use the glibc malloc hooks to replace the libc allocator on Linux

[thestinger]

On Linux, we can replace the glibc allocator via the malloc hooks. This will reduce external fragmentation by moving allocation used by C libraries to jemalloc.

[huonw]

Does this work with alternative libc's like musl, etc.?

[thestinger]

@huonw: They'll need to be separate targets since the ABI differs and not all of the Linux-specific functions are provided. It doesn't seem that musl provides these specific variables, but I think it's intended to cover the useful part of the glibc ABI eventually so it might in the future.

[ebfe]

FWIW, __malloc_hook etc. have been marked deprecated in glibc for quite some time now.

[thestinger]

The weak symbols are only usable in a dynamically linked library. When using static linking, you still need to use the hooks, whether or not they're marked as deprecated.

https://sourceware.org/ml/libc-alpha/2011-07/msg00136.html

Now that Drepper isn't in charge, I doubt that these will be removed with no replacement available.

[thestinger]

I reported a bug: https://sourceware.org/bugzilla/show_bug.cgi?id=16939

Regardless, since they're still around I think it's okay to use them. If these globals go away, we can just stop setting them.

[thestinger]

Not really a viable option because it doesn't cover the whole API.