Re: [PATCH] Add LD_NUMA_REPLICATION for glibc

[Florian Weimer via Libc-alpha <libc-alpha@sourceware.org>]

* Huang Shijie via Libc-alpha:

> This patch adds LD_NUMA_REPLICATION which influences the linkage of shared libraries at run time.
>
> If LD_NUMA_REPLICATION is set for program foo like this:
> 	#LD_NUMA_REPLICATION=1 ./foo
>
> At the time ld.so mmaps the shared libraries, it will uses
> 	mmap(, c->prot | PROT_WRITE, MAP_COPY | MAP_FILE | MAP_POPULATE,)
> for them, and the mmap will trigger COW(copy on write) for the shared
> libraries at the NUMA node which the program `foo` runs. After the
> COW, the foo will have a copy of the shared library segment(mmap
> covered) which belong to the same NUMA node.
>
> So when enable LD_NUMA_REPLICATION, it will consume more memory,
> but it will reduce the remote-access in NUMA.

I think the kernel could do this in a much better way, avoiding
duplicating the pages within the same NUMA node.

The other issue is the temporary RWX mapping, which does not
interoperate well with some security hardening features.

Thanks,
Florian