Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <53dd6a82bbb2a9a102b420899281633a3e1b37a8.camel@gmx.de>
Subject: Re: [PATCH] zsmalloc: do not use bit_spin_lock
From:   Mike Galbraith <efault@gmx.de>
To:     Vitaly Wool <vitaly.wool@konsulko.com>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>
Cc:     Barry Song <song.bao.hua@hisilicon.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Minchan Kim <minchan@kernel.org>,
        NitinGupta <ngupta@vflare.org>
Date:   Sun, 20 Dec 2020 02:56:18 +0100
In-Reply-To: <20201220002228.38697-1-vitaly.wool@konsulko.com>
References: <18669bd607ae9efbf4e00e36532c7aa167d0fa12.camel@gmx.de>
         <20201220002228.38697-1-vitaly.wool@konsulko.com>
Content-Type: text/plain; charset="ISO-8859-15"
User-Agent: Evolution 3.34.4 
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Sun, 2020-12-20 at 02:22 +0200, Vitaly Wool wrote:
> zsmalloc takes bit spinlock in its _map() callback and releases it
> only in unmap() which is unsafe and leads to zswap complaining
> about scheduling in atomic context.
>
> To fix that and to improve RT properties of zsmalloc, remove that
> bit spinlock completely and use a bit flag instead.


> -static void pin_tag(unsigned long handle) __acquires(bitlock)
> +static void pin_tag(unsigned long handle)
>  {
> -	bit_spin_lock(HANDLE_PIN_BIT, (unsigned long *)handle);
> +	preempt_disable();
> +	while(test_and_set_bit(HANDLE_PIN_BIT, (unsigned long *)handle))
> +		cpu_relax();
> +	preempt_enable();
>  }

If try doesn't need to disable preemption, neither does pin.

	-Mike