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

Dave Chinner
2010-07-01T03:13:29Z

On Wed, Jun 30, 2010 at 10:08:50PM +1000, Nick Piggin wrote:
> 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.

Something like this doesn't seem particularly bad:

static inline struct list_head *
inode_get_sb_list(struct super_block *sb, int *i)
{
int cpu;

cpu = cpumask_next(i, cpu_possible_mask);
if (cpu >= nr_cpu_ids)
return NULL;
*i = cpu;
#ifdef CONFIG_SMP
return per_cpu_ptr(sb->s_inodes, cpu);
#else
return &sb->s_inodes;
#endif
}

and:

struct list_head *list;
int i;
....
i = -1;
while ((list = inode_get_sb_list(sb, &i))) {
list_for_each_entry_rcu(inode, tmp, list, i_sb_list) {
.....
}
}

I'd much prefer this to hiding the outer loop in macros...

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com