| Message ID | 20240628104611.1443542-1-vdonnefort@google.com (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
| Series | [v2] ring-buffer: Align meta-page to sub-buffers for improved TLB usage | expand |
On Fri, 28 Jun 2024 11:46:11 +0100 Vincent Donnefort <vdonnefort@google.com> wrote: > This is based on the mm-unstable branch [1] as it depends on David's work [2] > for allowing the zero-page in vm_insert_page(). > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git > [2] https://lore.kernel.org/all/20240522125713.775114-1-david@redhat.com I'll hold off to 6.12 merge window before pushing this. So that the above will be guaranteed to be there. -- Steve
On Fri, 28 Jun 2024 11:46:11 +0100 Vincent Donnefort <vdonnefort@google.com> wrote: > diff --git a/tools/testing/selftests/ring-buffer/map_test.c b/tools/testing/selftests/ring-buffer/map_test.c > index a9006fa7097e..4bb0192e43f3 100644 > --- a/tools/testing/selftests/ring-buffer/map_test.c > +++ b/tools/testing/selftests/ring-buffer/map_test.c > @@ -228,6 +228,20 @@ TEST_F(map, data_mmap) > data = mmap(NULL, data_len, PROT_READ, MAP_SHARED, > desc->cpu_fd, meta_len); > ASSERT_EQ(data, MAP_FAILED); > + > + /* Verify meta-page padding */ > + if (desc->meta->meta_page_size > getpagesize()) { > + void *addr; > + > + data_len = desc->meta->meta_page_size; > + data = mmap(NULL, data_len, > + PROT_READ, MAP_SHARED, desc->cpu_fd, 0); > + ASSERT_NE(data, MAP_FAILED); > + > + addr = (void *)((unsigned long)data + getpagesize()); > + ASSERT_EQ(*((int *)addr), 0); Should we make this a test that the entire page is zero? for (int i = desc->meta->meta_struct_len; i < desc->meta->meta_page_size; i += sizeof(int)) ASSERT_EQ(((int *)data)[i], 0); ? > + munmap(data, data_len); > + } > } Also, looking at the init, if for some reason (I highly doubt it may happen) that the meta_struct_len becomes bigger than page_size, we should update the init section to: /* Handle the case where meta_struct_len is greater than page size */ if (page_size < desc->meta->meta_struct_len) { /* meta_page_size is >= meta_struct_len */ page_size = desc->meta->meta_page_size; munmap(desc->meta, page_size); map = mmap(NULL, page_size, PROT_READ, MAP_SHARED, desc->cpu_fd, 0); if (map == MAP_FAILED) return -errno; desc->meta = (struct trace_buffer_meta *)map; } -- Steve
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 7345a8b625fb..c1116e76fe17 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -6148,10 +6148,10 @@ static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer, /* install subbuf ID to kern VA translation */ cpu_buffer->subbuf_ids = subbuf_ids; - meta->meta_page_size = PAGE_SIZE; meta->meta_struct_len = sizeof(*meta); meta->nr_subbufs = nr_subbufs; meta->subbuf_size = cpu_buffer->buffer->subbuf_size + BUF_PAGE_HDR_SIZE; + meta->meta_page_size = meta->subbuf_size; rb_update_meta_page(cpu_buffer); } @@ -6238,6 +6238,12 @@ static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer, !(vma->vm_flags & VM_MAYSHARE)) return -EPERM; + subbuf_order = cpu_buffer->buffer->subbuf_order; + subbuf_pages = 1 << subbuf_order; + + if (subbuf_order && pgoff % subbuf_pages) + return -EINVAL; + /* * Make sure the mapping cannot become writable later. Also tell the VM * to not touch these pages (VM_DONTCOPY | VM_DONTEXPAND). @@ -6247,11 +6253,8 @@ static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer, lockdep_assert_held(&cpu_buffer->mapping_lock); - subbuf_order = cpu_buffer->buffer->subbuf_order; - subbuf_pages = 1 << subbuf_order; - nr_subbufs = cpu_buffer->nr_pages + 1; /* + reader-subbuf */ - nr_pages = ((nr_subbufs) << subbuf_order) - pgoff + 1; /* + meta-page */ + nr_pages = ((nr_subbufs + 1) << subbuf_order) - pgoff; /* + meta-page */ vma_pages = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT; if (!vma_pages || vma_pages > nr_pages) @@ -6264,20 +6267,24 @@ static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer, return -ENOMEM; if (!pgoff) { + unsigned long meta_page_padding; + pages[p++] = virt_to_page(cpu_buffer->meta_page); /* - * TODO: Align sub-buffers on their size, once - * vm_insert_pages() supports the zero-page. + * Pad with the zero-page to align the meta-page with the + * sub-buffers. */ - } else { - /* Skip the meta-page */ - pgoff--; + meta_page_padding = subbuf_pages - 1; + while (meta_page_padding-- && p < nr_pages) { + unsigned long __maybe_unused zero_addr = + vma->vm_start + (PAGE_SIZE * p); - if (pgoff % subbuf_pages) { - err = -EINVAL; - goto out; + pages[p++] = ZERO_PAGE(zero_addr); } + } else { + /* Skip the meta-page */ + pgoff -= subbuf_pages; s += pgoff / subbuf_pages; } diff --git a/tools/testing/selftests/ring-buffer/map_test.c b/tools/testing/selftests/ring-buffer/map_test.c index a9006fa7097e..4bb0192e43f3 100644 --- a/tools/testing/selftests/ring-buffer/map_test.c +++ b/tools/testing/selftests/ring-buffer/map_test.c @@ -228,6 +228,20 @@ TEST_F(map, data_mmap) data = mmap(NULL, data_len, PROT_READ, MAP_SHARED, desc->cpu_fd, meta_len); ASSERT_EQ(data, MAP_FAILED); + + /* Verify meta-page padding */ + if (desc->meta->meta_page_size > getpagesize()) { + void *addr; + + data_len = desc->meta->meta_page_size; + data = mmap(NULL, data_len, + PROT_READ, MAP_SHARED, desc->cpu_fd, 0); + ASSERT_NE(data, MAP_FAILED); + + addr = (void *)((unsigned long)data + getpagesize()); + ASSERT_EQ(*((int *)addr), 0); + munmap(data, data_len); + } } FIXTURE(snapshot) {
Previously, the mapped ring-buffer layout caused misalignment between the meta-page and sub-buffers when the sub-buffer size was not a multiple of PAGE_SIZE. This prevented hardware with larger TLB entries from utilizing them effectively. Add a padding with the zero-page between the meta-page and sub-buffers. Also update the ring-buffer map_test to verify that padding. Signed-off-by: Vincent Donnefort <vdonnefort@google.com> -- This is based on the mm-unstable branch [1] as it depends on David's work [2] for allowing the zero-page in vm_insert_page(). [1] https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git [2] https://lore.kernel.org/all/20240522125713.775114-1-david@redhat.com v1 -> v2: * Fix unsequenced modification and access to 'p' (s390 build) base-commit: c65920c76a977c2b73c3a8b03b4c0c00cc1285ed