mm/vmalloc: do not keep unpurged areas in the busy tree

The busy tree can be quite big, even though the area is freed or unmapped
it still stays there until "purge" logic removes it.

1) Optimize and reduce the size of "busy" tree by removing a node from
   it right away as soon as user triggers free paths.  It is possible to
   do so, because the allocation is done using another augmented tree.

The vmalloc test driver shows the difference, for example the
"fix_size_alloc_test" is ~11% better comparing with default configuration:

sudo ./test_vmalloc.sh performance

<default>
Summary: fix_size_alloc_test loops: 1000000 avg: 993985 usec
Summary: full_fit_alloc_test loops: 1000000 avg: 973554 usec
Summary: long_busy_list_alloc_test loops: 1000000 avg: 12617652 usec
<default>

<this patch>
Summary: fix_size_alloc_test loops: 1000000 avg: 882263 usec
Summary: full_fit_alloc_test loops: 1000000 avg: 973407 usec
Summary: long_busy_list_alloc_test loops: 1000000 avg: 12593929 usec
<this patch>

2) Since the busy tree now contains allocated areas only and does not
   interfere with lazily free nodes, introduce the new function
   show_purge_info() that dumps "unpurged" areas that is propagated
   through "/proc/vmallocinfo".

3) Eliminate VM_LAZY_FREE flag.

Link: http://lkml.kernel.org/r/20190716152656.12255-2-lpf.vector@gmail.com


Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Pengfei Li <lpf.vector@gmail.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>