On Sat, Apr 27, 2013 at 03:19:00AM +0400, Glauber Costa wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> With the dentry LRUs being per-sb structures, there is no real need
> for a global dentry_lru_lock. The locking can be made more
> fine-grained by moving to a per-sb LRU lock, isolating the LRU
> operations of different filesytsems completely from each other.
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxx>
But one comment below
> @@ -81,7 +81,6 @@
> int sysctl_vfs_cache_pressure __read_mostly = 100;
> EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
>
> -static __cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_lru_lock);
> __cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);
>
> EXPORT_SYMBOL(rename_lock);
It made sense to cache-align these locks because you don't want two
unrelated global locks causing each other to bounce but ....
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 8d47c9a..df3174d 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1263,7 +1263,9 @@ struct super_block {
> struct list_head s_files;
> #endif
> struct list_head s_mounts; /* list of mounts; _not_ for fs use */
> - /* s_dentry_lru, s_nr_dentry_unused protected by dcache.c lru locks */
> +
> + /* s_dentry_lru_lock protects s_dentry_lru and s_nr_dentry_unused */
> + spinlock_t s_dentry_lru_lock ____cacheline_aligned_in_smp;
> struct list_head s_dentry_lru; /* unused dentry lru */
> int s_nr_dentry_unused; /* # of dentry on lru */
>
It's less compelling to align within a structure like this. If move the
lock and the fields it protects to a read-mostly section then there
should be no need to cache-align the lock, create a large hole in the
struct and grow the size of struct super_block unnecessarily.
--
Mel Gorman
SUSE Labs
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