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alistair23-linux/fs
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Linus Torvalds 1b6b26ae70 pipe: fix and clarify pipe write wakeup logic 
The pipe rework ends up having been extra painful, partly becaused of
actual bugs with ordering and caching of the pipe state, but also
because of subtle performance issues.

In particular, the pipe rework caused the kernel build to inexplicably
slow down.

The reason turns out to be that the GNU make jobserver (which limits the
parallelism of the build) uses a pipe to implement a "token" system: a
parallel submake will read a character from the pipe to get the job
token before starting a new job, and will write a character back to the
pipe when it is done.  The overall job limit is thus easily controlled
by just writing the appropriate number of initial token characters into
the pipe.

But to work well, that really means that the old behavior of write
wakeups being synchronous (WF_SYNC) is very important - when the pipe
writer wakes up a reader, we want the reader to actually get scheduled
immediately.  Otherwise you lose the parallelism of the build.

The pipe rework lost that synchronous wakeup on write, and we had
clearly all forgotten the reasons and rules for it.

This rewrites the pipe write wakeup logic to do the required Wsync
wakeups, but also clarifies the logic and avoids extraneous wakeups.

It also ends up addign a number of comments about what oit does and why,
so that we hopefully don't end up forgetting about this next time we
change this code.

Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-12-07 12:14:28 -08:00
..
9p 9p pull request for inclusion in 5.4 2019-09-27 15:10:34 -07:00
adfs
affs affs: fix a memory leak in affs_remount 2019-11-18 14:26:43 +01:00
afs AFS development 2019-11-30 10:57:22 -08:00
autofs Merge branch 'next.autofs' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-12-05 17:11:48 -08:00
befs
bfs
btrfs compat_ioctl: remove most of fs/compat_ioctl.c 2019-12-01 13:46:15 -08:00
cachefiles
ceph The two highlights are a set of improvements to how rbd read-only 2019-12-05 13:06:51 -08:00
cifs Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-12-06 09:06:58 -08:00
coda
configfs configfs: calculate the depth of parent item 2019-11-06 18:36:01 +01:00
cramfs cramfs: fix usage on non-MTD device 2019-11-23 21:44:49 -05:00
crypto fscrypt: add support for IV_INO_LBLK_64 policies 2019-11-06 12:34:36 -08:00
debugfs Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-12-06 09:06:58 -08:00
devpts
dlm
ecryptfs compat_ioctl: remove most of fs/compat_ioctl.c 2019-12-01 13:46:15 -08:00
efivarfs
efs
erofs erofs: remove unnecessary output in erofs_show_options() 2019-11-24 11:02:41 +08:00
exportfs exportfs_decode_fh(): negative pinned may become positive without the parent locked 2019-11-10 11:56:05 -05:00
ext2 \n 2019-11-30 11:16:07 -08:00
ext4 compat_ioctl: remove most of fs/compat_ioctl.c 2019-12-01 13:46:15 -08:00
f2fs compat_ioctl: remove most of fs/compat_ioctl.c 2019-12-01 13:46:15 -08:00
fat compat_ioctl: move drivers to compat_ptr_ioctl 2019-10-23 17:23:43 +02:00
freevxfs
fscache
fuse pipe: Fix iteration end check in fuse_dev_splice_write() 2019-12-06 13:57:04 -08:00
gfs2 GFS2 changes for this merge window: 2019-12-05 13:20:11 -08:00
hfs
hfsplus
hostfs
hpfs fs: compat_ioctl: move FITRIM emulation into file systems 2019-10-23 17:23:46 +02:00
hugetlbfs hugetlb: remove unused hstate in hugetlb_fault_mutex_hash() 2019-12-01 12:59:08 -08:00
iomap iomap: remove unneeded variable in iomap_dio_rw() 2019-11-26 09:28:47 -08:00
isofs
jbd2 This merge window saw the the following new featuers added to ext4: 2019-11-30 10:53:02 -08:00
jffs2 Revert "jffs2: Fix possible null-pointer dereferences in jffs2_add_frag_to_fragtree()" 2019-11-29 11:29:58 +01:00
jfs
kernfs Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-12-06 09:06:58 -08:00
lockd
minix
nfs NFS: Fix an RCU lock leak in nfs4_refresh_delegation_stateid() 2019-11-01 11:03:56 -04:00
nfs_common
nfsd new helper: lookup_positive_unlocked() 2019-11-15 13:49:04 -05:00
nilfs2 fs: compat_ioctl: move FITRIM emulation into file systems 2019-10-23 17:23:46 +02:00
nls
notify compat_ioctl: remove most of fs/compat_ioctl.c 2019-12-01 13:46:15 -08:00
ntfs ntfs: remove (un)?likely() from IS_ERR() conditions 2019-09-26 10:10:44 -07:00
ocfs2 Merge branch 'akpm' (patches from Andrew) 2019-12-01 20:36:41 -08:00
omfs
openpromfs
orangefs
overlayfs new helper: lookup_positive_unlocked() 2019-11-15 13:49:04 -05:00
proc fs/proc/Kconfig: fix indentation 2019-12-04 19:44:11 -08:00
pstore pstore: Make pstore_choose_compression() static 2019-10-29 09:43:03 -07:00
qnx4
qnx6
quota Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-12-06 09:06:58 -08:00
ramfs
reiserfs reiserfs: replace open-coded atomic_dec_and_mutex_lock() 2019-11-05 12:25:22 +01:00
romfs
squashfs
sysfs
sysv
tracefs tracing: Do not create tracefs files if tracefs lockdown is in effect 2019-10-12 20:49:07 -04:00
ubifs ubifs: ubifs_tnc_start_commit: Fix OOB in layout_in_gaps 2019-11-17 22:22:54 +01:00
udf
ufs
unicode
verity
xfs New code for 5.5: 2019-12-02 14:46:22 -08:00
aio.c y2038: syscall implementation cleanups 2019-12-01 14:00:59 -08:00
anon_inodes.c
attr.c
bad_inode.c
binfmt_aout.c
binfmt_elf.c fs/binfmt_elf.c: extract elf_read() function 2019-12-04 19:44:13 -08:00
binfmt_elf_fdpic.c y2038: elfcore: Use __kernel_old_timeval for process times 2019-11-15 14:38:29 +01:00
binfmt_em86.c
binfmt_flat.c
binfmt_misc.c
binfmt_script.c
block_dev.c block: don't send uevent for empty disk when not invalidating 2019-12-02 18:49:30 -07:00
buffer.c fs/buffer.c: include internal.h for missing declarations 2019-12-01 06:29:17 -08:00
char_dev.c
compat.c
compat_binfmt_elf.c y2038: elfcore: Use __kernel_old_timeval for process times 2019-11-15 14:38:29 +01:00
compat_ioctl.c New code for 5.5: 2019-12-02 14:46:22 -08:00
coredump.c
d_path.c
dax.c New code for 5.5: 2019-11-30 10:44:49 -08:00
dcache.c Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-12-06 09:06:58 -08:00
dcookies.c
direct-io.c fs/direct-io.c: keep dio_warn_stale_pagecache() when CONFIG_BLOCK=n 2019-12-01 06:29:18 -08:00
drop_caches.c
eventfd.c
eventpoll.c fs/epoll: remove unnecessary wakeups of nested epoll 2019-12-04 19:44:13 -08:00
exec.c Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-12-03 12:20:25 -08:00
fcntl.c fcntl: fix typo in RWH_WRITE_LIFE_NOT_SET r/w hint name 2019-10-25 14:28:10 -06:00
fhandle.c
file.c Revert "vfs: properly and reliably lock f_pos in fdget_pos()" 2019-11-26 11:34:06 -08:00
file_table.c
filesystems.c
fs-writeback.c cgroup,writeback: don't switch wbs immediately on dead wbs if the memcg is dead 2019-11-08 13:37:24 -07:00
fs_context.c
fs_parser.c
fs_pin.c
fs_struct.c
fs_types.c
fsopen.c
inode.c mm,thp: avoid writes to file with THP in pagecache 2019-09-24 15:54:11 -07:00
internal.h
io-wq.c io_uring: use current task creds instead of allocating a new one 2019-12-02 08:50:00 -07:00
io-wq.h io-wq: clear node->next on list deletion 2019-12-04 17:26:57 -07:00
io_uring.c io_uring: fix a typo in a comment 2019-12-05 07:59:37 -07:00
ioctl.c New code for 5.5: 2019-12-02 14:46:22 -08:00
Kconfig io-wq: small threadpool implementation for io_uring 2019-10-29 12:43:00 -06:00
Kconfig.binfmt
libfs.c fs/libfs.c: fix kernel-doc warning 2019-10-14 15:04:01 -07:00
locks.c Highlights: 2019-09-27 17:00:27 -07:00
Makefile io-wq: small threadpool implementation for io_uring 2019-10-29 12:43:00 -06:00
mbcache.c
mount.h
mpage.c
namei.c Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-12-06 09:06:58 -08:00
namespace.c fs/namespace.c: fix use-after-free of mount in mnt_warn_timestamp_expiry() 2019-10-16 23:15:09 -04:00
no-block.c
nsfs.c
open.c Revert "vfs: properly and reliably lock f_pos in fdget_pos()" 2019-11-26 11:34:06 -08:00
pipe.c pipe: fix and clarify pipe write wakeup logic 2019-12-07 12:14:28 -08:00
pnode.c
pnode.h
posix_acl.c
proc_namespace.c
read_write.c
readdir.c filldir[64]: remove WARN_ON_ONCE() for bad directory entries 2019-10-18 18:41:16 -04:00
select.c y2038: syscalls: change remaining timeval to __kernel_old_timeval 2019-11-15 14:38:29 +01:00
seq_file.c
signalfd.c
splice.c pipe: fix incorrect caching of pipe state over pipe_wait() 2019-12-06 12:40:35 -08:00
stack.c
stat.c
statfs.c vfs: Fix EOVERFLOW testing in put_compat_statfs64 2019-10-03 14:21:35 -07:00
super.c Merge branch 'work.mount3' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-10-10 08:16:44 -07:00
sync.c
timerfd.c y2038: timerfd: Use timespec64 internally 2019-11-15 14:38:30 +01:00
userfaultfd.c Merge branch 'akpm' (patches from Andrew) 2019-12-01 20:36:41 -08:00
utimes.c y2038: syscalls: change remaining timeval to __kernel_old_timeval 2019-11-15 14:38:29 +01:00
xattr.c