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[scudo][standalone] Release smaller blocks less often

Authored by cryptoad on Jun 17 2020, 10:31 AM.

Description

[scudo][standalone] Release smaller blocks less often

Summary:
Releasing smaller blocks is costly and only yields significant
results when there is a large percentage of free bytes for a given
size class (see numbers below).

This CL introduces a couple of additional checks for sizes lower
than 256. First we want to make sure that there is enough free bytes,
relatively to the amount of allocated bytes. We are looking at 8X% to
9X% (smaller blocks require higher percentage). We also want to make
sure there has been enough activity with the freelist to make it
worth the time, so we now check that the bytes pushed to the freelist
is at least 1/16th of the allocated bytes for those classes.

Additionally, we clear batches before destroying them now - this
could have prevented some releases to occur (class id 0 rarely
releases anyway).

Here are the numbers, for about 1M allocations in multiple threads:

Size: 16
85% freed -> 0% released
86% freed -> 0% released
87% freed -> 0% released
88% freed -> 0% released
89% freed -> 0% released
90% freed -> 0% released
91% freed -> 0% released
92% freed -> 0% released
93% freed -> 0% released
94% freed -> 0% released
95% freed -> 0% released
96% freed -> 0% released
97% freed -> 2% released
98% freed -> 7% released
99% freed -> 27% released
Size: 32
85% freed -> 0% released
86% freed -> 0% released
87% freed -> 0% released
88% freed -> 0% released
89% freed -> 0% released
90% freed -> 0% released
91% freed -> 0% released
92% freed -> 0% released
93% freed -> 0% released
94% freed -> 0% released
95% freed -> 1% released
96% freed -> 3% released
97% freed -> 7% released
98% freed -> 17% released
99% freed -> 41% released
Size: 48
85% freed -> 0% released
86% freed -> 0% released
87% freed -> 0% released
88% freed -> 0% released
89% freed -> 0% released
90% freed -> 0% released
91% freed -> 0% released
92% freed -> 0% released
93% freed -> 0% released
94% freed -> 1% released
95% freed -> 3% released
96% freed -> 7% released
97% freed -> 13% released
98% freed -> 27% released
99% freed -> 52% released
Size: 64
85% freed -> 0% released
86% freed -> 0% released
87% freed -> 0% released
88% freed -> 0% released
89% freed -> 0% released
90% freed -> 0% released
91% freed -> 0% released
92% freed -> 1% released
93% freed -> 2% released
94% freed -> 3% released
95% freed -> 6% released
96% freed -> 11% released
97% freed -> 20% released
98% freed -> 35% released
99% freed -> 59% released
Size: 80
85% freed -> 0% released
86% freed -> 0% released
87% freed -> 0% released
88% freed -> 0% released
89% freed -> 0% released
90% freed -> 1% released
91% freed -> 1% released
92% freed -> 2% released
93% freed -> 4% released
94% freed -> 6% released
95% freed -> 10% released
96% freed -> 17% released
97% freed -> 26% released
98% freed -> 41% released
99% freed -> 64% released
Size: 96
85% freed -> 0% released
86% freed -> 0% released
87% freed -> 0% released
88% freed -> 0% released
89% freed -> 1% released
90% freed -> 1% released
91% freed -> 3% released
92% freed -> 4% released
93% freed -> 6% released
94% freed -> 10% released
95% freed -> 14% released
96% freed -> 21% released
97% freed -> 31% released
98% freed -> 47% released
99% freed -> 68% released
Size: 112
85% freed -> 0% released
86% freed -> 1% released
87% freed -> 1% released
88% freed -> 2% released
89% freed -> 3% released
90% freed -> 4% released
91% freed -> 6% released
92% freed -> 8% released
93% freed -> 11% released
94% freed -> 16% released
95% freed -> 22% released
96% freed -> 30% released
97% freed -> 40% released
98% freed -> 55% released
99% freed -> 74% released
Size: 128
85% freed -> 0% released
86% freed -> 1% released
87% freed -> 1% released
88% freed -> 2% released
89% freed -> 3% released
90% freed -> 4% released
91% freed -> 6% released
92% freed -> 8% released
93% freed -> 11% released
94% freed -> 16% released
95% freed -> 22% released
96% freed -> 30% released
97% freed -> 40% released
98% freed -> 55% released
99% freed -> 74% released
Size: 144
85% freed -> 1% released
86% freed -> 2% released
87% freed -> 3% released
88% freed -> 4% released
89% freed -> 6% released
90% freed -> 7% released
91% freed -> 10% released
92% freed -> 13% released
93% freed -> 17% released
94% freed -> 22% released
95% freed -> 28% released
96% freed -> 37% released
97% freed -> 47% released
98% freed -> 61% released
99% freed -> 78% released
Size: 160
85% freed -> 1% released
86% freed -> 2% released
87% freed -> 3% released
88% freed -> 4% released
89% freed -> 5% released
90% freed -> 7% released
91% freed -> 10% released
92% freed -> 13% released
93% freed -> 17% released
94% freed -> 22% released
95% freed -> 28% released
96% freed -> 37% released
97% freed -> 47% released
98% freed -> 61% released
99% freed -> 78% released
Size: 176
85% freed -> 2% released
86% freed -> 3% released
87% freed -> 4% released
88% freed -> 6% released
89% freed -> 7% released
90% freed -> 9% released
91% freed -> 12% released
92% freed -> 15% released
93% freed -> 20% released
94% freed -> 25% released
95% freed -> 32% released
96% freed -> 40% released
97% freed -> 51% released
98% freed -> 64% released
99% freed -> 80% released
Size: 192
85% freed -> 4% released
86% freed -> 5% released
87% freed -> 6% released
88% freed -> 8% released
89% freed -> 10% released
90% freed -> 13% released
91% freed -> 16% released
92% freed -> 20% released
93% freed -> 24% released
94% freed -> 30% released
95% freed -> 37% released
96% freed -> 45% released
97% freed -> 55% released
98% freed -> 68% released
99% freed -> 82% released
Size: 224
85% freed -> 8% released
86% freed -> 10% released
87% freed -> 12% released
88% freed -> 14% released
89% freed -> 17% released
90% freed -> 20% released
91% freed -> 23% released
92% freed -> 28% released
93% freed -> 33% released
94% freed -> 39% released
95% freed -> 46% released
96% freed -> 53% released
97% freed -> 63% released
98% freed -> 73% released
99% freed -> 85% released
Size: 240
85% freed -> 8% released
86% freed -> 10% released
87% freed -> 12% released
88% freed -> 14% released
89% freed -> 17% released
90% freed -> 20% released
91% freed -> 23% released
92% freed -> 28% released
93% freed -> 33% released
94% freed -> 39% released
95% freed -> 46% released
96% freed -> 54% released
97% freed -> 63% released
98% freed -> 73% released
99% freed -> 85% released

Reviewers: cferris, pcc, hctim, eugenis

Subscribers: #sanitizers, llvm-commits

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D82031

Details

Committed
cryptoadJul 16 2020, 9:44 AM
Differential Revision
D82031: [scudo][standalone] Release smaller blocks less often
Parents
rG3f05a4853ebd: [libc++abi] NFC: Fix indentation
Branches
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Tags
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