snapshot users and vice versa.
> > * Refine the meta-page.
> > * Fix types in the meta-page.
> > * Collect Reviewed-by.
> >
> > v10 -> v11:
> > * Add Documentation and code sample.
> > * Add a selftest.
> > * Move all the update to the meta-page into a single
> > rb_update_meta_page().
> > * rb_update_meta_page() is now called from
> > ring_buffer_map_get_reader() to fix NOBLOCK callers.
> > * kerneldoc for struct trace_meta_page.
> > * Add a patch to zero all the ring-buffer allocations.
> >
> > v9 -> v10:
> > * Refactor rb_update_meta_page()
> > * In-loop declaration for foreach_subbuf_page()
> > * Check for cpu_buffer->mapped overflow
> >
> > v8 -> v9:
> > * Fix the unlock path in ring_buffer_map()
> > * Fix cpu_buffer cast with rb_work_rq->is_cpu_buffer
> > * Rebase on linux-trace/for-next
> > (3cb3091138ca0921c4569bcf7ffa062519639b6a)
> >
> > v7 -> v8:
> > * Drop the subbufs renaming into bpages
> > * Use subbuf as a name when relevant
> >
> > v6 -> v7:
> > * Rebase onto lore.kernel.org/lkml/20231215175502.106587...@goodmis.org/
> > * Support for subbufs
> > * Rename subbufs into bpages
> >
> > v5 -> v6:
> > * Rebase on next-20230802.
> > * (unsigned long) -> (void *) cast for virt_to_page().
> > * Add a wait for the GET_READER_PAGE ioctl.
> > * Move writer fields update (overrun/pages_lost/entries/pages_touched)
> > in the irq_work.
> > * Rearrange id in struct buffer_page.
> > * Rearrange the meta-page.
> > * ring_buffer_meta_page ->
Re: [PATCH v20 0/5] Introducing trace buffer mapping by user-space
Hi Andrew, et.al.
Linus said it's a hard requirement that this code gets an Acked-by (or
Reviewed-by) from the memory sub-maintainers before he will accept it.
He was upset that we faulted in pages one at a time instead of mapping it
in one go:
https://lore.kernel.org/all/CAHk-=wh5wWeib7+kVHpBVtUn7kx7GGadWqb5mW5FYTdewEfL=w...@mail.gmail.com/
Could you take a look at patches 1-3 to make sure they look sane from a
memory management point of view?
I really want this applied in the next merge window.
Thanks!
-- Steve
On Sat, 6 Apr 2024 18:36:44 +0100
Vincent Donnefort wrote:
> The tracing ring-buffers can be stored on disk or sent to network
> without any copy via splice. However the later doesn't allow real time
> processing of the traces. A solution is to give userspace direct access
> to the ring-buffer pages via a mapping. An application can now become a
> consumer of the ring-buffer, in a similar fashion to what trace_pipe
> offers.
>
> Support for this new feature can already be found in libtracefs from
> version 1.8, when built with EXTRA_CFLAGS=-DFORCE_MMAP_ENABLE.
>
> Vincent
>
> v19 -> v20:
> * Fix typos in documentation.
> * Remove useless mmap open and fault callbacks.
> * add mm.h include for vm_insert_pages
>
> v18 -> v19:
> * Use VM_PFNMAP and vm_insert_pages
> * Allocate ring-buffer subbufs with __GFP_COMP
> * Pad the meta-page with the zero-page to align on the subbuf_order
> * Extend the ring-buffer test with mmap() dedicated suite
>
> v17 -> v18:
> * Fix lockdep_assert_held
> * Fix spin_lock_init typo
> * Fix CONFIG_TRACER_MAX_TRACE typo
>
> v16 -> v17:
> * Documentation and comments improvements.
> * Create get/put_snapshot_map() for clearer code.
> * Replace kzalloc with kcalloc.
> * Fix -ENOMEM handling in rb_alloc_meta_page().
> * Move flush(cpu_buffer->reader_page) behind the reader lock.
> * Move all inc/dec of cpu_buffer->mapped behind reader lock and buffer
> mutex. (removes READ_ONCE/WRITE_ONCE accesses).
>
> v15 -> v16:
> * Add comment for the dcache flush.
> * Remove now unnecessary WRITE_ONCE for the meta-page.
>
> v14 -> v15:
> * Add meta-page and reader-page flush. Intends to fix the mapping
> for VIVT and aliasing-VIPT data caches.
> * -EPERM on VM_EXEC.
> * Fix build warning !CONFIG_TRACER_MAX_TRACE.
>
> v13 -> v14:
> * All cpu_buffer->mapped readers use READ_ONCE (except for swap_cpu)
> * on unmap, sync meta-page teardown with the reader_lock instead of
> the synchronize_rcu.
> * Add a dedicated spinlock for trace_array ->snapshot and ->mapped.
> (intends to fix a lockdep issue)
> * Add kerneldoc for flags and Reserved fields.
> * Add kselftest for snapshot/map mutual exclusion.
>
> v12 -> v13:
> * Swap subbufs_{touched,lost} for Reserved fields.
> * Add a flag field in the meta-page.
> * Fix CONFIG_TRACER_MAX_TRACE.
> * Rebase on top of trace/urgent.
> * Add a comment for try_unregister_trigger()
>
> v11 -> v12:
> * Fix code sample mmap bug.
> * Add logging in sample code.
> * Reset tracer in selftest.
> * Add a refcount for the snapshot users.
> * Prevent mapping when there are snapshot users and vice versa.
> * Refine the meta-page.
> * Fix types in the meta-page.
> * Collect Reviewed-by.
>
> v10 -> v11:
> * Add Documentation and code sample.
> * Add a selftest.
> * Move all the update to the meta-page into a single
> rb_update_meta_page().
> * rb_update_meta_page() is now called from
> ring_buffer_map_get_reader() to fix NOBLOCK callers.
> * kerneldoc for struct trace_meta_page.
> * Add a patch to zero all the ring-buffer allocations.
>
> v9 -> v10:
> * Refactor rb_update_meta_page()
> * In-loop declaration for foreach_subbuf_page()
> * Check for cpu_buffer->mapped overflow
>
> v8 -> v9:
> * Fix the unlock path in ring_buffer_map()
> * Fix cpu_buffer cast with rb_work_rq->is_cpu_buffer
> * Rebase on linux-trace/for-next (3cb3091138ca0921c4569bcf7ffa062519639b6a)
>
> v7 -> v8:
> * Drop the subbufs renaming into bpages
> * Use subbuf as a name when relevant
>
> v6 -> v7:
> * Rebase onto lore.kernel.org/lkml/20231215175502.106587...@goodmis.org/
> * Support for subbufs
> * Rename subbufs into bpages
>
> v5 -> v6:
> * Rebase on next-20230802.
> * (unsigned long) -> (void *) cast for virt_to_page().
> * Add a wait for the GET_READER_PAGE ioctl.
> * Move writer fields update (overrun/pages_lost/entries/pages_touched)
> in the irq_work.
> * Rearrange id in struct buffer_page.
> * Rearrange the meta-page.
> * ring_buffer_meta_page -> trace_buffer_meta_page.
> * Add meta_struct_len into the meta-page.
>
> v4 -> v5:
> * Trivial rebase onto 6.5-rc3 (previously 6.4-rc3)
>
> v3 -> v4:
> * Add to the meta-page:
>- pages_lost / pages_read (allow to compute how full is the
>ring-buffer)
>- read (allow to compute how many entries can be read)
>- A reader_page
[PATCH v20 0/5] Introducing trace buffer mapping by user-space
The tracing ring-buffers can be stored on disk or sent to network
without any copy via splice. However the later doesn't allow real time
processing of the traces. A solution is to give userspace direct access
to the ring-buffer pages via a mapping. An application can now become a
consumer of the ring-buffer, in a similar fashion to what trace_pipe
offers.
Support for this new feature can already be found in libtracefs from
version 1.8, when built with EXTRA_CFLAGS=-DFORCE_MMAP_ENABLE.
Vincent
v19 -> v20:
* Fix typos in documentation.
* Remove useless mmap open and fault callbacks.
* add mm.h include for vm_insert_pages
v18 -> v19:
* Use VM_PFNMAP and vm_insert_pages
* Allocate ring-buffer subbufs with __GFP_COMP
* Pad the meta-page with the zero-page to align on the subbuf_order
* Extend the ring-buffer test with mmap() dedicated suite
v17 -> v18:
* Fix lockdep_assert_held
* Fix spin_lock_init typo
* Fix CONFIG_TRACER_MAX_TRACE typo
v16 -> v17:
* Documentation and comments improvements.
* Create get/put_snapshot_map() for clearer code.
* Replace kzalloc with kcalloc.
* Fix -ENOMEM handling in rb_alloc_meta_page().
* Move flush(cpu_buffer->reader_page) behind the reader lock.
* Move all inc/dec of cpu_buffer->mapped behind reader lock and buffer
mutex. (removes READ_ONCE/WRITE_ONCE accesses).
v15 -> v16:
* Add comment for the dcache flush.
* Remove now unnecessary WRITE_ONCE for the meta-page.
v14 -> v15:
* Add meta-page and reader-page flush. Intends to fix the mapping
for VIVT and aliasing-VIPT data caches.
* -EPERM on VM_EXEC.
* Fix build warning !CONFIG_TRACER_MAX_TRACE.
v13 -> v14:
* All cpu_buffer->mapped readers use READ_ONCE (except for swap_cpu)
* on unmap, sync meta-page teardown with the reader_lock instead of
the synchronize_rcu.
* Add a dedicated spinlock for trace_array ->snapshot and ->mapped.
(intends to fix a lockdep issue)
* Add kerneldoc for flags and Reserved fields.
* Add kselftest for snapshot/map mutual exclusion.
v12 -> v13:
* Swap subbufs_{touched,lost} for Reserved fields.
* Add a flag field in the meta-page.
* Fix CONFIG_TRACER_MAX_TRACE.
* Rebase on top of trace/urgent.
* Add a comment for try_unregister_trigger()
v11 -> v12:
* Fix code sample mmap bug.
* Add logging in sample code.
* Reset tracer in selftest.
* Add a refcount for the snapshot users.
* Prevent mapping when there are snapshot users and vice versa.
* Refine the meta-page.
* Fix types in the meta-page.
* Collect Reviewed-by.
v10 -> v11:
* Add Documentation and code sample.
* Add a selftest.
* Move all the update to the meta-page into a single
rb_update_meta_page().
* rb_update_meta_page() is now called from
ring_buffer_map_get_reader() to fix NOBLOCK callers.
* kerneldoc for struct trace_meta_page.
* Add a patch to zero all the ring-buffer allocations.
v9 -> v10:
* Refactor rb_update_meta_page()
* In-loop declaration for foreach_subbuf_page()
* Check for cpu_buffer->mapped overflow
v8 -> v9:
* Fix the unlock path in ring_buffer_map()
* Fix cpu_buffer cast with rb_work_rq->is_cpu_buffer
* Rebase on linux-trace/for-next (3cb3091138ca0921c4569bcf7ffa062519639b6a)
v7 -> v8:
* Drop the subbufs renaming into bpages
* Use subbuf as a name when relevant
v6 -> v7:
* Rebase onto lore.kernel.org/lkml/20231215175502.106587...@goodmis.org/
* Support for subbufs
* Rename subbufs into bpages
v5 -> v6:
* Rebase on next-20230802.
* (unsigned long) -> (void *) cast for virt_to_page().
* Add a wait for the GET_READER_PAGE ioctl.
* Move writer fields update (overrun/pages_lost/entries/pages_touched)
in the irq_work.
* Rearrange id in struct buffer_page.
* Rearrange the meta-page.
* ring_buffer_meta_page -> trace_buffer_meta_page.
* Add meta_struct_len into the meta-page.
v4 -> v5:
* Trivial rebase onto 6.5-rc3 (previously 6.4-rc3)
v3 -> v4:
* Add to the meta-page:
- pages_lost / pages_read (allow to compute how full is the
ring-buffer)
- read (allow to compute how many entries can be read)
- A reader_page struct.
* Rename ring_buffer_meta_header -> ring_buffer_meta
* Rename ring_buffer_get_reader_page -> ring_buffer_map_get_reader_page
* Properly consume events on ring_buffer_map_get_reader_page() with
rb_advance_reader().
v2 -> v3:
* Remove data page list (for non-consuming read)
** Implies removing order > 0 meta-page
* Add a new meta page field ->read
* Rename ring_buffer_meta_page_header into ring_buffer_meta_header
v1 -> v2:
* Hide data_pages from the userspace struct
* Fix META_PAGE_MAX_PAGES
* Support for order > 0 meta-page
* Add missing page->mapping.
Vincent Donnefort (5):
ring-buffer: allocate sub-buffers with __GFP_COMP
ring-buffer: Introducing ring-buffer mapping functions
tracing: Allow user-space mapping of the ring-buffer
Documentation: tracing: Add ring-buffer mapping
