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, 24 Apr 2020 09:17:56 -0400
From:   Johannes Weiner <hannes@cmpxchg.org>
To:     Jaewon Kim <jaewon31.kim@samsung.com>
Cc:     Minchan Kim <minchan@kernel.org>, 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: <20200424131756.GB495720@cmpxchg.org>
References: <CGME20200422084832epcas1p333225f9b6a00c9ce36f5f5d63fe6e3bf@epcas1p3.samsung.com>
 <20200422084815.21913-1-jaewon31.kim@samsung.com>
 <20200422130751.GD358439@cmpxchg.org>
 <5EA10872.3010500@samsung.com>
 <20200423160546.GA389168@cmpxchg.org>
 <20200423200020.GB46847@google.com>
 <5EA2682D.7010307@samsung.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <5EA2682D.7010307@samsung.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Apr 24, 2020 at 01:16:45PM +0900, Jaewon Kim wrote:
> 
> 
> On 2020년 04월 24일 05:00, Minchan Kim wrote:
> > 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.
> Thank you both.
> 
> Sorry but let me ask again.
> 
> Because PageAnon is redundant, let me remove it on checking lazyfree.
> Then, I think, was_swapbacked (first suggestion) is better then was_lazyfree (second suggestion),
> because it just checks PageSwapBacked(page). And we knows was_swapbacked is used for lazyfree on stat->nr_lazyfree_fail.
> 
> If you don't mind let me pick was_swapbacked instead of was_lazyfree

That sounds good to me. Thanks Jaewon!