On Wed, 26 Oct 2022 10:52:18 +0530 Gautam Menghani <gautammenghani201@xxxxxxxxx> wrote: Ideally we want the trace event structure to be as packed as possible to not waste space on the ring buffer. > + TP_ARGS(mm, hpage, index, is_shmem, addr, file, nr, result), > + TP_STRUCT__entry( > + __field(struct mm_struct *, mm) 4 / 8 bytes (depending on 32 bit or 64 bit arch) > + __field(unsigned long, hpfn) 4 / 8 bytes The two above is fine. > + __field(pgoff_t, index) 4 / 8 bytes > + __field(bool, is_shmem) 4 bytes (or less) > + __field(unsigned long, addr) 4 / 8 bytes > + __string(filename, file->f_path.dentry->d_iname) 4 bytes > + __field(int, nr) 4 bytes > + __field(int, result) 4 bytes For best packing, it's best to keep long / pointers together, and ints and bools together (or paired). On 64 bit archs, there is likely to be a 4 byte hole between is_shmem and addr. > + ), > + Better to have it be: TP_STRUCT__entry( __field(struct mm_struct *, mm) __field(unsigned long, hpfn) __field(pgoff_t, index) __field(unsigned long, addr) __field(bool, is_shmem) __string(filename, file->f_path.dentry->d_iname) __field(int, nr) __field(int, result) ), Where I swapped is_shmem and addr. -- Steve
