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This introduces palloc_aligned() and MemoryContextAllocAligned() which allow callers to obtain memory which is allocated to the given size and also aligned to the specified alignment boundary. The alignment boundaries may be any power-of-2 value. Currently, the alignment is capped at 2^26, however, we don't expect values anything like that large. The primary expected use case is to align allocations to perhaps CPU cache line size or to maybe I/O page size. Certain use cases can benefit from having aligned memory by either having better performance or more predictable performance. The alignment is achieved by requesting 'alignto' additional bytes from the underlying allocator function and then aligning the address that is returned to the requested alignment. This obviously does waste some memory, so alignments should be kept as small as what is required. It's also important to note that these alignment bytes eat into the maximum allocation size. So something like: palloc_aligned(MaxAllocSize, 64, 0); will not work as we cannot request MaxAllocSize + 64 bytes. Additionally, because we're just requesting the requested size plus the alignment requirements from the given MemoryContext, if that context is the Slab allocator, then since slab can only provide chunks of the size that's specified when the slab context is created, then this is not going to work. Slab will generate an error to indicate that the requested size is not supported. The alignment that is requested in palloc_aligned() is stored along with the allocated memory. This allows the alignment to remain intact through repalloc() calls. Author: Andres Freund, David Rowley Reviewed-by: Maxim Orlov, Andres Freund, John Naylor Discussion: https://postgr.es/m/CAApHDvpxLPUMV1mhxs6g7GNwCP6Cs6hfnYQL5ffJQTuFAuxt8A%40mail.gmail.com |
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| attoptcache.c | ||
| catcache.c | ||
| evtcache.c | ||
| inval.c | ||
| lsyscache.c | ||
| Makefile | ||
| meson.build | ||
| partcache.c | ||
| plancache.c | ||
| relcache.c | ||
| relfilenumbermap.c | ||
| relmapper.c | ||
| spccache.c | ||
| syscache.c | ||
| ts_cache.c | ||
| typcache.c | ||