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Date: Wed, 30 Jun 2010 22:08:50 +1000
From: Nick Piggin <npiggin@suse.de>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
       John Stultz <johnstul@us.ibm.com>, Frank Mayhar <fmayhar@google.com>
Subject: Re: [patch 44/52] fs: icache per-CPU sb inode lists and locks
Message-ID: <20100630120850.GE21358@laptop>
References: <20100624030212.676457061@suse.de>
 <20100624030732.702284052@suse.de>
 <20100630092641.GI24712@dastard>
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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.