On Mon, 2015-03-02 at 10:40 -0800, Alexei Starovoitov wrote: > 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. >
That's true but you have a user-defined map limit anyway, which you can adjust to minimize wastage. And allocating ahead of time also means you perturb the system less while actually tracing. Tom -- 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/
