Re: [PATCH] Add LD_NUMA_REPLICATION for glibc

[Huang Shijie <shijie@os.amperecomputing.com>]

On Fri, Sep 03, 2021 at 08:28:57AM +0200, Florian Weimer wrote:
> * 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.
I think maybe only the per-NUMA-node page cache can avoid it..

> 
> The other issue is the temporary RWX mapping, which does not
> interoperate well with some security hardening features.
> 
Thanks for the feedback.
I CC more people who may  have interesting about this.


Thanks
Huang Shijie