linux-kernel - RE: [PATCH 8/8] mm/zswap: Use local lock to protect per-CPU data

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Message-ID: <B926444035E5E2439431908E3842AFD24AFEC5@DGGEMI525-MBS.china.huawei.com>
Date:   Tue, 19 May 2020 21:46:06 +0000
From:   Song Bao Hua <song.bao.hua@...ilicon.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Luis Claudio R. Goncalves" <lgoncalv@...hat.com>,
        Seth Jennings <sjenning@...hat.com>,
        Dan Streetman <ddstreet@...e.org>,
        Vitaly Wool <vitaly.wool@...sulko.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Linuxarm <linuxarm@...wei.com>
Subject: RE: [PATCH 8/8] mm/zswap: Use local lock to protect per-CPU data


> From: "Luis Claudio R. Goncalves" <lgoncalv@...hat.com>

> zwap uses per-CPU compression. The per-CPU data pointer is acquired with
> get_cpu_ptr() which implicitly disables preemption. It allocates memory inside the preempt disabled region which conflicts with the PREEMPT_RT semantics.

> Replace the implicit preemption control with an explicit local lock.
> This allows RT kernels to substitute it with a real per CPU lock, which serializes the access but keeps the code section preemptible. On non RT kernels this maps to preempt_disable() as before, i.e. no functional change.

Hi Luis,
In the below patch, in order to use the acomp APIs to leverage the power of hardware compressors. I have moved to mutex:
https://marc.info/?l=linux-crypto-vger&m=158941285830302&w=2
https://marc.info/?l=linux-crypto-vger&m=158941287930311&w=2

so once we get some progress on that one, I guess we don't need a special patch for RT any more.

> [bigeasy: Use local_lock(), additional hunks, patch description]

> Cc: Seth Jennings <sjenning@...hat.com>
> Cc: Dan Streetman <ddstreet@...e.org>
> Cc: Vitaly Wool <vitaly.wool@...sulko.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: linux-mm@...ck.org
> Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@...hat.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  mm/zswap.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)

Thanks
Barry