linux/kernel/events/ring_buffer.c, branch v6.14

perf: map pages in advance

2025-01-10T17:16:50Z

We are adjusting struct page to make it smaller, removing unneeded fields which correctly belong to struct folio. Two of those fields are page->index and page->mapping. Perf is currently making use of both of these. This is unnecessary. This patch eliminates this. Perf establishes its own internally controlled memory-mapped pages using vm_ops hooks. The first page in the mapping is the read/write user control page, and the rest of the mapping consists of read-only pages. The VMA is backed by kernel memory either from the buddy allocator or vmalloc depending on configuration. It is intended to be mapped read/write, but because it has a page_mkwrite() hook, vma_wants_writenotify() indicates that it should be mapped read-only. When a write fault occurs, the provided page_mkwrite() hook, perf_mmap_fault() (doing double duty handing faults as well) uses the vmf->pgoff field to determine if this is the first page, allowing for the desired read/write first page, read-only rest mapping. For this to work the implementation has to carefully work around faulting logic. When a page is write-faulted, the fault() hook is called first, then its page_mkwrite() hook is called (to allow for dirty tracking in file systems). On fault we set the folio's mapping in perf_mmap_fault(), this is because when do_page_mkwrite() is subsequently invoked, it treats a missing mapping as an indicator that the fault should be retried. We also set the folio's index so, given the folio is being treated as faux user memory, it correctly references its offset within the VMA. This explains why the mapping and index fields are used - but it's not necessary. We preallocate pages when perf_mmap() is called for the first time via rb_alloc(), and further allocate auxiliary pages via rb_aux_alloc() as needed if the mapping requires it. This allocation is done in the f_ops->mmap() hook provided in perf_mmap(), and so we can instead simply map all the memory right away here - there's no point in handling (read) page faults when we don't demand page nor need to be notified about them (perf does not). This patch therefore changes this logic to map everything when the mmap() hook is called, establishing a PFN map. It implements vm_ops->pfn_mkwrite() to provide the required read/write vs. read-only behaviour, which does not require the previously implemented workarounds. While it is not ideal to use a VM_PFNMAP here, doing anything else will result in the page_mkwrite() hook need to be provided, which requires the same page->mapping hack this patch seeks to undo. It will also result in the pages being treated as folios and placed on the rmap, which really does not make sense for these mappings. Semantically it makes sense to establish this as some kind of special mapping, as the pages are managed by perf and are not strictly user pages, but currently the only means by which we can do so functionally while maintaining the required R/W and R/O behaviour is a PFN map. There should be no change to actual functionality as a result of this change. Signed-off-by: Lorenzo Stoakes Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20250103153151.124163-1-lorenzo.stoakes@oracle.com

perf/aux: Fix AUX buffer serialization

2024-09-04T16:22:56Z

Ole reported that event->mmap_mutex is strictly insufficient to serialize the AUX buffer, add a per RB mutex to fully serialize it. Note that in the lock order comment the perf_event::mmap_mutex order was already wrong, that is, it nesting under mmap_lock is not new with this patch. Fixes: 45bfb2e50471 ("perf: Add AUX area to ring buffer for raw data streams") Reported-by: Ole Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar

perf: Make rb_alloc_aux() return an error immediately if nr_pages <= 0

2024-07-04T14:00:23Z

rb_alloc_aux() should not be called with nr_pages <= 0. Make it more robust and readable by returning an error immediately in that case. Signed-off-by: Adrian Hunter Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20240624201101.60186-8-adrian.hunter@intel.com

perf: Fix default aux_watermark calculation

2024-07-04T14:00:23Z

The default aux_watermark is half the AUX area buffer size. In general, on a 64-bit architecture, the AUX area buffer size could be a bigger than fits in a 32-bit type, but the calculation does not allow for that possibility. However the aux_watermark value is recorded in a u32, so should not be more than U32_MAX either. Fix by doing the calculation in a correctly sized type, and limiting the result to U32_MAX. Fixes: d68e6799a5c8 ("perf: Cap allocation order at aux_watermark") Signed-off-by: Adrian Hunter Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20240624201101.60186-7-adrian.hunter@intel.com

perf/ring_buffer: Trigger IO signals for watermark_wakeup

2024-04-14T20:26:32Z

perf_output_wakeup() already marks the perf event fd available for polling. Trigger IO signals with FASYNC too. Signed-off-by: Kyle Huey Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20240413141618.4160-3-khuey@kylehuey.com

mm, treewide: rename MAX_ORDER to MAX_PAGE_ORDER

2024-01-08T23:27:15Z

commit 23baf831a32c ("mm, treewide: redefine MAX_ORDER sanely") has changed the definition of MAX_ORDER to be inclusive. This has caused issues with code that was not yet upstream and depended on the previous definition. To draw attention to the altered meaning of the define, rename MAX_ORDER to MAX_PAGE_ORDER. Link: https://lkml.kernel.org/r/20231228144704.14033-2-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov Cc: Linus Torvalds Signed-off-by: Andrew Morton

perf/core: Bail out early if the request AUX area is out of bound

2023-09-12T15:46:31Z

When perf-record with a large AUX area, e.g 4GB, it fails with: #perf record -C 0 -m ,4G -e arm_spe_0// -- sleep 1 failed to mmap with 12 (Cannot allocate memory) and it reveals a WARNING with __alloc_pages(): ------------[ cut here ]------------ WARNING: CPU: 44 PID: 17573 at mm/page_alloc.c:5568 __alloc_pages+0x1ec/0x248 Call trace: __alloc_pages+0x1ec/0x248 __kmalloc_large_node+0xc0/0x1f8 __kmalloc_node+0x134/0x1e8 rb_alloc_aux+0xe0/0x298 perf_mmap+0x440/0x660 mmap_region+0x308/0x8a8 do_mmap+0x3c0/0x528 vm_mmap_pgoff+0xf4/0x1b8 ksys_mmap_pgoff+0x18c/0x218 __arm64_sys_mmap+0x38/0x58 invoke_syscall+0x50/0x128 el0_svc_common.constprop.0+0x58/0x188 do_el0_svc+0x34/0x50 el0_svc+0x34/0x108 el0t_64_sync_handler+0xb8/0xc0 el0t_64_sync+0x1a4/0x1a8 'rb->aux_pages' allocated by kcalloc() is a pointer array which is used to maintains AUX trace pages. The allocated page for this array is physically contiguous (and virtually contiguous) with an order of 0..MAX_ORDER. If the size of pointer array crosses the limitation set by MAX_ORDER, it reveals a WARNING. So bail out early with -ENOMEM if the request AUX area is out of bound, e.g.: #perf record -C 0 -m ,4G -e arm_spe_0// -- sleep 1 failed to mmap with 12 (Cannot allocate memory) Signed-off-by: Shuai Xue Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar

perf/ring_buffer: Use local_try_cmpxchg in __perf_output_begin

2023-07-10T07:52:36Z

Use local_try_cmpxchg instead of local_cmpxchg (*ptr, old, new) == old in __perf_output_begin. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg fails. There is no need to re-read the value in the loop. No functional change intended. Signed-off-by: Uros Bizjak Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20230708090048.63046-2-ubizjak@gmail.com

mm, treewide: redefine MAX_ORDER sanely

2023-04-06T02:42:46Z

MAX_ORDER currently defined as number of orders page allocator supports: user can ask buddy allocator for page order between 0 and MAX_ORDER-1. This definition is counter-intuitive and lead to number of bugs all over the kernel. Change the definition of MAX_ORDER to be inclusive: the range of orders user can ask from buddy allocator is 0..MAX_ORDER now. [kirill@shutemov.name: fix min() warning] Link: https://lkml.kernel.org/r/20230315153800.32wib3n5rickolvh@box [akpm@linux-foundation.org: fix another min_t warning] [kirill@shutemov.name: fixups per Zi Yan] Link: https://lkml.kernel.org/r/20230316232144.b7ic4cif4kjiabws@box.shutemov.name [akpm@linux-foundation.org: fix underlining in docs] Link: https://lore.kernel.org/oe-kbuild-all/202303191025.VRCTk6mP-lkp@intel.com/ Link: https://lkml.kernel.org/r/20230315113133.11326-11-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov Reviewed-by: Michael Ellerman [powerpc] Cc: "Kirill A. Shutemov" Cc: Zi Yan Signed-off-by: Andrew Morton

perf/core: fix MAX_ORDER usage in rb_alloc_aux_page()

2023-04-06T02:42:45Z

MAX_ORDER is not inclusive: the maximum allocation order buddy allocator can deliver is MAX_ORDER-1. Fix MAX_ORDER usage in rb_alloc_aux_page(). Link: https://lkml.kernel.org/r/20230315113133.11326-7-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Arnaldo Carvalho de Melo Cc: Mark Rutland Cc: Alexander Shishkin Cc: Jiri Olsa Cc: Namhyung Kim Cc: Ian Rogers Cc: Adrian Hunter Signed-off-by: Andrew Morton