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Subject: Re: [patch 01/52] kernel: add bl_list
From: Eric Dumazet <eric.dumazet@gmail.com>
To: npiggin@suse.de
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
       John Stultz <johnstul@us.ibm.com>, Frank Mayhar <fmayhar@google.com>
In-Reply-To: <20100624030725.718438579@suse.de>
References: <20100624030212.676457061@suse.de>
	 <20100624030725.718438579@suse.de>
Content-Type: text/plain; charset="UTF-8"
Date: Thu, 24 Jun 2010 08:04:22 +0200
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Sender: linux-kernel-owner@vger.kernel.org
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Le jeudi 24 juin 2010 à 13:02 +1000, npiggin@suse.de a écrit :
> pièce jointe document texte brut (list-bitlock.patch)
> Introduce a type of hlist that can support the use of the lowest bit in the
> hlist_head. This will be subsequently used to implement per-bucket bit spinlock
> for inode and dentry hashes.
> 
> Signed-off-by: Nick Piggin <npiggin@suse.de>
> 
> ---
>  include/linux/list_bl.h    |   99 +++++++++++++++++++++++++++++++++++++
>  include/linux/rculist_bl.h |  120 +++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 219 insertions(+)
> 
> Index: linux-2.6/include/linux/list_bl.h
> ===================================================================
> --- /dev/null
> +++ linux-2.6/include/linux/list_bl.h
> @@ -0,0 +1,99 @@
> +#ifndef _LINUX_LIST_BL_H
> +#define _LINUX_LIST_BL_H
> +
> +#include <linux/list.h>
> +
> +/*
> + * Special version of lists, where head of the list has a bit spinlock
> + * in the lowest bit. This is useful for scalable hash tables without
> + * increasing memory footprint overhead.
> + */
> +
> +struct hlist_bl_head {
> +	struct hlist_bl_node *first;
> +};
> +
> +struct hlist_bl_node {
> +	struct hlist_bl_node *next, **pprev;
> +};
> +#define INIT_HLIST_BL_HEAD(ptr) \
> +	((ptr)->first = NULL)
> +
> +static inline void INIT_HLIST_BL_NODE(struct hlist_bl_node *h)
> +{
> +	h->next = NULL;
> +	h->pprev = NULL;
> +}
> +
> +#define hlist_bl_entry(ptr, type, member) container_of(ptr,type,member)
> +
> +static inline int hlist_bl_unhashed(const struct hlist_bl_node *h)
> +{
> +	return !h->pprev;
> +}
> +
> +static inline struct hlist_bl_node *hlist_bl_first(struct hlist_bl_head *h)
> +{
> +	return (struct hlist_bl_node *)((unsigned long)h->first & ~1UL);
> +}
> +
> +static inline void hlist_bl_set_first(struct hlist_bl_head *h, struct hlist_bl_node *n)
> +{
> +	h->first = (struct hlist_bl_node *)((unsigned long)n | ((unsigned long)h->first & 1UL));

Hmm, shouldnt hlist_bl_set_first() be used only with bit lock held ?

	h->first = (struct hlist_bl_node *)((unsigned long)n | 1UL);
> +}
> +

> +
> +static inline void hlist_bl_set_first_rcu(struct hlist_bl_head *h, struct hlist_bl_node *n)
> +{
> +	rcu_assign_pointer(h->first, (struct hlist_bl_node *)((unsigned long)n | ((unsigned long)h->first & 1UL)));

Same question here.

> +}
> +
> +static inline struct hlist_bl_node *hlist_bl_first_rcu(struct hlist_bl_head *h)
> +{
> +	return (struct hlist_bl_node *)((unsigned long)rcu_dereference(h->first) & ~1UL);
> +}


Looks really nice Nick, maybe we should push this so that other
subsystem can start using it.

Thanks


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