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Subject: Re: [PATCH] mm: vmscan: correct nr_reclaimed for THP
To:     Matthew Wilcox <willy@infradead.org>
Cc:     "Huang, Ying" <ying.huang@intel.com>, 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>
 <3a919cba-fefe-d78e-313a-8f0d81a4a75d@linux.alibaba.com>
 <20190510165207.GB3162@bombadil.infradead.org>
From:   Yang Shi <yang.shi@linux.alibaba.com>
Message-ID: <72fb1554-4cda-27f4-8c09-038ab3350ff8@linux.alibaba.com>
Date:   Fri, 10 May 2019 09:54:11 -0700
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On 5/10/19 9:52 AM, Matthew Wilcox wrote:
> On Fri, May 10, 2019 at 09:50:04AM -0700, Yang Shi wrote:
>> 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?
> Yes.  Please, let's merge v1 and ignore v2.

Fine to me. I think Andrew will take care of it, Andrew?