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Message-ID: <5f72f88c55e3365883f597c01dc471520281d8d3.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 05:11:48 +0100
In-Reply-To: <c9c97ae293f5d7321ff30ac6ead49751560dd354.camel@gmx.de>
References: <18669bd607ae9efbf4e00e36532c7aa167d0fa12.camel@gmx.de>
         <20201220002228.38697-1-vitaly.wool@konsulko.com>
         <c9c97ae293f5d7321ff30ac6ead49751560dd354.camel@gmx.de>
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On Sun, 2020-12-20 at 02:23 +0100, Mike Galbraith wrote:
> 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.
>
> It also does get_cpu_var() in map(), put_cpu_var() in unmap().

Bah, I forgot to mention the config dependent rwlock, it's held across
map()/unmap() as well, so there are two more hurdles, not one.

	-Mike