linux-kernel - Re: [PATCH] zsmalloc: do not use bit_spin

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Message-ID: <CAM4kBBJCONeSBUwnH0rb3-cAn5THDFapQ8p8xt6+-VaobS_cWg@mail.gmail.com>
Date:   Sun, 20 Dec 2020 08:21:37 +0100
From:   Vitaly Wool <vitaly.wool@...sulko.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Mike Galbraith <efault@....de>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Minchan Kim <minchan@...nel.org>,
        NitinGupta <ngupta@...are.org>
Subject: Re: [PATCH] zsmalloc: do not use bit_spin_lock

On Sun, Dec 20, 2020 at 2:18 AM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Sun, Dec 20, 2020 at 02:22:28AM +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.
>
> Isn't this just "I open coded bit spinlock to make the lockdep
> warnings go away"?

Not really because bit spinlock leaves preemption disabled.