[RFC] Name memory regions allocated with mmap (prctl PR_SET_VMA_ANON_NAME)

[alban]

Suggestion

Every time cilium/ebpf uses mmap(MAP_ANONYMOUS), it should give a name to the memory region indicating its purpose (i.e. ring buffer for a specific ebpf map).

        share = mmap(NULL, SIZE, PROT_READ | PROT_WRITE,
                     MAP_SHARED | MAP_ANONYMOUS, -1, 0);
        rv = prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME,
                   share, SIZE, "ebpf map foo");

Use case

Investigate why my application is using too much memory by looking at /proc/pid/maps.

Applications can allocate memory with mmap(MAP_ANONYMOUS) from various libraries. When investigating memory issues, I look at /proc/pid/maps. When the memory regions are anonymous, it is difficult to understand where the allocations are coming from. If cilium/ebpf was labelling the perf ring buffers and other mmap memory region, it would help me understand if I gave too much memory to my ebpf maps, or if the problem is in another library than cilium/ebpf.

This requires:

• Linux 5.17 for torvalds/linux@9a10064
• CONFIG_ANON_VMA_NAME

xref inspektor-gadget/inspektor-gadget#3541 (comment)

cc @burak-ok

[ti-mo]

Interesting, this could help with the new Map.Memory() API as well. Would be nice to see the names show up in pmap.

[ti-mo]

Interesting, this could help with the new Map.Memory() API as well. Would be nice to see the names show up in pmap.

Unfortunately, this doesn't seem to work for mmapable bpf maps. Since https://lwn.net/Articles/913935, naming is supported for MAP_SHARED | MAP_ANON, but BPF maps already show up as anon_inode:bpf-map in /proc/self/maps, which likely falls outside of this category.