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Subject: Re: [PATCH] mm: vmscan: correct nr_reclaimed for THP
From:   William Kucharski <william.kucharski@oracle.com>
In-Reply-To: <20190510163612.GA23417@bombadil.infradead.org>
Date:   Sat, 11 May 2019 16:33:01 -0600
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
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Message-Id: <7B762A95-B8A6-4281-94F1-5DA6B62EDCF9@oracle.com>
References: <1557447392-61607-1-git-send-email-yang.shi@linux.alibaba.com>
 <87y33fjbvr.fsf@yhuang-dev.intel.com>
 <20190510163612.GA23417@bombadil.infradead.org>
To:     Matthew Wilcox <willy@infradead.org>
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> On May 10, 2019, at 10:36 AM, Matthew Wilcox <willy@infradead.org> =
wrote:
>=20
> Please don't.  That embeds the knowledge that we can only swap out =
either=20
> normal pages or THP sized pages.  I'm trying to make the VM capable of=20=

> supporting arbitrary-order pages, and this would be just one more =
place
> to fix.
>=20
> I'm sympathetic to the "self documenting" argument.  My current tree =
has
> a patch in it:
>=20
>    mm: Introduce compound_nr
>=20
>    Replace 1 << compound_order(page) with compound_nr(page).  Minor
>    improvements in readability.
>=20
> It goes along with this patch:
>=20
>    mm: Introduce page_size()
>=20
>    It's unnecessarily hard to find out the size of a potentially huge =
page.
>    Replace 'PAGE_SIZE << compound_order(page)' with page_size(page).
>=20
> Better suggestions on naming gratefully received.  I'm more happy with=20=

> page_size() than I am with compound_nr().  page_nr() gives the wrong
> impression; page_count() isn't great either.

I like page_size() as well. At least to me, page_nr() or page_count() =
would
imply a basis of PAGESIZE, or that you would need to do something like:

    page_size =3D page_nr() << PAGE_SHIFT;

to get the size in bytes; page_size() is more straightforward in that =
respect.=