Suppress all-zero compressibility columns in heap profiles. - #1021
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MakeProfileProto advertises the space_compressed and zero_space sample types whenever compressibility collection is enabled, even when not a single sample was analyzed. Every sample then carries a literal 0 for both, which is indistinguishable downstream from a heap that was measured and found to hold no compressible or zero bytes. A consumer computing savings as (resident + swapped) - compressed scores such a profile as 100% compressible. Root Cause: the decision to emit the columns was derived from FLAGS_heapz_collect_compressibility alone, which says the analyzer is allowed to run, not that it ever produced a result. Analysis is skipped whenever residency reports nothing for the span, span_start_address is null, requested_size is 0, or CompressionAnalyzer::Analyze fails, and SampleMergedData::compressed_size and ::zero_size then keep their zero initializers. Have the merge report whether the analyzer ever succeeded and add the two sample types only when it did. A profile with no measurements now looks exactly like one from a binary that does not collect compressibility at all: the columns are absent rather than uniformly zero. PiperOrigin-RevId: 984957126
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Suppress all-zero compressibility columns in heap profiles.
MakeProfileProto advertises the space_compressed and zero_space sample types
whenever compressibility collection is enabled, even when not a single sample
was analyzed. Every sample then carries a literal 0 for both, which is
indistinguishable downstream from a heap that was measured and found to hold
no compressible or zero bytes. A consumer computing savings as
(resident + swapped) - compressed scores such a profile as 100% compressible.
Root Cause: the decision to emit the columns was derived from
FLAGS_heapz_collect_compressibility alone, which says the analyzer is allowed
to run, not that it ever produced a result. Analysis is skipped whenever
residency reports nothing for the span, span_start_address is null,
requested_size is 0, or CompressionAnalyzer::Analyze fails, and
SampleMergedData::compressed_size and ::zero_size then keep their zero
initializers.
Have the merge report whether the analyzer ever succeeded and add the two
sample types only when it did. A profile with no measurements now looks
exactly like one from a binary that does not collect compressibility at all:
the columns are absent rather than uniformly zero.