On Mon, 2015-03-02 at 10:12 -0800, Alexei Starovoitov wrote: > On Mon, Mar 2, 2015 at 10:03 AM, Tom Zanussi > <tom.zanu...@linux.intel.com> wrote: > > On Mon, 2015-03-02 at 09:58 -0800, Alexei Starovoitov wrote: > >> On Mon, Mar 2, 2015 at 8:46 AM, Tom Zanussi <tom.zanu...@linux.intel.com> > >> wrote: > >> > On Mon, 2015-03-02 at 11:37 -0500, Steven Rostedt wrote: > >> >> On Mon, 2 Mar 2015 10:01:00 -0600 > >> >> Tom Zanussi <tom.zanu...@linux.intel.com> wrote: > >> >> > >> >> > Add a gfp flag that allows kmalloc() et al to be used in tracing > >> >> > functions. > >> >> > > >> >> > The problem with using kmalloc for tracing is that the tracing > >> >> > subsystem should be able to trace kmalloc itself, which it can't do > >> >> > directly because of paths like kmalloc()->trace_kmalloc()->kmalloc() > >> >> > or kmalloc()->trace_mm_page_alloc()->kmalloc(). > >> >> > >> >> This part I don't like at all. Why can't the memory be preallocated > >> >> when the hist is created (the echo 'hist:...')? > >> >> > >> > > >> > Yeah, I didn't like it either. My original version did exactly what you > >> > suggest and preallocated an array of entries to 'allocate' from in order > >> > to avoid the problem. > >> > > >> > But I wanted to attempt to use the bpf_map directly, which already uses > >> > kmalloc internally. My fallback in case this wouldn't fly, which it > >> > obviously won't, would be to add an option to have the bpf_map code > >> > preallocate a maximum number of entries or pass in a client-owned array > >> > for the purpose. I'll do that if I don't hear any better ideas.. > >> > >> Tom, I'm still reading through the patch set. > >> Quick comment for the above. > >> Currently there are two map types: array and hash. > >> array type is pre-allocating all memory at map creation time. > >> hash is allocating on demand. > > > > OK, so would it make sense to do the same for the hash type, or at least > > add an option that does that? > > I'm not sure what would be the meaning of hash map that has all > elements pre-allocated...
The idea would be that instead of getting your individually kmalloc'ed elements on-demand from kmalloc while in the handler, you'd get them from a pool you've pre-allocated when you set up the table. This could be from a list of individual entries you've already kmalloc'ed ahead of time, or from an array of n * sizeof(entry). This would also allow you to avoid GFP_ATOMIC for those. > As I'm reading your cover letter, I agree, we need to find a way > to call kmalloc_notrace-like from tracepoints. > Not sure that patch 8 style of duplicating the functions is clean. No, it's horrible, but it does the job without changing the normal path at all. > Can we keep kmalloc/kfree as-is and do something like > if (in_tracepoint()) check inside ftrace_raw_kmalloc* ? Yeah, that's essentially what TP_CONDITION() in patch 8 (Make kmem memory allocation tracepoints conditional) does. Tom > so that kmalloc will be traced but calls to kmalloc from inside > tracepoints will be automatically suppressed ? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/