hashtable: fix dismissHashtable madvise size#3533
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Signed-off-by: DaeMyung Kang <charsyam@gmail.com>
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## unstable #3533 +/- ##
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+ Coverage 76.40% 76.45% +0.05%
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Files 159 159
Lines 79851 79851
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+ Hits 61008 61049 +41
+ Misses 18843 18802 -41
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sarthakaggarwal97
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The bug was in dismissHashtable(), which computes the size passed to zmadvise_dontneed() for the top-level hashtable tables. ht->tables[i] points to a contiguous array of bucket objects, but the code used sizeof(bucket *) instead of sizeof(bucket) when calculating the length. That means it treated the allocation like an array of pointers rather than an array of buckets. As a result, the advised range was much smaller than the actual table allocation. On 64-bit builds, bucket is 64 bytes while bucket * is 8 bytes, so only about one eighth of the table was covered. This does not usually break correctness, but it defeats the purpose of the function: after a fork, we want to tell the kernel that the hashtable pages are no longer needed so we reduce copy-on-write overhead. With the wrong size, most of the table memory was never included in that hint. The fix is to use sizeof(bucket) so the full top-level bucket array is passed to zmadvise_dontneed(). Signed-off-by: DaeMyung Kang <charsyam@gmail.com>
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…-io#3533, valkey-io#3557, valkey-io#3548, valkey-io#3554, valkey-io#3503) Signed-off-by: Sarthak Aggarwal <sarthagg@amazon.com>
madolson
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The bug was in dismissHashtable(), which computes the size passed to zmadvise_dontneed() for the top-level hashtable tables. ht->tables[i] points to a contiguous array of bucket objects, but the code used sizeof(bucket *) instead of sizeof(bucket) when calculating the length. That means it treated the allocation like an array of pointers rather than an array of buckets. As a result, the advised range was much smaller than the actual table allocation. On 64-bit builds, bucket is 64 bytes while bucket * is 8 bytes, so only about one eighth of the table was covered. This does not usually break correctness, but it defeats the purpose of the function: after a fork, we want to tell the kernel that the hashtable pages are no longer needed so we reduce copy-on-write overhead. With the wrong size, most of the table memory was never included in that hint. The fix is to use sizeof(bucket) so the full top-level bucket array is passed to zmadvise_dontneed(). Signed-off-by: DaeMyung Kang <charsyam@gmail.com>
sarthakaggarwal97
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…key-io#3359, valkey-io#3533, valkey-io#3557) Signed-off-by: Sarthak Aggarwal <sarthagg@amazon.com>
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The bug was in dismissHashtable(), which computes the size passed to zmadvise_dontneed() for the top-level hashtable
tables.
ht->tables[i] points to a contiguous array of bucket objects, but the code used sizeof(bucket *) instead of
sizeof(bucket) when calculating the length. That means it treated the allocation like an array of pointers rather than an
array of buckets.
As a result, the advised range was much smaller than the actual table allocation. On 64-bit builds, bucket is 64 bytes
while bucket * is 8 bytes, so only about one eighth of the table was covered. This does not usually break correctness,
but it defeats the purpose of the function: after a fork, we want to tell the kernel that the hashtable pages are no
longer needed so we reduce copy-on-write overhead. With the wrong size, most of the table memory was never included in
that hint.
The fix is to use sizeof(bucket) so the full top-level bucket array is passed to zmadvise_dontneed().