Messages in this thread | | | Date | Fri, 4 Apr 2008 12:40:22 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [PATCH] relay: add buffer-only functionality, allowing for early kernel tracing |
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* Eduard - Gabriel Munteanu (eduard.munteanu@linux360.ro) wrote: > On Fri, 4 Apr 2008 12:06:23 -0400 > Mathieu Desnoyers <compudj@krystal.dyndns.org> wrote: > > > I like this :) But could we trace event sooner if we did not depend on > > vmalloc to allocate the buffers ? > > > > I am thinking of receiving a kernel parameter that would reserve a > > buffer in the linear kernel mapping (kmalloc ?), or to compile-in a > > static buffer, which could be used by relay instead of the vmalloc'd > > buffer. That would permit to trace the memory allocator and some other > > very early stuff. Basically, relay would have it's "memory pool" to > > manage and would do its allocations from this fixed buffer. No free > > would be required. > > > > Mathieu > > Sure. I'm doing this as part of my GSoC application (well, I haven't > been accepted yet). I had also proposed this to Pekka Enberg, my > mentor, but he was reluctant to hack the relay code more invasively. Now > that you agree with this, I'll work on it. > > kmalloc() doesn't work before kmem_cache_init() and relay code uses > kmalloc(), not vmalloc(), IIRC. >
It currently uses both :
It uses alloc_page and vmap to allocate the buffers and it uses kzalloc/kmalloc to allocate the relay structures.
> I would go another way. Have the relay client call __get_free_pages() > or similar function, allocate the buffer and pass it on to a variant of > relay_open(), let's name it relay_early_open(). __get_free_pages() can > be used before kmem_cache_init() as far as I know. No free is required, > since early tracing code implies it's built into the kernel and not as > a module. What do you say? >
Then I guess we would depend on page_alloc_init(). It's not that bad, but I guess the question is : do we prefer to let users specify the buffer size to reserve for tracing on the kernel command line (that would require __get_free_pages()) or do we compile-in a static buffer size, which can be specified in the kernel configuration. I think providing both could be an option : flexibility _and_ *very* early tracing.
So making this relay interface flexible enough to receive a buffer either reserved by __get_free_pages() or a static buffer seems like a good compromise. It would also have to receive the buffer size from the caller.
> Will you merge this or wait until I finish the very early tracing stuff? >
As far as I am concerned, I can only merge this in the LTTng project to try it. I've added Tom Zanussi, the author of relay, who might have some ideas to share with us. I would wait until we have a more precise idea of the API before I modify LTTng to start using it.
Regards,
Mathieu
> Cheers, > Eduard >
-- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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