NFC: sizeclass: differentiate minimum step size and minimum allocation sizes #651
Conversation
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Like that? |
Is there a static_assert that the main is at least two pointers? |
Yes, two, sort of. Once directly by the configuration: And once by the |
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Out of curiosity, I did a little parameter sweeping with
It could be more interesting to do an analogous sweep on CHERI, where |
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Looks pretty noisy, but I can run some experiments on Monday |
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@nwf-msr would it make sense to add something like: if (SNMALLOC_BENCHMARK_INDIVIDUAL_CONFIGS)
foreach (STEP 8 16 32)
foreach (MIN 16 32 64)
if ((${STEP} EQUAL 8) AND (${MIN} EQUAL 64))
continue()
endif()
set(DEFINES "-DSNMALLOC_MIN_ALLOC_STEP_SIZE=${STEP}" "-DSNMALLOC_MIN_ALLOC_SIZE=${MIN}")
set(NAME "step-${STEP}-min-${MIN}")
add_shim(snmallocshim-${NAME} SHARED ${SHIM_FILES})
target_compile_definitions(snmallocshim-${NAME} PRIVATE ${DEFINES})
if (SNMALLOC_BUILD_TESTING)
make_tests(${NAME} ${DEFINES})
endif()
endforeach()
endforeach()
endif() # SNMALLOC_BENCHMARK_INDIVIDUAL_CONFIGSSo that we can rebuild the libraries for the test? |
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Here is running on my perf VM in Azure:
I dropped a couple of the noisier ones, but overall it doesn't have much change. |
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The sizeclass was already testing most of this, so just add the missing bits. Forgo some tests whose failure would have implied earlier failures. This moves the last dynamic call of size_to_sizeclass_const into tests (and so, too, to_exp_mant_const). sizeclasstable.h still contains a static call to compute NUM_SMALL_SIZECLASSES from MAX_SMALL_SIZECLASS_SIZE.
Only its _const sibling is used, and little at that, now that almost everything to do with sizes and size classes is table-driven.
This just means I don't need to remember to set a breakpoint on exit
Add support for a minimum allocation size that isn't the minimum step of the sizeclass table.
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Taking those two suggestions; thanks! Will merge as soon as CI's happy. |
No functional change intended yet. Just going through the exercise of separating
MIN_ALLOC_SIZE's two hats, but leaving the two at the same value.So why?
We think this might be useful, letting us use less space in #637 (by leaving
MIN_ALLOC_STEP_SIZEat16but raisingMIN_ALLOC_SIZEto32, meaning that sizeclasses 0 and 1 would not be allocable), but it might be more generally useful. It's also probably easier to review without all the rest of that mess at the same time. Speaking of review, as per usual, this might be best read in commit order rather than all at once, and the punchline is in the last commit.