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:   Thu, 23 Apr 2020 13:00:20 -0700
From:   Minchan Kim <minchan@kernel.org>
To:     Johannes Weiner <hannes@cmpxchg.org>
Cc:     Jaewon Kim <jaewon31.kim@samsung.com>, mgorman@suse.de,
        m.szyprowski@samsung.com, mina86@mina86.com, shli@fb.com,
        akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, jaewon31.kim@gmail.com,
        ytk.lee@samsung.com
Subject: Re: [PATCH v2] mm/vmscan: count layzfree pages and fix nr_isolated_*
 mismatch
Message-ID: <20200423200020.GB46847@google.com>
References: <CGME20200422084832epcas1p333225f9b6a00c9ce36f5f5d63fe6e3bf@epcas1p3.samsung.com>
 <20200422084815.21913-1-jaewon31.kim@samsung.com>
 <20200422130751.GD358439@cmpxchg.org>
 <5EA10872.3010500@samsung.com>
 <20200423160546.GA389168@cmpxchg.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <20200423160546.GA389168@cmpxchg.org>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Apr 23, 2020 at 12:05:46PM -0400, Johannes Weiner wrote:
> On Thu, Apr 23, 2020 at 12:16:02PM +0900, Jaewon Kim wrote:
> > 
> > 
> > On 2020년 04월 22일 22:07, Johannes Weiner wrote:
> > > On Wed, Apr 22, 2020 at 05:48:15PM +0900, Jaewon Kim wrote:
> > >> @@ -1295,11 +1295,15 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> > >>  		 */
> > >>  		if (page_mapped(page)) {
> > >>  			enum ttu_flags flags = ttu_flags | TTU_BATCH_FLUSH;
> > >> +			bool lazyfree = PageAnon(page) && !PageSwapBacked(page);
> > >>  
> > >>  			if (unlikely(PageTransHuge(page)))
> > >>  				flags |= TTU_SPLIT_HUGE_PMD;
> > >> +
> > >>  			if (!try_to_unmap(page, flags)) {
> > >>  				stat->nr_unmap_fail += nr_pages;
> > >> +				if (lazyfree && PageSwapBacked(page))
> > > This looks pretty strange, until you remember that try_to_unmap()
> > > could SetPageSwapbacked again.
> > >
> > > This might be more obvious?
> > >
> > > 			was_swapbacked = PageSwapBacked(page);
> > > 			if (!try_to_unmap(page, flags)) {
> > > 				stat->nr_unmap_fail += nr_pages;
> > > 				if (!was_swapbacked && PageSwapBacked(page))
> > Hello Johannes, thank you for your comment.
> > 
> > The name can changed from layzyfree to was_swapbacked.
> > By the way, did you mean removing PageAnon(page), too? It seems to be OK, though.
> 
> I can't decide whether PageAnon() makes it clearer or not. But it's
> not really needed for correctness. So feel free to keep what you had.

Yub, PageAnon is redundant.

> I would really just at least change bool lazyfree to was_lazyfree,

It's better.