Hi All,

Request your help in understanding the below program, with the below program I can allocate 8589934592(8GB) it prints the length 8589934592(8GB) where as my laptop has only 4 GB so the confusion is that how can this program allocate 8GB RAM when I have only 4GB of RAM installed

import std.algorithm.comparison : max;
import std.experimental.allocator.building_blocks.allocator_list : AllocatorList;
import std.experimental.allocator.building_blocks.bucketizer;
import std.experimental.allocator.building_blocks.free_list : FreeList;
import std.experimental.allocator.building_blocks.region : Region;
import std.experimental.allocator.building_blocks.segregator;
import std.experimental.allocator.common : unbounded;
import std.experimental.allocator.mallocator : Mallocator;
import std.stdio: writeln;

void main () {
alias FList = FreeList!(Mallocator, 0, unbounded);
alias A = Segregator!(
      8, FreeList!(Mallocator, 0, 8),
      128, Bucketizer!(FList, 1, 128, 16),
      256, Bucketizer!(FList, 129, 256, 32),
      512, Bucketizer!(FList, 257, 512, 64),
      1024, Bucketizer!(FList, 513, 1024, 128),
      2048, Bucketizer!(FList, 1025, 2048, 256),
      3584, Bucketizer!(FList, 2049, 3584, 512),
      4097 * 1024, AllocatorList!(n => Region!Mallocator(max(n, 1024 * 4096))),
      Mallocator
);
A tuMalloc;
auto c = tuMalloc.allocate(8589934592);  // 8GB
writeln(c.length);                       // output: 8589934592
tuMalloc.deallocate(c);
}

From,
Vino

On Saturday, 2 December 2023 at 19:13:18 UTC, Vino B wrote:

import std.algorithm.comparison : max;
import std.experimental.allocator.building_blocks.allocator_list : AllocatorList;
import std.experimental.allocator.building_blocks.bucketizer;
import std.experimental.allocator.building_blocks.free_list : FreeList;
import std.experimental.allocator.building_blocks.region : Region;
import std.experimental.allocator.building_blocks.segregator;
import std.experimental.allocator.common : unbounded;
import std.experimental.allocator.mallocator : Mallocator;
import std.stdio: writeln;

void main () {
alias FList = FreeList!(Mallocator, 0, unbounded);
alias A = Segregator!(
      8, FreeList!(Mallocator, 0, 8),
      128, Bucketizer!(FList, 1, 128, 16),
      256, Bucketizer!(FList, 129, 256, 32),
      512, Bucketizer!(FList, 257, 512, 64),
      1024, Bucketizer!(FList, 513, 1024, 128),
      2048, Bucketizer!(FList, 1025, 2048, 256),
      3584, Bucketizer!(FList, 2049, 3584, 512),
      4097 * 1024, AllocatorList!(n => Region!Mallocator(max(n, 1024 * 4096))),
      Mallocator
);
A tuMalloc;
auto c = tuMalloc.allocate(8589934592);  // 8GB
writeln(c.length);                       // output: 8589934592
tuMalloc.deallocate(c);
}

This is normal behavior on linux, it's called overcommit memory, i think it was meant to allow things like fork() to work properly

https://stackoverflow.com/a/7504354

On Saturday, 2 December 2023 at 19:13:18 UTC, Vino B wrote:

Welcome to the wonderful world of virtual memory.

Virtual memory size != physical memory size

This nothing to do with D programming language but how the OS manage the memory.