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Subject: Re: [PATCH v2 6/8] mm/lru: remove rcu_read_lock to fix performance
 regression
To:     Matthew Wilcox <willy@infradead.org>
Cc:     cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, akpm@linux-foundation.org,
        mgorman@techsingularity.net, tj@kernel.org, hughd@google.com,
        khlebnikov@yandex-team.ru, daniel.m.jordan@oracle.com,
        yang.shi@linux.alibaba.com, Johannes Weiner <hannes@cmpxchg.org>,
        Roman Gushchin <guro@fb.com>,
        Shakeel Butt <shakeelb@google.com>,
        Chris Down <chris@chrisdown.name>,
        Thomas Gleixner <tglx@linutronix.de>
References: <1573567588-47048-1-git-send-email-alex.shi@linux.alibaba.com>
 <1573567588-47048-7-git-send-email-alex.shi@linux.alibaba.com>
 <20191112143844.GB7934@bombadil.infradead.org>
From:   Alex Shi <alex.shi@linux.alibaba.com>
Message-ID: <a6bb6739-cc00-cf9f-cd69-6016ce93e054@linux.alibaba.com>
Date:   Wed, 13 Nov 2019 10:40:58 +0800
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?? 2019/11/12 ????10:38, Matthew Wilcox д??:
> On Tue, Nov 12, 2019 at 10:06:26PM +0800, Alex Shi wrote:
>> Intel 0day report there are performance regression on this patchset.
>> The detailed info points to rcu_read_lock + PROVE_LOCKING which causes
>> queued_spin_lock_slowpath waiting too long time to get lock.
>> Remove rcu_read_lock is safe here since we had a spinlock hold.
> Argh.  You have not sent these patches in a properly reviewable form!
> I wasted all that time reviewing the earlier patch in this series only to
> find out that you changed it here.  FIX THE PATCH, don't send a fix-patch
> on top of it!
> 

Hi Matthew,

Very sorry for your time! The main reasons I use a separate patch since a, Intel 0day asking me to credit their are founding, and I don't know how to give a clearly/elegant explanation for a non-exist regression in a fixed patch. b, this regression is kindly pretty tricky.  Maybe it's better saying thanks in version change log of cover-letter?

Anyway, Thanks a lot for your review!

Alex