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;
Date:   Fri, 1 Oct 2021 12:43:56 -0400
From:   Johannes Weiner <hannes@cmpxchg.org>
To:     =?utf-8?B?6KejIOWSj+aihQ==?= <yongmeixie@hotmail.com>
Cc:     "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: =?utf-8?B?5Zue5aSNOiBbUEFUQ0hdIG1tOnZt?=
 =?utf-8?Q?scan=3A_fix_extra_adjustmen?= =?utf-8?Q?t?= for lruvec's
 nonresident_age in case of reactivation
Message-ID: <YVc6zOy51aaRgw2y@cmpxchg.org>
References: <TYCP286MB1108D012DA436CA72029ACA7C5DF9@TYCP286MB1108.JPNP286.PROD.OUTLOOK.COM>
 <YUnwsyE87TViMNMz@cmpxchg.org>
 <TYYP286MB11150330E283CC23CB16E40CC5A29@TYYP286MB1115.JPNP286.PROD.OUTLOOK.COM>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <TYYP286MB11150330E283CC23CB16E40CC5A29@TYYP286MB1115.JPNP286.PROD.OUTLOOK.COM>
Precedence: bulk

On Wed, Sep 22, 2021 at 02:27:24PM +0000, 解 咏梅 wrote:
> But now, move_pages_to_lru didn't increase nonresident age for active rotation.
> Back toinactive age, VM ONLY care about the pages left inactive lru, AKA activation and reclaiming.
> Anyway reactivation is rare case, so whatever it contributes to nonresident age or not is ok to me.
> 
> But I am interested the logic how to guess the pages will be referenced again in the future.
> If active reactivation does matter to nonresident age. why not active rotation? But, currently it doesn't.

Can you point me to the code you're referring to? Looking at
move_pages_to_lru(), any pages with PageActive() set count toward the
non-resident age. That means activations from the inactive list, as
well as rotations on the active list, increase the nonresident age.

As to your question which one is right: the original workingset patch
was wrong not to count activations and reactivations. If we see a page
referenced in memory, it means it's hotter than the page that's not
refaulting -> nonresident age increses.

So the code as it is now looks correct to me.

Thanks