Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH] mm: vmscan: correct nr_reclaimed for THP
To:     Matthew Wilcox <willy@infradead.org>,
        "Huang, Ying" <ying.huang@intel.com>
Cc:     hannes@cmpxchg.org, mhocko@suse.com, mgorman@techsingularity.net,
        kirill.shutemov@linux.intel.com, hughd@google.com,
        akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <1557447392-61607-1-git-send-email-yang.shi@linux.alibaba.com>
 <87y33fjbvr.fsf@yhuang-dev.intel.com>
 <20190510163612.GA23417@bombadil.infradead.org>
From:   Yang Shi <yang.shi@linux.alibaba.com>
Message-ID: <3a919cba-fefe-d78e-313a-8f0d81a4a75d@linux.alibaba.com>
Date:   Fri, 10 May 2019 09:50:04 -0700
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0)
 Gecko/20100101 Thunderbird/52.7.0
MIME-Version: 1.0
In-Reply-To: <20190510163612.GA23417@bombadil.infradead.org>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Content-Language: en-US
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


On 5/10/19 9:36 AM, Matthew Wilcox wrote:
> On Fri, May 10, 2019 at 10:12:40AM +0800, Huang, Ying wrote:
>>> +		nr_reclaimed += (1 << compound_order(page));
>> How about to change this to
>>
>>
>>          nr_reclaimed += hpage_nr_pages(page);
> Please don't.  That embeds the knowledge that we can only swap out either
> normal pages or THP sized pages.  I'm trying to make the VM capable of
> supporting arbitrary-order pages, and this would be just one more place
> to fix.
>
> I'm sympathetic to the "self documenting" argument.  My current tree has
> a patch in it:
>
>      mm: Introduce compound_nr
>      
>      Replace 1 << compound_order(page) with compound_nr(page).  Minor
>      improvements in readability.
>
> It goes along with this patch:
>
>      mm: Introduce page_size()
>
>      It's unnecessarily hard to find out the size of a potentially huge page.
>      Replace 'PAGE_SIZE << compound_order(page)' with page_size(page).

So you prefer keeping using  "1 << compound_order" as v1 did? Then you 
will convert all "1 << compound_order" to compound_nr?

>
> Better suggestions on naming gratefully received.  I'm more happy with
> page_size() than I am with compound_nr().  page_nr() gives the wrong
> impression; page_count() isn't great either.