[PATCH 1/7] perf mmap: Fix perf backward recording

perf record backward recording doesn't work as we expected: it never overwrite when ring buffer full. Test: (Run a busy printing task background like this: while True: print 123 send SIGUSR2 to perf to capture snapshot.) # ./perf record --overwrite -e raw_syscalls:sys_enter -e

[PATCH 1/7] perf mmap: Fix perf backward recording

perf record backward recording doesn't work as we expected: it never overwrite when ring buffer full. Test: (Run a busy printing task background like this: while True: print 123 send SIGUSR2 to perf to capture snapshot.) # ./perf record --overwrite -e raw_syscalls:sys_enter -e