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NeilBrown f1ee616214 VFS: don't keep disconnected dentries on d_anon 
The original purpose of the per-superblock d_anon list was to
keep disconnected dentries in the cache between consecutive
requests to the NFS server.  Dentries can be disconnected if
a client holds a file open and repeatedly performs IO on it,
and if the server drops the dentry, whether due to memory
pressure, server restart, or "echo 3 > /proc/sys/vm/drop_caches".

This purpose was thwarted by commit 75a6f82a0d ("freeing unlinked
file indefinitely delayed") which caused disconnected dentries
to be freed as soon as their refcount reached zero.

This means that, when a dentry being used by nfsd gets disconnected, a
new one needs to be allocated for every request (unless requests
overlap).  As the dentry has no name, no parent, and no children,
there is little of value to cache.  As small memory allocations are
typically fast (from per-cpu free lists) this likely has little cost.

This means that the original purpose of s_anon is no longer relevant:
there is no longer any need to keep disconnected dentries on a list so
they appear to be hashed.

However, s_anon now has a new use.  When you mount an NFS filesystem,
the dentry stored in s_root is just a placebo.  The "real" root dentry
is allocated using d_obtain_root() and so it kept on the s_anon list.
I don't know the reason for this, but suspect it related to NFSv4
where a mount of "server:/some/path" require NFS to look up the root
filehandle on the server, then walk down "/some" and "/path" to get
the filehandle to mount.

Whatever the reason, NFS depends on the s_anon list and on
shrink_dcache_for_umount() pruning all dentries on this list.  So we
cannot simply remove s_anon.

We could just leave the code unchanged, but apart from that being
potentially confusing, the (unfair) bit-spin-lock which protects
s_anon can become a bottle neck when lots of disconnected dentries are
being created.

So this patch renames s_anon to s_roots, and stops storing
disconnected dentries on the list.  Only dentries obtained with
d_obtain_root() are now stored on this list.  There are many fewer of
these (only NFS and NILFS2 use the call, and only during filesystem
mount) so contention on the bit-lock will not be a problem.

Possibly an alternate solution should be found for NFS and NILFS2, but
that would require understanding their needs first.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
 		2017-12-25 20:22:07 -05:00
..
9p Merge branch '9p-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-11-22 20:17:54 -10:00
adfs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
affs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
afs afs: remove redundant assignment of dvnode to itself 2017-11-24 13:55:46 +00:00
autofs4 autofs: don't fail mount for transient error 2017-11-17 16:10:02 -08:00
befs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
bfs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
btrfs AFS development 2017-11-16 11:41:22 -08:00
cachefiles mm: remove __GFP_COLD 2017-11-15 18:21:06 -08:00
ceph We have a set of file locking improvements from Zheng, rbd rw/ro 2017-11-21 05:38:32 -10:00
cifs cifs: use find_get_pages_range_tag() 2017-11-15 18:21:04 -08:00
coda Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-11-17 12:54:01 -08:00
configfs configfs: make ci_type field, some pointers and function arguments const 2017-10-19 16:15:16 +02:00
cramfs Merge branch 'work.cramfs' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-11-17 13:20:41 -08:00
crypto fscrypt: lots of cleanups, mostly courtesy by Eric Biggers 2017-11-14 11:35:15 -08:00
debugfs debugfs: Remove redundant license text 2017-11-07 20:25:03 +01:00
devpts pty: Repair TIOCGPTPEER 2017-08-24 13:23:03 -07:00
dlm A couple of configfs cleanups: 2017-11-14 14:44:04 -08:00
ecryptfs * Miscellaneous code cleanups and refactoring 2017-11-17 14:16:21 -08:00
efivarfs VFS: Kill off s_options and helpers 2017-07-11 06:09:21 -04:00
efs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
exofs Merge branch 'for-4.14/block' of git://git.kernel.dk/linux-block 2017-09-07 11:59:42 -07:00
exportfs
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ext2 libnvdimm for 4.15 2017-11-17 09:51:57 -08:00
ext4 Merge branch 'misc.compat' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-11-17 11:54:55 -08:00
f2fs f2fs-for-4.15-rc1 2017-11-16 12:10:21 -08:00
fat fat: remove redundant assignment of 0 to slots 2017-11-17 16:10:03 -08:00
freevxfs
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fscache AFS development 2017-11-16 11:41:22 -08:00
fuse Merge branch 'akpm' (patches from Andrew) 2017-11-15 19:42:40 -08:00
gfs2 mm, pagevec: remove cold parameter for pagevecs 2017-11-15 18:21:06 -08:00
hfs hfs/hfsplus: clean up unused variables in bnode.c 2017-11-17 16:10:03 -08:00
hfsplus hfs/hfsplus: clean up unused variables in bnode.c 2017-11-17 16:10:03 -08:00
hostfs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
hpfs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
hugetlbfs mm, pagevec: remove cold parameter for pagevecs 2017-11-15 18:21:06 -08:00
isofs Merge branch 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs 2017-11-14 14:13:11 -08:00
jbd2 libnvdimm for 4.15 2017-11-17 09:51:57 -08:00
jffs2 License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
jfs A couple small fixes for jfs 2017-11-14 13:53:18 -08:00
kernfs Merge branch 'for-4.14/block' of git://git.kernel.dk/linux-block 2017-09-07 11:59:42 -07:00
lockd Lots of good bugfixes, including: 2017-11-18 11:22:04 -08:00
minix License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ncpfs Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-11-13 17:56:58 -08:00
nfs NFS client updates for Linux 4.15 2017-11-17 14:18:00 -08:00
nfs_common nfs_common: convert int to bool 2017-09-26 09:25:38 -04:00
nfsd Lots of good bugfixes, including: 2017-11-18 11:22:04 -08:00
nilfs2 nilfs2: remove inode->i_version initialization 2017-11-17 16:10:03 -08:00
nls License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
notify Merge branch 'for-linus' of ssh://gitolite.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2017-11-15 10:14:11 -08:00
ntfs Merge branch 'for-4.15/block' of git://git.kernel.dk/linux-block 2017-11-14 15:32:19 -08:00
ocfs2 treewide: setup_timer() -> timer_setup() 2017-11-21 15:57:07 -08:00
omfs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
openpromfs
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orangefs 3 Cleanups: remove initialization of i_version - Jeff Layton 2017-11-21 05:40:48 -10:00
overlayfs Merge branch 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs 2017-11-17 13:36:59 -08:00
proc Merge branch 'work.whack-a-mole' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-11-22 20:20:02 -10:00
pstore treewide: Switch DEFINE_TIMER callbacks to struct timer_list * 2017-11-21 15:57:05 -08:00
qnx4 License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
qnx6 License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
quota Merge branch 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs 2017-11-14 14:13:11 -08:00
ramfs mm: make pagevec_lookup() update index 2017-09-06 17:27:26 -07:00
reiserfs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
romfs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
squashfs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
sysfs
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sysv License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
tracefs VFS: Don't use save/replace_mount_options if not using generic_show_options 2017-07-06 03:31:46 -04:00
ubifs fscrypt: lots of cleanups, mostly courtesy by Eric Biggers 2017-11-14 11:35:15 -08:00
udf Merge branch 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs 2017-11-14 14:13:11 -08:00
ufs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
xfs Changes since last update: 2017-11-22 20:42:42 -10:00
Kconfig fs/Kconfig: kill CONFIG_PERCPU_RWSEM some more 2017-07-12 16:26:00 -07:00
Kconfig.binfmt ARM: enable elf_fdpic on systems with an MMU 2017-09-10 19:31:46 -04:00
Makefile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
aio.c Merge branch 'misc.compat' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-11-17 11:54:55 -08:00
anon_inodes.c
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attr.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
bad_inode.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
binfmt_aout.c fs: fix kernel_read prototype 2017-09-04 19:05:15 -04:00
binfmt_elf.c Merge branch 'for-linus' of git://git.armlinux.org.uk/~rmk/linux-arm 2017-11-16 12:50:35 -08:00
binfmt_elf_fdpic.c Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-11-17 12:54:01 -08:00
binfmt_em86.c
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binfmt_flat.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
binfmt_misc.c fs/binfmt_misc.c: node could be NULL when evicting inode 2017-10-13 16:18:33 -07:00
binfmt_script.c exec: load_script: kill the onstack interp[BINPRM_BUF_SIZE] array 2017-10-03 17:54:25 -07:00
block_dev.c Merge branch 'for-4.15/block' of git://git.kernel.dk/linux-block 2017-11-14 15:32:19 -08:00
buffer.c mm, pagevec: remove cold parameter for pagevecs 2017-11-15 18:21:06 -08:00
char_dev.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
compat.c
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compat_binfmt_elf.c
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compat_ioctl.c Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-11-17 12:54:01 -08:00
coredump.c Merge branch 'misc.compat' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-11-17 11:54:55 -08:00
dax.c libnvdimm for 4.15 2017-11-17 09:51:57 -08:00
dcache.c VFS: don't keep disconnected dentries on d_anon 2017-12-25 20:22:07 -05:00
dcookies.c
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direct-io.c Merge branch 'for-4.15/block' of git://git.kernel.dk/linux-block 2017-11-14 15:32:19 -08:00
drop_caches.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
eventfd.c There has been a fair amount of activity in the docs tree this time 2017-07-03 21:13:25 -07:00
eventpoll.c Merge branch 'akpm' (patches from Andrew) 2017-11-17 16:56:17 -08:00
exec.c locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE() 2017-10-25 11:01:08 +02:00
fcntl.c fcntl: don't cap l_start and l_end values for F_GETLK64 in compat syscall 2017-11-15 08:08:36 -05:00
fhandle.c Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-11-17 12:54:01 -08:00
file.c fs/file.c: trim includes 2017-12-05 09:41:03 -05:00
file_table.c vfs: remove unused hardirq.h 2017-12-07 14:23:30 -05:00
filesystems.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
fs-writeback.c writeback: merge try_to_writeback_inodes_sb_nr() into caller 2017-10-10 08:14:37 -06:00
fs_pin.c Merge branch 'linus' into locking/core, to resolve conflicts 2017-11-07 10:32:44 +01:00
fs_struct.c
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inode.c locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE() 2017-10-25 11:01:08 +02:00
internal.h fs: expose do_unlinkat for built-in callers 2017-11-10 08:48:46 -05:00
ioctl.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
iomap.c Merge branch 'work.iov_iter' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-11-17 12:08:18 -08:00
libfs.c fs: convert __generic_file_fsync to use errseq_t based reporting 2017-07-06 07:02:29 -04:00
locks.c locks: restore a warn for leaked locks on close 2017-07-21 13:57:31 -04:00
mbcache.c ext4: xattr inode deduplication 2017-06-22 11:44:55 -04:00
mount.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mpage.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
namei.c Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-11-17 12:54:01 -08:00
namespace.c vfs: fix mounting a filesystem with i_version 2017-11-08 15:16:36 -05:00
no-block.c
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nsfs.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
open.c ovl: don't allow writing ioctl on lower layer 2017-09-05 12:53:12 +02:00
pipe.c pipe: add proc_dopipe_max_size() to safely assign pipe_max_size 2017-11-17 16:10:03 -08:00
pnode.c
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pnode.h
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posix_acl.c
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proc_namespace.c Merge branch 'linus' into locking/core, to resolve conflicts 2017-11-07 10:32:44 +01:00
read_write.c Merge branch 'work.iov_iter' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-11-17 12:08:18 -08:00
readdir.c Merge branch 'linus' into locking/core, to resolve conflicts 2017-11-07 10:32:44 +01:00
select.c Merge branch 'misc.compat' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-11-17 11:54:55 -08:00
seq_file.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
signalfd.c Merge branch 'misc.compat' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-11-17 11:54:55 -08:00
splice.c locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE() 2017-10-25 11:01:08 +02:00
stack.c
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stat.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
statfs.c Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-11-17 12:54:01 -08:00
super.c VFS: don't keep disconnected dentries on d_anon 2017-12-25 20:22:07 -05:00
sync.c Merge branch 'for-4.15/block' of git://git.kernel.dk/linux-block 2017-11-14 15:32:19 -08:00
timerfd.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
userfaultfd.c userfaultfd: use mmgrab instead of open-coded increment of mm_count 2017-11-15 18:21:05 -08:00
utimes.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
xattr.c lsm: fix smack_inode_removexattr and xattr_getsecurity memleak 2017-10-04 18:03:15 +11:00