On Mon, Mar 2, 2015 at 10:25 AM, Tom Zanussi <tom.zanu...@linux.intel.com> wrote: > 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).
would work, but kinda ugly, since we will pre-allocate a lot and may not be using it at all. > 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. not quite, I mean something like global kmalloc recursion flag. then kmalloc doesn't need to change. ftrace_raw_event_kmem_alloc() would use a flag inside ftrace_event_call struct or global recursion flag. -- 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/
