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Date:   Fri, 10 May 2019 15:54:56 -0700
From:   Ira Weiny <ira.weiny@intel.com>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     "Huang, Ying" <ying.huang@intel.com>,
        Yang Shi <yang.shi@linux.alibaba.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
Subject: Re: [PATCH] mm: vmscan: correct nr_reclaimed for THP
Message-ID: <20190510225456.GA13529@iweiny-DESK2.sc.intel.com>
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 <87y33fjbvr.fsf@yhuang-dev.intel.com>
 <20190510163612.GA23417@bombadil.infradead.org>
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On Fri, May 10, 2019 at 09:36:12AM -0700, 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).
> 
> 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.

Stupid question : what does 'nr' stand for?

Ira