[RFC PATCH 0/3] fs/proc: split the inode list for procfs

[Huang Shijie]

The global s_inode_list_lock is heavily contended in procfs
on a 384-CPU, 12-NUMA-node Hygon machine running Hadoop TestDFSIO:
  #hadoop jar xxxx.jar TestDFSIO -read -nrFiles 1000 -size 100MB

The hadoop will create lot of threads during the test.
The perf shows it consuming ~90% of the lock hotspot in procfs.
The lock is hit from both directions:
   -- inode creation (~49%) :
           getdents64 ->
              proc_readfd_common ->
	         new_inode ->
		   inode_sb_list_add()

   -- inode eviction (~41%):
           process exit ->
	      release_task ->
	         proc_invalidate_siblings_dcache ->
		     evict ->
		        inode_sb_list_del()

This patch set tries to resolve this issue by:
    patch 1: "fs/drop_caches: do not scan procfs in drop_pagecache_sb()"
       This patch skips the scan for procfs in drop caches.

    patch 2: Add a new helper to detect the empty inode list    

    patch 3: split the inode list.


After this patch, the above TestDFSIO can get over 50% better performance
in exec time. And the procfs lock hotspot becomes nearly 1%.

Huang Shijie (3):
  fs/drop_caches: do not scan procfs in drop_pagecache_sb()
  fs/super: introduce a helper sb_inodes_empty()
  fs/proc: split the inode list

 fs/drop_caches.c               |  4 ++
 fs/inode.c                     | 80 ++++++++++++++++++++++------------
 fs/proc/inode.c                | 53 ++++++++++++++++++++++
 fs/proc/internal.h             |  2 +
 fs/proc/root.c                 |  6 +++
 fs/super.c                     | 45 +++++++++++++++----
 include/linux/fs/super_types.h | 22 +++++++++-
 include/linux/proc_fs.h        |  1 +
 8 files changed, 176 insertions(+), 37 deletions(-)

-- 
2.53.0