On 08/15/2012 12:45 PM, Michael Roth wrote: > Currently, when parsing a stream of tokens we make a copy of the token > list at the beginning of each level of recursion so that we do not > modify the original list in cases where we need to fall back to an > earlier state. > > In the worst case, we will only read 1 or 2 tokens off the list before > recursing again, which means an upper bound of roughly N^2 token allocations. > > For a "reasonably" sized QMP request (in this a QMP representation of > cirrus_vga's device state, generated via QIDL, being passed in via > qom-set), this caused my 16GB's of memory to be exhausted before any > noticeable progress was made by the parser. > > This patch works around the issue by using single copy of the token list > in the form of an indexable array so that we can save/restore state by > manipulating indices. > > A subsequent commit adds a "large_dict" test case which exhibits the > same behavior as above. With this patch applied the test case successfully > completes in under a second. > > Tested with valgrind, make check, and QMP. > > Signed-off-by: Michael Roth <mdr...@linux.vnet.ibm.com> > --- > json-parser.c | 230 > +++++++++++++++++++++++++++++++++++---------------------- > 1 file changed, 142 insertions(+), 88 deletions(-)
I'm not the most familiar with this code, so take my review with a grain
of salt, but I read through it and the transformation looks sane (and my
non-code findings from v2 were fixed).
Reviewed-by: Eric Blake <ebl...@redhat.com>
> +static JSONParserContext parser_context_save(JSONParserContext *ctxt)
> +{
> + JSONParserContext saved_ctxt = {0};
> + saved_ctxt.tokens.pos = ctxt->tokens.pos;
> + saved_ctxt.tokens.count = ctxt->tokens.count;
> + saved_ctxt.tokens.buf = ctxt->tokens.buf;
Is it any simpler to condense 3 lines to 1:
saved_cts.tokens = ctxt->tokens;
> + return saved_ctxt;
> +}
> +
> +static void parser_context_restore(JSONParserContext *ctxt,
> + JSONParserContext saved_ctxt)
> +{
> + ctxt->tokens.pos = saved_ctxt.tokens.pos;
> + ctxt->tokens.count = saved_ctxt.tokens.count;
> + ctxt->tokens.buf = saved_ctxt.tokens.buf;
and again, ctxt->tokens = saved_ctxt.tokens;
--
Eric Blake ebl...@redhat.com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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