Custom allocator on top of jemalloc

[Jason Evans]

On Jan 20, 2015, at 5:17 AM, SNL <snl20465 at gmail.com> wrote:
> Here is what I am doing currently:
> 
> 1. I am trying to carve out 10 MB memory area at the higher end of process address space using mmap (MAP_FIXED..). 
> 
> 2. I created a new arena using arenas.extend mallctl
> 
> 3. I am using mallocx/dallocx with MALLOCX_ARENA(arena) as documented. 
> 
> The issue is how do I connect the arena to mmaped memory chunk ? I see that new arena never gets initialized and all allocations continue to happen from arena 0x0.
> I thought thread.arena mallctl will connect the arena to mmapped chunk but it just creates a thread <-> arena mapping. 
> 
> I looked at the sources to see if there is any other mallctl to create this association but there does not seem to be any, what am I missing here ?
> 
> And older sample program I found on this mailing list, uses following mallctl which is not supported in jemalloc 3.6.
> 
> 
> snprintf(path, sizeof(path), "arena.%u.chunk.alloc", _arena);
>   ret = __svm_mallctl(path, (void*)&_chunk_alloc, &sz, (void*)&_chunk_alloc, sizeof(void *));
>   assert (ret == 0); 
> 
> snprintf(path, sizeof(path), "arena.%u.chunk.dalloc", _arena);
>   ret = __svm_mallctl(path, (void*)&_chunk_dalloc, &sz, (void*)&_chunk_dalloc, sizeof(void *));
>   assert (ret == 0); 
> 
> 
> This basically is asking jemalloc to callback user defined functions, is this functionality still available in jemalloc ? Any inputs will be helpful. Thanks. 

The features you're trying to use only exist in the dev version of jemalloc so far ("arena.<i>.chunk.alloc" and "arena.<i>.chunk.dalloc" mallctl interfaces).  Note that related control over dirty page purging still needs to be implemented (https://github.com/jemalloc/jemalloc/issues/93).

Jason