On Tue, 16 Sep 2025 10:36:57 -0700 Kalesh Singh <[email protected]> wrote:
> I completely agree with the principle that static tracepoints > shouldn't be used as markers if a dynamic probe will suffice. The > intent here is to avoid introducing overhead in the common case to > avoid regressing mmap, munmap, and other syscall latencies; while > still providing observability for the max vma_count exceeded failure > condition. > > The original centralized check (before previous review rounds) was > indeed in a dedicated function, exceeds_max_map_count(), where a > kprobe/fprobe could have been easily attached without impacting the > common path. This was changed due to previous review feedback to the > capacity based vma_count_remaining() which necessitated the check to > be done externally by the callers: > > https://lore.kernel.org/r/[email protected]/ > > Would you be ok with something like: > > trace_max_vma_count_exceeded(mm); > > TP_STRUCT__entry( > __field(unsigned int, mm_id) > __field(unsigned int vma_count) > ) > > mm_id would be the hash of the mm_struct ptr similar to rss_stat and > the vma_count is the current vma count (some syscalls have different > requirements on the capacity remaining: mremap requires 6 available > slots, other syscalls require 1). > BTW, why the hash of the mm pointer and not the pointer itself? We save pointers in lots of places, and if it is the pointer, you could use an eprobe to attache to the trace event to dereference its fields. -- Steve
