Messages in this thread | | | From | Alexei Starovoitov <> | Date | Mon, 2 Mar 2015 10:12:32 -0800 | Subject | Re: [PATCH 07/15] mm: Add ___GFP_NOTRACE |
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On Mon, Mar 2, 2015 at 10:03 AM, Tom Zanussi <tom.zanussi@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.zanussi@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.zanussi@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... 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. Can we keep kmalloc/kfree as-is and do something like if (in_tracepoint()) check inside ftrace_raw_kmalloc* ? so that kmalloc will be traced but calls to kmalloc from inside tracepoints will be automatically suppressed ?
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