mm/mmap: move vma operations to mm_struct out of the critical section of file mapping lock

UnixBench/Execl represents a class of workload where bash scripts are
spawned frequently to do some short jobs.  When running multiple parallel
tasks, hot osq_lock is observed from do_mmap and exit_mmap.  Both of them
come from load_elf_binary through the call chain
"execl->do_execveat_common->bprm_execve->load_elf_binary".

In do_mmap,it will call mmap_region to create vma node, initialize it and
insert it to vma maintain structure in mm_struct and i_mmap tree of the
mapping file, then increase map_count to record the number of vma nodes
used.  The hot osq_lock is to protect operations on file's i_mmap tree. 
For the mm_struct member change like vma insertion and map_count update,
they do not affect i_mmap tree.  Move those operations out of the lock's
critical section, to reduce hold time on the lock.

With this change, on Intel Sapphire Rapids 112C/224T platform, based on
v6.0-rc6, the 160 parallel score improves by 12%.  The patch has no
obvious performance gain on v6.5-rc1 due to regression of this benchmark
from this commit f1a7941243c102a44e8847e3b94ff4ff3ec56f25 (mm: convert
mm's rss stats into percpu_counter).  Related discussion and conclusion
can be referred at the mail thread initiated by 0day as below: Link:
https://lore.kernel.org/linux-mm/[email protected]/

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Yu Ma <[email protected]>
Reviewed-by: Tim Chen <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Kirill A . Shutemov <[email protected]>
Cc: Liam R. Howlett <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Zhu, Lipeng <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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