linux-kernel - Re: [PATCH 2/3] zswap: dynamic pool creation

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Date:	Fri, 7 Aug 2015 15:30:56 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Dan Streetman <ddstreet@...e.org>
Cc:	Seth Jennings <sjennings@...iantweb.net>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] zswap: dynamic pool creation

Hello,

On (08/05/15 09:46), Dan Streetman wrote:
[..]
> -enum comp_op {
> -	ZSWAP_COMPOP_COMPRESS,
> -	ZSWAP_COMPOP_DECOMPRESS
> +struct zswap_pool {
> +	struct zpool *zpool;
> +	struct kref kref;
> +	struct list_head list;
> +	struct rcu_head rcu_head;
> +	struct notifier_block notifier;
> +	char tfm_name[CRYPTO_MAX_ALG_NAME];

do you need to keep a second CRYPTO_MAX_ALG_NAME copy? shouldn't it
be `tfm->__crt_alg->cra_name`, which is what
	crypto_tfm_alg_name(struct crypto_tfm *tfm)
does?

> +	struct crypto_comp * __percpu *tfm;
>  };

->tfm will be access pretty often, right? did you intentionally put it
at the bottom offset of `struct zswap_pool'?

[..]
> +static struct zswap_pool *__zswap_pool_current(void)
>  {
> -	return totalram_pages * zswap_max_pool_percent / 100 <
> -		DIV_ROUND_UP(zswap_pool_total_size, PAGE_SIZE);
> +	struct zswap_pool *pool;
> +
> +	pool = list_first_or_null_rcu(&zswap_pools, typeof(*pool), list);
> +	WARN_ON(!pool);
> +
> +	return pool;
> +}
> +
> +static struct zswap_pool *zswap_pool_current(void)
> +{
> +	assert_spin_locked(&zswap_pools_lock);
> +
> +	return __zswap_pool_current();
> +}

this one seems to be used only once. do you want to replace
that single usage (well, if it's really needed)

	WARN_ON(pool == zswap_pool_current());
with
	WARN_ON(pool == __zswap_pool_current);

?

you can then drop zswap_pool_current()... and probably rename
__zswap_pool_current() to zswap_pool_current().

	-ss

> +static struct zswap_pool *zswap_pool_current_get(void)
> +{
> +	struct zswap_pool *pool;
> +
> +	rcu_read_lock();
> +
> +	pool = __zswap_pool_current();
> +	if (!pool || !zswap_pool_get(pool))
> +		pool = NULL;
> +
> +	rcu_read_unlock();
> +
> +	return pool;
> +}
> +
> +static struct zswap_pool *zswap_pool_last_get(void)
> +{
> +	struct zswap_pool *pool, *last = NULL;
> +
> +	rcu_read_lock();
> +
> +	list_for_each_entry_rcu(pool, &zswap_pools, list)
> +		last = pool;
> +	if (!WARN_ON(!last) && !zswap_pool_get(last))
> +		last = NULL;
> +
> +	rcu_read_unlock();
> +
> +	return last;
> +}
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