Re: [patch 44/52] fs: icache per-CPU sb inode lists and locks

Nick Piggin
2010-06-30T14:33:27Z

On Wed, Jun 30, 2010 at 07:26:41PM +1000, Dave Chinner wrote:
> On Thu, Jun 24, 2010 at 01:02:56PM +1000, npiggin@suse.de wrote:
> > Signed-off-by: Nick Piggin <npiggin@suse.de>
> .....
> > @@ -2194,6 +2198,58 @@ static inline void insert_inode_hash(str
> >
> > extern void file_sb_list_add(struct file *f, struct super_block *sb);
> > extern void file_sb_list_del(struct file *f);
> > +#ifdef CONFIG_SMP
> > +
> > +/*
> > + * These macros iterate all inodes on all CPUs for a given superblock.
> > + * rcu_read_lock must be held.
> > + */
> > +#define do_inode_list_for_each_entry_rcu(__sb, __inode) \
> > +{ \
> > + int i; \
> > + for_each_possible_cpu(i) { \
> > + struct list_head *list; \
> > + list = per_cpu_ptr((__sb)->s_inodes, i); \
> > + list_for_each_entry_rcu((__inode), list, i_sb_list)
> > +
> > +#define while_inode_list_for_each_entry_rcu \
> > + } \
> > +}
> > +
> > +#define do_inode_list_for_each_entry_safe(__sb, __inode, __tmp) \
> > +{ \
> > + int i; \
> > + for_each_possible_cpu(i) { \
> > + struct list_head *list; \
> > + list = per_cpu_ptr((__sb)->s_inodes, i); \
> > + list_for_each_entry_safe((__inode), (__tmp), list, i_sb_list)
> > +
> > +#define while_inode_list_for_each_entry_safe \
> > + } \
> > +}
> > +
> > +#else
> > +
> > +#define do_inode_list_for_each_entry_rcu(__sb, __inode) \
> > +{ \
> > + struct list_head *list; \
> > + list = &(sb)->s_inodes; \
> > + list_for_each_entry_rcu((__inode), list, i_sb_list)
> > +
> > +#define while_inode_list_for_each_entry_rcu \
> > +}
> > +
> > +#define do_inode_list_for_each_entry_safe(__sb, __inode, __tmp) \
> > +{ \
> > + struct list_head *list; \
> > + list = &(sb)->s_inodes; \
> > + list_for_each_entry_rcu((__inode), (__tmp), list, i_sb_list)
> > +
> > +#define while_inode_list_for_each_entry_safe \
> > +}
>
> I can't say that I'm a great fan of hiding loop context in defines
> like this. It reminds far too much of how parts of Irix slowly
> ossified because they ended up mess of complex, fragile macros that
> nobody fully understood...

It's not perfect. I think it is a lot better than open coding
(which I tried before) because that really muddies up the intention
of the loop body.