[PATCH] : struct dentry : place d_hash close to d_parent and d_name to speedup lookups

• To: Andrew Morton <[email protected]>, [email protected]
• Subject: [PATCH] : struct dentry : place d_hash close to d_parent and d_name to speedup lookups
• From: Eric Dumazet <[email protected]>
• Date: Thu, 01 Sep 2005 17:44:48 +0200
• In-reply-to: <[email protected]>
• References: <[email protected]>
• Sender: [email protected]
• User-agent: Mozilla Thunderbird 1.0 (Windows/20041206)

dentry cache uses sophisticated RCU technology (and prefetching if available) but touches 2 cache lines per dentry during hlist lookup.

This patch moves d_hash in the same cache line than d_parent and d_name fields so that :

1) One cache line is needed instead of two.

2) the hlist_for_each_rcu() prefetching has a chance to bring all the needed data in advance, not only the part that includes d_hash.next.

I also changed one old comment that was wrong for 64bits.

A further optimisation would be to separate dentry in two parts, one that is mostly read, and one writen (d_count/d_lock) to avoid false sharing on SMP/NUMA but this would need different field placement depending on 32bits or 64bits platform.

Signed-off-by: Eric Dumazet <[email protected]>

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    • From: Eric Dumazet <[email protected]>

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    • From: Andrew Morton <[email protected]>

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