$ sudo /usr/share/bcc/tools/memleak
# (...)
# (much spam while I launched 100 instances of glxgears, then killed them)
# (...)
[22:46:15] Top 10 stacks with outstanding allocations:
	188416 bytes in 46 allocations from stack
		__alloc_pages_nodemask+0x2b3 [kernel]
		__alloc_pages_nodemask+0x2b3 [kernel]
		pte_alloc_one+0x14 [kernel]
		__pte_alloc+0x18 [kernel]
		__handle_mm_fault+0x12fb [kernel]
		handle_mm_fault+0xce [kernel]
		__do_page_fault+0x244 [kernel]
		do_page_fault+0x33 [kernel]
		page_fault+0x1e [kernel]
	196608 bytes in 15 allocations from stack
		__alloc_pages_nodemask+0x2b3 [kernel]
		__alloc_pages_nodemask+0x2b3 [kernel]
		new_slab+0x343 [kernel]
		___slab_alloc+0x44c [kernel]
		__slab_alloc.isra.0+0x52 [kernel]
		__kmalloc_node_track_caller+0x1da [kernel]
		__kmalloc_reserve.isra.0+0x2d [kernel]
		__alloc_skb+0x87 [kernel]
		alloc_skb_with_frags+0x4d [kernel]
		sock_alloc_send_pskb+0x1ef [kernel]
		unix_stream_sendmsg+0x270 [kernel]
		sock_sendmsg+0x4f [kernel]
		sock_write_iter+0x8f [kernel]
		do_iter_readv_writev+0x166 [kernel]
		do_iter_write+0x7d [kernel]
		vfs_writev+0xbd [kernel]
		do_writev+0x73 [kernel]
		do_syscall_64+0x5f [kernel]
		entry_SYSCALL_64_after_hwframe+0x44 [kernel]
	196608 bytes in 6 allocations from stack
		__alloc_pages_nodemask+0x2b3 [kernel]
		__alloc_pages_nodemask+0x2b3 [kernel]
		new_slab+0x343 [kernel]
		___slab_alloc+0x44c [kernel]
		__slab_alloc.isra.0+0x52 [kernel]
		kmem_cache_alloc+0x180 [kernel]
		ext4_alloc_inode+0x18 [kernel]
		alloc_inode+0x1d [kernel]
		iget_locked+0xd3 [kernel]
		__ext4_iget+0x12d [kernel]
		ext4_lookup+0xd4 [kernel]
		__lookup_slow+0x95 [kernel]
		lookup_slow+0x36 [kernel]
		walk_component+0x1e5 [kernel]
		path_lookupat.isra.0+0x76 [kernel]
		filename_lookup+0xc2 [kernel]
		vfs_statx+0x8c [kernel]
		__se_sys_newlstat+0x4c [kernel]
		do_syscall_64+0x5f [kernel]
		entry_SYSCALL_64_after_hwframe+0x44 [kernel]
	376832 bytes in 92 allocations from stack
		__alloc_pages_nodemask+0x2b3 [kernel]
		__alloc_pages_nodemask+0x2b3 [kernel]
		alloc_pages_vma+0x7d [kernel]
		wp_page_copy+0xbf [kernel]
		do_wp_page+0x95 [kernel]
		__handle_mm_fault+0xc29 [kernel]
		handle_mm_fault+0xce [kernel]
		__do_page_fault+0x244 [kernel]
		do_page_fault+0x33 [kernel]
		page_fault+0x1e [kernel]
	385024 bytes in 94 allocations from stack
		__alloc_pages_nodemask+0x2b3 [kernel]
		__alloc_pages_nodemask+0x2b3 [kernel]
		alloc_pages_vma+0x7d [kernel]
		shmem_alloc_page+0x54 [kernel]
		shmem_alloc_and_acct_page+0x7c [kernel]
		shmem_getpage_gfp.isra.0+0x16e [kernel]
		shmem_fault+0xa1 [kernel]
		__do_fault+0x38 [kernel]
		__handle_mm_fault+0xd47 [kernel]
		handle_mm_fault+0xce [kernel]
		__do_page_fault+0x244 [kernel]
		do_page_fault+0x33 [kernel]
		page_fault+0x1e [kernel]
	909312 bytes in 222 allocations from stack
		__alloc_pages_nodemask+0x2b3 [kernel]
		__alloc_pages_nodemask+0x2b3 [kernel]
		pagecache_get_page+0xdb [kernel]
		__getblk_gfp+0xe3 [kernel]
		__breadahead+0x2b [kernel]
		__ext4_get_inode_loc+0x34a [kernel]
		__ext4_iget+0x15e [kernel]
		ext4_lookup+0xd4 [kernel]
		__lookup_slow+0x95 [kernel]
		lookup_slow+0x36 [kernel]
		walk_component+0x1e5 [kernel]
		path_lookupat.isra.0+0x76 [kernel]
		filename_lookup+0xc2 [kernel]
		vfs_statx+0x8c [kernel]
		__se_sys_newlstat+0x4c [kernel]
		do_syscall_64+0x5f [kernel]
		entry_SYSCALL_64_after_hwframe+0x44 [kernel]
	1032192 bytes in 126 allocations from stack
		__kmalloc_node_track_caller+0x187 [kernel]
		__kmalloc_node_track_caller+0x187 [kernel]
		__kmalloc_reserve.isra.0+0x2d [kernel]
		__alloc_skb+0x87 [kernel]
		__netdev_alloc_skb+0x3c [kernel]
		rt2x00queue_alloc_rxskb+0x49 [kernel]
		rt2x00lib_rxdone+0x75 [kernel]
		rt2x00usb_work_rxdone+0x74 [kernel]
		process_one_work+0x1d1 [kernel]
		worker_thread+0x4a [kernel]
		kthread+0xfb [kernel]
		ret_from_fork+0x22 [kernel]
	2838528 bytes in 693 allocations from stack
		__alloc_pages_nodemask+0x2b3 [kernel]
		__alloc_pages_nodemask+0x2b3 [kernel]
		__do_page_cache_readahead+0xa7 [kernel]
		ondemand_readahead+0x198 [kernel]
		filemap_fault+0x266 [kernel]
		ext4_filemap_fault+0x2d [kernel]
		__do_fault+0x38 [kernel]
		__handle_mm_fault+0xde9 [kernel]
		handle_mm_fault+0xce [kernel]
		__do_page_fault+0x244 [kernel]
		do_page_fault+0x33 [kernel]
		page_fault+0x1e [kernel]
	8175616 bytes in 1996 allocations from stack
		__alloc_pages_nodemask+0x2b3 [kernel]
		__alloc_pages_nodemask+0x2b3 [kernel]
		__do_page_cache_readahead+0xa7 [kernel]
		filemap_fault+0x388 [kernel]
		ext4_filemap_fault+0x2d [kernel]
		__do_fault+0x38 [kernel]
		__handle_mm_fault+0xde9 [kernel]
		handle_mm_fault+0xce [kernel]
		__do_page_fault+0x244 [kernel]
		do_page_fault+0x33 [kernel]
		page_fault+0x1e [kernel]
	27226112 bytes in 6647 allocations from stack
		__alloc_pages_nodemask+0x2b3 [kernel]
		__alloc_pages_nodemask+0x2b3 [kernel]
		alloc_pages_vma+0x7d [kernel]
		__handle_mm_fault+0xe61 [kernel]
		handle_mm_fault+0xce [kernel]
		__do_page_fault+0x244 [kernel]
		do_page_fault+0x33 [kernel]
		page_fault+0x1e [kernel]

$ sudo sh -c 'sync && free && echo 3 > /proc/sys/vm/drop_caches && sync && free'
              total        used        free      shared  buff/cache   available
Mem:        6046652      368412     5223572        3392      454668     5436692
Swap:             0           0           0
              total        used        free      shared  buff/cache   available
Mem:        6046652      367680     5485580        3392      193392     5443648
Swap:             0           0           0
# only about 7 megabytes of RAM were missing after killing the glxgears