src/patches/suse-2.6.27.25/patches.suse/mnt_clone_write.patch

   1 From: Nick Piggin <npiggin@suse.de>
   2 Subject: fs: introduce mnt_clone_write
   3 References: bnc#436953
   4 Patch-upstream: no (could be submitted)
   5
   6 This patch speeds up lmbench lat_mmap test by about another 2% after the
   7 first patch.
   8
   9 Before:
  10  avg = 462.286
  11  std = 5.46106
  12
  13 After:
  14  avg = 453.12
  15  std = 9.58257
  16
  17 (50 runs of each, stddev gives a reasonable confidence)
  18
  19 It does this by introducing mnt_clone_write, which avoids some heavyweight
  20 operations of mnt_want_write if called on a vfsmount which we know already
  21 has a write count; and mnt_want_write_file, which can call mnt_clone_write
  22 if the file is open for write.
  23
  24 After these two patches, mnt_want_write and mnt_drop_write go from 7% on
  25 the profile down to 1.3% (including mnt_clone_write).
  26
  27 ---
  28  fs/file_table.c       |    3 +--
  29  fs/inode.c            |    2 +-
  30  fs/namespace.c        |   38 ++++++++++++++++++++++++++++++++++++++
  31  fs/open.c             |    4 ++--
  32  fs/xattr.c            |    4 ++--
  33  include/linux/mount.h |    2 ++
  34  6 files changed, 46 insertions(+), 7 deletions(-)
  35
  36 --- a/fs/file_table.c
  37 +++ b/fs/file_table.c
  38 @@ -210,8 +210,7 @@ int init_file(struct file *file, struct
  39          */
  40         if ((mode & FMODE_WRITE) && !special_file(dentry->d_inode->i_mode)) {
  41                 file_take_write(file);
  42 -               error = mnt_want_write(mnt);
  43 -               WARN_ON(error);
  44 +               mnt_clone_write(mnt);
  45         }
  46         return error;
  47  }
  48 --- a/fs/inode.c
  49 +++ b/fs/inode.c
  50 @@ -1256,7 +1256,7 @@ void file_update_time(struct file *file)
  51         if (IS_NOCMTIME(inode))
  52                 return;
  53
  54 -       err = mnt_want_write(file->f_path.mnt);
  55 +       err = mnt_want_write_file(file->f_path.mnt, file);
  56         if (err)
  57                 return;
  58
  59 --- a/fs/namespace.c
  60 +++ b/fs/namespace.c
  61 @@ -264,6 +264,44 @@ out:
  62  EXPORT_SYMBOL_GPL(mnt_want_write);
  63
  64  /**
  65 + * mnt_clone_write - get write access to a mount
  66 + * @mnt: the mount on which to take a write
  67 + *
  68 + * This is effectively like mnt_want_write, except
  69 + * it must only be used to take an extra write reference
  70 + * on a mountpoint that we already know has a write reference
  71 + * on it. This allows some optimisation.
  72 + *
  73 + * After finished, mnt_drop_write must be called as usual to
  74 + * drop the reference.
  75 + */
  76 +void mnt_clone_write(struct vfsmount *mnt)
  77 +{
  78 +       preempt_disable();
  79 +       inc_mnt_writers(mnt);
  80 +       preempt_enable();
  81 +}
  82 +EXPORT_SYMBOL_GPL(mnt_clone_write);
  83 +
  84 +/**
  85 + * mnt_want_write_file - get write access to a file's mount
  86 + * @file: the file who's mount on which to take a write
  87 + *
  88 + * This is like mnt_want_write, but it takes a file and can
  89 + * do some optimisations if the file is open for write already
  90 + */
  91 +int mnt_want_write_file(struct vfsmount *mnt, struct file *file)
  92 +{
  93 +       if (!(file->f_mode & FMODE_WRITE))
  94 +               return mnt_want_write(mnt);
  95 +       else {
  96 +               mnt_clone_write(mnt);
  97 +               return 0;
  98 +       }
  99 +}
 100 +EXPORT_SYMBOL_GPL(mnt_want_write_file);
 101 +
 102 +/**
 103   * mnt_drop_write - give up write access to a mount
 104   * @mnt: the mount on which to give up write access
 105   *
 106 --- a/fs/open.c
 107 +++ b/fs/open.c
 108 @@ -616,7 +616,7 @@ SYSCALL_DEFINE2(fchmod, unsigned int, fd
 109
 110         audit_inode(NULL, dentry);
 111
 112 -       err = mnt_want_write(file->f_path.mnt);
 113 +       err = mnt_want_write_file(file->f_path.mnt, file);
 114         if (err)
 115                 goto out_putf;
 116         mutex_lock(&inode->i_mutex);
 117 @@ -765,7 +765,7 @@ SYSCALL_DEFINE3(fchown, unsigned int, fd
 118         if (!file)
 119                 goto out;
 120
 121 -       error = mnt_want_write(file->f_path.mnt);
 122 +       error = mnt_want_write_file(file->f_path.mnt, file);
 123         if (error)
 124                 goto out_fput;
 125         dentry = file->f_path.dentry;
 126 --- a/fs/xattr.c
 127 +++ b/fs/xattr.c
 128 @@ -301,7 +301,7 @@ SYSCALL_DEFINE5(fsetxattr, int, fd, cons
 129                 return error;
 130         dentry = f->f_path.dentry;
 131         audit_inode(NULL, dentry);
 132 -       error = mnt_want_write(f->f_path.mnt);
 133 +       error = mnt_want_write_file(f->f_path.mnt, f);
 134         if (!error) {
 135                 error = setxattr(dentry, name, value, size, flags);
 136                 mnt_drop_write(f->f_path.mnt);
 137 @@ -528,7 +528,7 @@ SYSCALL_DEFINE2(fremovexattr, int, fd, c
 138                 return error;
 139         dentry = f->f_path.dentry;
 140         audit_inode(NULL, dentry);
 141 -       error = mnt_want_write(f->f_path.mnt);
 142 +       error = mnt_want_write_file(f->f_path.mnt, f);
 143         if (!error) {
 144                 error = removexattr(dentry, name);
 145                 mnt_drop_write(f->f_path.mnt);
 146 --- a/include/linux/mount.h
 147 +++ b/include/linux/mount.h
 148 @@ -99,6 +99,8 @@ static inline struct vfsmount *mntget(st
 149  }
 150
 151  extern int mnt_want_write(struct vfsmount *mnt);
 152 +extern int mnt_want_write_file(struct vfsmount *mnt, struct file *file);
 153 +extern void mnt_clone_write(struct vfsmount *mnt);
 154  extern void mnt_drop_write(struct vfsmount *mnt);
 155  extern void mntput_no_expire(struct vfsmount *mnt);
 156  extern void mnt_pin(struct vfsmount *mnt);