879e76a9e5
This provides in-place expansion of huge allocations when the end of the
allocation is at the end of the sbrk heap. There's already the ability
to extend in-place via recycled chunks but this handles the initial
growth of the heap via repeated vector / string reallocations.
A possible future extension could allow realloc to go from the following:
| huge allocation | recycled chunks |
^ dss_end
To a larger allocation built from recycled *and* new chunks:
| huge allocation |
^ dss_end
Doing that would involve teaching the chunk recycling code to request
new chunks to satisfy the request. The chunk_dss code wouldn't require
any further changes.
#include <stdlib.h>
int main(void) {
size_t chunk = 4 * 1024 * 1024;
void *ptr = NULL;
for (size_t size = chunk; size < chunk * 128; size *= 2) {
ptr = realloc(ptr, size);
if (!ptr) return 1;
}
}
dss:secondary: 0.083s
dss:primary: 0.083s
After:
dss:secondary: 0.083s
dss:primary: 0.003s
The dss heap grows in the upwards direction, so the oldest chunks are at
the low addresses and they are used first. Linux prefers to grow the
mmap heap downwards, so the trick will not work in the *current* mmap
chunk allocator as a huge allocation will only be at the top of the heap
in a contrived case.
40 lines
1.2 KiB
C
40 lines
1.2 KiB
C
/******************************************************************************/
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#ifdef JEMALLOC_H_TYPES
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typedef enum {
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dss_prec_disabled = 0,
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dss_prec_primary = 1,
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dss_prec_secondary = 2,
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dss_prec_limit = 3
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} dss_prec_t;
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#define DSS_PREC_DEFAULT dss_prec_secondary
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#define DSS_DEFAULT "secondary"
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#endif /* JEMALLOC_H_TYPES */
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/******************************************************************************/
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#ifdef JEMALLOC_H_STRUCTS
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extern const char *dss_prec_names[];
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#endif /* JEMALLOC_H_STRUCTS */
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/******************************************************************************/
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#ifdef JEMALLOC_H_EXTERNS
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dss_prec_t chunk_dss_prec_get(void);
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bool chunk_dss_prec_set(dss_prec_t dss_prec);
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void *chunk_alloc_dss(void *new_addr, size_t size, size_t alignment,
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bool *zero);
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bool chunk_in_dss(void *chunk);
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bool chunk_dss_boot(void);
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void chunk_dss_prefork(void);
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void chunk_dss_postfork_parent(void);
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void chunk_dss_postfork_child(void);
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#endif /* JEMALLOC_H_EXTERNS */
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/******************************************************************************/
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#ifdef JEMALLOC_H_INLINES
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#endif /* JEMALLOC_H_INLINES */
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/******************************************************************************/
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