Re:Custom Allocators Demystified
by dragontamer on Tuesday October 13, 2020 @06:25PM
(#24771010)
Hmmm... I'm pretty sure that when I hear "slab allocation", I imagine multiple sizes supported.
In the case of "fixed-size" allocations, you support all "smaller sizes" by returning a large size. Ex: malloc(4) returns a 64-byte block. malloc(20) returns a 64-byte block. malloc(64) returns a 64-byte block. malloc(65) causes assert( size < 64) fails, and your program exits.
malloc(65) would probably create a "new slab", supporting 128-byte blocks under a slab allocator. At least, based on how I normally hear the term used. malloc(34) may return a 64-byte block, but malloc(31) may return 32-byte block (supporting true sizes as power-of-2).
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The "slab allocator" discussed in the blogpost seems to be a fixed-size slab allocator though. So the blogpost's terminology doesn't match my own.
In the case of "fixed-size" allocations, you support all "smaller sizes" by returning a large size. Ex: malloc(4) returns a 64-byte block. malloc(20) returns a 64-byte block. malloc(64) returns a 64-byte block. malloc(65) causes assert( size < 64) fails, and your program exits.
malloc(65) would probably create a "new slab", supporting 128-byte blocks under a slab allocator. At least, based on how I normally hear the term used. malloc(34) may return a 64-byte block, but malloc(31) may return 32-byte block (supporting true sizes as power-of-2).
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The "slab allocator" discussed in the blogpost seems to be a fixed-size slab allocator though. So the blogpost's terminology doesn't match my own.