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alistair23-linux/fs
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Andi Kleen ef3d0fd27e vfs: do (nearly) lockless generic_file_llseek 
The i_mutex lock use of generic _file_llseek hurts.  Independent processes
accessing the same file synchronize over a single lock, even though
they have no need for synchronization at all.

Under high utilization this can cause llseek to scale very poorly on larger
systems.

This patch does some rethinking of the llseek locking model:

First the 64bit f_pos is not necessarily atomic without locks
on 32bit systems. This can already cause races with read() today.
This was discussed on linux-kernel in the past and deemed acceptable.
The patch does not change that.

Let's look at the different seek variants:

SEEK_SET: Doesn't really need any locking.
If there's a race one writer wins, the other loses.

For 32bit the non atomic update races against read()
stay the same. Without a lock they can also happen
against write() now.  The read() race was deemed
acceptable in past discussions, and I think if it's
ok for read it's ok for write too.

=> Don't need a lock.

SEEK_END: This behaves like SEEK_SET plus it reads
the maximum size too. Reading the maximum size would have the
32bit atomic problem. But luckily we already have a way to read
the maximum size without locking (i_size_read), so we
can just use that instead.

Without i_mutex there is no synchronization with write() anymore,
however since the write() update is atomic on 64bit it just behaves
like another racy SEEK_SET.  On non atomic 32bit it's the same
as SEEK_SET.

=> Don't need a lock, but need to use i_size_read()

SEEK_CUR: This has a read-modify-write race window
on the same file. One could argue that any application
doing unsynchronized seeks on the same file is already broken.
But for the sake of not adding a regression here I'm
using the file->f_lock to synchronize this. Using this
lock is much better than the inode mutex because it doesn't
synchronize between processes.

=> So still need a lock, but can use a f_lock.

This patch implements this new scheme in generic_file_llseek.
I dropped generic_file_llseek_unlocked and changed all callers.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
2011-10-28 14:58:58 +02:00
..
9p fs/9p: Use protocol-defined value for lock/getlock 'type' field. 2011-09-06 08:17:16 -05:00
adfs Fix common misspellings 2011-03-31 11:26:23 -03:00
affs fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers 2011-07-20 20:47:59 -04:00
afs AFS: Fix silly characters in a comment 2011-07-20 20:48:03 -04:00
autofs4 autofs4: fix debug printk warning uncovered by cleanup 2011-08-08 12:02:43 -07:00
befs befs: Validate length of long symbolic links. 2011-08-17 13:31:24 -07:00
bfs bfs: remove unnecessary dentry_unhash on dir rename 2011-05-28 01:02:50 -04:00
btrfs vfs: do (nearly) lockless generic_file_llseek 2011-10-28 14:58:58 +02:00
cachefiles kill useless checks for sb->s_op == NULL 2011-07-20 01:44:21 -04:00
ceph Merge branch 'for-linus' of git://ceph.newdream.net/git/ceph-client 2011-09-09 15:48:34 -07:00
cifs vfs: do (nearly) lockless generic_file_llseek 2011-10-28 14:58:58 +02:00
coda fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers 2011-07-20 20:47:59 -04:00
configfs configfs: remove unnecessary dentry_unhash on rmdir, dir rename 2011-05-28 01:02:54 -04:00
cramfs cramfs: get_cramfs_inode() returns ERR_PTR() on failure 2011-07-17 23:22:02 -04:00
debugfs debugfs: move to new strtobool 2011-05-19 16:55:28 +09:30
devpts fs/devpts/inode.c: correctly check d_alloc_name() return code in devpts_pty_new() 2011-03-22 17:44:17 -07:00
dlm Merge branch 'for-3.1' of git://linux-nfs.org/~bfields/linux 2011-07-25 22:49:19 -07:00
ecryptfs Ecryptfs: Add mount option to check uid of device being mounted = expect uid 2011-08-09 23:29:01 -05:00
efs make d_splice_alias(ERR_PTR(err), dentry) = ERR_PTR(err) 2011-07-20 01:44:26 -04:00
exofs Merge branch 'for-linus' of git://git.open-osd.org/linux-open-osd 2011-08-06 22:56:03 -07:00
exportfs vfs: Add open by file handle support 2011-03-15 02:21:44 -04:00
ext2 Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6 2011-08-01 13:48:31 -10:00
ext3 block: separate priority boosting from REQ_META 2011-08-23 14:50:29 +02:00
ext4 Merge branch 'for-linus' of git://git.kernel.dk/linux-block 2011-09-21 13:20:21 -07:00
fat Merge git://git.kernel.org/pub/scm/linux/kernel/git/hirofumi/fatfs-2.6 2011-08-18 14:16:13 -07:00
freevxfs treewide: fix a few typos in comments 2011-05-10 10:16:21 +02:00
fscache FS-Cache: Fix __fscache_uncache_all_inode_pages()'s outer loop 2011-07-21 10:59:16 -07:00
fuse fuse: fix memory leak 2011-09-12 11:47:10 -07:00
gfs2 vfs: do (nearly) lockless generic_file_llseek 2011-10-28 14:58:58 +02:00
hfs fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers 2011-07-20 20:47:59 -04:00
hfsplus hfsplus: fix filesystem size checks 2011-09-15 09:03:17 -07:00
hostfs fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers 2011-07-20 20:47:59 -04:00
hpfs fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers 2011-07-20 20:47:59 -04:00
hppfs hppfs: missing include 2011-07-27 22:21:58 -04:00
hugetlbfs lockdep: Add helper function for dir vs file i_mutex annotation 2011-08-25 10:50:18 -07:00
isofs isofs: Remove global fs lock 2011-07-22 19:42:12 -04:00
jbd jbd: Use WRITE_SYNC in journal checkpoint. 2011-06-28 00:06:41 +02:00
jbd2 jbd2: remove jbd2_dev_to_name() from jbd2 tracepoints 2011-07-10 22:05:08 -04:00
jffs2 switch posix_acl_equiv_mode() to umode_t * 2011-08-01 02:10:06 -04:00
jfs Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/shaggy/jfs-2.6 2011-08-15 08:40:24 -07:00
lockd Merge branch 'nfs-for-3.1' of git://git.linux-nfs.org/projects/trondmy/linux-nfs 2011-07-27 13:23:02 -07:00
logfs fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers 2011-07-20 20:47:59 -04:00
minix minix_getattr(): don't bother with ->d_parent 2011-07-20 20:47:53 -04:00
ncpfs fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers 2011-07-20 20:47:59 -04:00
nfs vfs: do (nearly) lockless generic_file_llseek 2011-10-28 14:58:58 +02:00
nfs_common Fix common misspellings 2011-03-31 11:26:23 -03:00
nfsd Merge branch 'for-3.1' of git://linux-nfs.org/~bfields/linux 2011-07-25 22:49:19 -07:00
nilfs2 fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers 2011-07-20 20:47:59 -04:00
nls
notify atomic: use <linux/atomic.h> 2011-07-26 16:49:47 -07:00
ntfs atomic: use <linux/atomic.h> 2011-07-26 16:49:47 -07:00
ocfs2 switch posix_acl_equiv_mode() to umode_t * 2011-08-01 02:10:06 -04:00
omfs omfs: fix (mode & S_IFDIR) abuse 2011-07-26 13:05:28 -04:00
openpromfs fs: icache RCU free inodes 2011-01-07 17:50:26 +11:00
partitions Merge branch 'for-linus' into for-3.1/core 2011-07-01 16:17:13 +02:00
proc teach /proc/$pid/numa_maps about transparent hugepages 2011-09-21 13:15:44 -07:00
pstore pstore: Allow the user to explicitly choose a backend 2011-07-22 16:14:39 -07:00
qnx4 block: remove per-queue plugging 2011-03-10 08:52:07 +01:00
quota VFS: Fix the remaining automounter semantics regressions 2011-09-26 19:16:46 -07:00
ramfs ramfs: fix memleak on no-mmu arch 2011-04-14 16:06:56 -07:00
reiserfs switch posix_acl_equiv_mode() to umode_t * 2011-08-01 02:10:06 -04:00
romfs romfs: fix romfs_get_unmapped_area() argument check 2011-06-27 18:00:12 -07:00
squashfs Merge git://git.kernel.org/pub/scm/linux/kernel/git/pkl/squashfs-linus 2011-07-25 22:50:35 -07:00
sysfs ->permission() sanitizing: don't pass flags to ->permission() 2011-07-20 01:43:24 -04:00
sysv sysv: remove unnecessary dentry_unhash from rmdir, dir rename 2011-05-28 01:02:50 -04:00
ubifs UBIFS: not build debug messages with CONFIG_UBIFS_FS_DEBUG disabled 2011-08-19 18:58:58 +03:00
udf switch udf_ioctl() to inode_permission() 2011-07-20 01:43:07 -04:00
ufs make d_splice_alias(ERR_PTR(err), dentry) = ERR_PTR(err) 2011-07-20 01:44:26 -04:00
xfs xfs: revert to using a kthread for AIL pushing 2011-10-11 11:02:49 -05:00
aio.c Merge branch 'for-2.6.39/core' of git://git.kernel.dk/linux-2.6-block 2011-03-24 10:16:26 -07:00
anon_inodes.c vfs: dont chain pipe/anon/socket on superblock s_inodes list 2011-07-26 12:57:09 -04:00
attr.c fs: move inode_dio_wait calls into ->setattr 2011-07-20 20:47:47 -04:00
bad_inode.c fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers 2011-07-20 20:47:59 -04:00
binfmt_aout.c
binfmt_elf.c consolidate BINPRM_FLAGS_ENFORCE_NONDUMP handling 2011-07-20 01:43:10 -04:00
binfmt_elf_fdpic.c consolidate BINPRM_FLAGS_ENFORCE_NONDUMP handling 2011-07-20 01:43:10 -04:00
binfmt_em86.c
binfmt_flat.c CRED: Fix load_flat_shared_library() to initialise bprm correctly 2011-05-03 10:10:51 +10:00
binfmt_misc.c consolidate BINPRM_FLAGS_ENFORCE_NONDUMP handling 2011-07-20 01:43:10 -04:00
binfmt_script.c
binfmt_som.c
bio-integrity.c block: Require subsystems to explicitly allocate bio_set integrity mempool 2011-03-17 11:11:05 +01:00
bio.c block: improve the bio_add_page() and bio_add_pc_page() descriptions 2011-05-28 14:44:46 +02:00
block_dev.c Avoid dereferencing a 'request_queue' after last close. 2011-09-10 17:20:21 +10:00
buffer.c cleanup: vfs: small comment fix for block_invalidatepage 2011-10-28 13:55:08 +02:00
char_dev.c Merge branch 'for-2.6.38/core' of git://git.kernel.dk/linux-2.6-block 2011-01-13 10:45:01 -08:00
compat.c compat: sync compat_stats with statfs. 2011-10-28 14:58:53 +02:00
compat_binfmt_elf.c
compat_ioctl.c compat_ioctl: add compat handler for PPPIOCGL2TPSTATS 2011-08-07 22:24:41 -07:00
dcache.c vfs: renumber DCACHE_xyz flags, remove some stale ones 2011-08-06 22:52:40 -07:00
dcookies.c oprofile, dcookies: Fix possible circular locking dependency 2011-05-31 16:33:35 +02:00
direct-io.c direct-io: merge direct_io_walker into __blockdev_direct_IO 2011-10-28 14:58:58 +02:00
drop_caches.c vmscan: change shrinker API by passing shrink_control struct 2011-05-25 08:39:26 -07:00
eventfd.c Docbook: add fs/eventfd.c and fix typos in it 2011-02-21 15:07:04 -08:00
eventpoll.c atomic: use <linux/atomic.h> 2011-07-26 16:49:47 -07:00
exec.c move RLIMIT_NPROC check from set_user() to do_execve_common() 2011-08-11 11:24:42 -07:00
fcntl.c userns: rename is_owner_or_cap to inode_owner_or_capable 2011-03-23 19:47:13 -07:00
fhandle.c fs/fhandle.c: add <linux/personality.h> for ia64 2011-04-14 16:06:56 -07:00
fifo.c Filesystem: fifo: Fixed coding style issue. 2011-03-21 00:16:09 -04:00
file.c vfs: avoid large kmalloc()s for the fdtable 2011-04-28 11:28:20 -07:00
file_table.c atomic: use <linux/atomic.h> 2011-07-26 16:49:47 -07:00
filesystems.c fs: synchronize_rcu when unregister_filesystem success not failure 2011-04-17 10:42:01 -07:00
fs-writeback.c don't busy retry the inode on failed grab_super_passive() 2011-07-31 22:52:08 +08:00
fs_struct.c sanitize vfsmount refcounting changes 2011-01-16 13:47:07 -05:00
generic_acl.c switch posix_acl_equiv_mode() to umode_t * 2011-08-01 02:10:06 -04:00
inode.c vfs: fix spinning prevention in prune_icache_sb 2011-10-28 14:58:55 +02:00
internal.h superblock: move pin_sb_for_writeback() to fs/super.c 2011-07-20 01:44:38 -04:00
ioctl.c vfs: cleanup do_vfs_ioctl() 2011-03-21 00:16:08 -04:00
ioprio.c
Kconfig tmpfs: expand "help" to explain value of TMPFS_POSIX_ACL 2011-08-03 14:25:25 -10:00
Kconfig.binfmt
libfs.c fix IN_DELETE_SELF on overwriting rename() on ramfs et.al. 2011-07-22 19:42:11 -04:00
locks.c locks: rename lock-manager ops 2011-07-20 20:23:19 -04:00
Makefile nfsd: Remove deprecated nfsctl system call and related code. 2011-07-15 18:58:42 -04:00
mbcache.c vmscan: change shrinker API by passing shrink_control struct 2011-05-25 08:39:26 -07:00
mpage.c mm/fs: add hooks to support cleancache 2011-05-26 10:01:43 -06:00
namei.c vfs: add a comment to inode_permission() 2011-10-28 14:58:55 +02:00
namespace.c vfs: add "device" tag to /proc/self/mountstats 2011-10-28 13:55:08 +02:00
no-block.c
open.c merge fchmod() and fchmodat() guts, kill ancient broken kludge 2011-07-26 15:07:43 -04:00
pipe.c vfs: dont chain pipe/anon/socket on superblock s_inodes list 2011-07-26 12:57:09 -04:00
pnode.c fs: scale mntget/mntput 2011-01-07 17:50:33 +11:00
pnode.h
posix_acl.c vfs: pass all mask flags check_acl and posix_acl_permission 2011-10-28 14:58:54 +02:00
read_write.c vfs: do (nearly) lockless generic_file_llseek 2011-10-28 14:58:58 +02:00
read_write.h
readdir.c
select.c select: remove unused MAX_SELECT_SECONDS 2011-03-21 00:16:08 -04:00
seq_file.c
signalfd.c
splice.c tmpfs: clone shmem_file_splice_read() 2011-07-25 20:57:11 -07:00
stack.c mm: a few small updates for radix-swap 2011-08-03 14:25:24 -10:00
stat.c vfs: remove LOOKUP_NO_AUTOMOUNT flag 2011-09-27 08:12:33 -07:00
statfs.c clean statfs-like syscalls up 2011-03-14 09:15:28 -04:00
super.c Merge branch 'for-3.1/core' of git://git.kernel.dk/linux-block 2011-07-25 10:33:36 -07:00
sync.c fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers 2011-07-20 20:47:59 -04:00
timerfd.c timerfd: Fix wakeup of processes when timer is cancelled on clock change 2011-06-14 11:46:14 +02:00
utimes.c userns: rename is_owner_or_cap to inode_owner_or_capable 2011-03-23 19:47:13 -07:00
xattr.c Cache xattr security drop check for write v2 2011-05-28 12:02:09 -04:00
xattr_acl.c