linux-kernel - Re: [PATCH v2 1/3] zram: Replace bit spinlocks with a spinlock

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Message-ID: <27fb4f62-d656-449c-9f3c-5d0b61a88cca@intel.com>
Date: Thu, 4 Jul 2024 13:38:04 +0200
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC: <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Minchan Kim
	<minchan@...nel.org>, Sergey Senozhatsky <senozhatsky@...omium.org>, "Jens
 Axboe" <axboe@...nel.dk>, Thomas Gleixner <tglx@...utronix.de>, Mike
 Galbraith <umgwanakikbuti@...il.com>
Subject: Re: [PATCH v2 1/3] zram: Replace bit spinlocks with a spinlock_t.

From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Date: Thu, 20 Jun 2024 17:28:50 +0200

> From: Mike Galbraith <umgwanakikbuti@...il.com>
> 
> The bit spinlock disables preemption. The spinlock_t lock becomes a sleeping
> lock on PREEMPT_RT and it can not be acquired in this context. In this locked
> section, zs_free() acquires a zs_pool::lock, and there is access to
> zram::wb_limit_lock.
> 
> Add a spinlock_t for locking. Keep the set/ clear ZRAM_LOCK bit after
> the lock has been acquired/ dropped. The size of struct zram_table_entry
> increases by 4 bytes due to lock and additional 4 bytes padding with
> CONFIG_ZRAM_TRACK_ENTRY_ACTIME enabled.
> 
> Signed-off-by: Mike Galbraith <umgwanakikbuti@...il.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  drivers/block/zram/zram_drv.c | 22 +++++++++++++++++++---
>  drivers/block/zram/zram_drv.h |  1 +
>  2 files changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 3acd7006ad2cc..036845cd4f25e 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -57,19 +57,34 @@ static void zram_free_page(struct zram *zram, size_t index);
>  static int zram_read_page(struct zram *zram, struct page *page, u32 index,
>  			  struct bio *parent);
>  
> +static void zram_meta_init_table_locks(struct zram *zram, size_t num_pages)
> +{
> +	size_t index;
> +
> +	for (index = 0; index < num_pages; index++)

Maybe declare @index right here?

> +		spin_lock_init(&zram->table[index].lock);
> +}

[...]

Thanks,
Olek