linux-kernel - Re: [PATCH] mm: vmscan: correct nr

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Date:   Fri, 10 May 2019 09:52:07 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Yang Shi <yang.shi@...ux.alibaba.com>
Cc:     "Huang, Ying" <ying.huang@...el.com>, hannes@...xchg.org,
        mhocko@...e.com, mgorman@...hsingularity.net,
        kirill.shutemov@...ux.intel.com, hughd@...gle.com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: vmscan: correct nr_reclaimed for THP

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.