linux-kernel - Re: [RFC PATCH 3/6] mm: page_owner: add support for splitting to any order in split page

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Message-ID: <20201117211001.GY29991@casper.infradead.org>
Date:   Tue, 17 Nov 2020 21:10:01 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Zi Yan <ziy@...dia.com>
Cc:     linux-mm@...ck.org,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Roman Gushchin <guro@...com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Yang Shi <shy828301@...il.com>,
        Michal Hocko <mhocko@...nel.org>,
        John Hubbard <jhubbard@...dia.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        David Nellans <dnellans@...dia.com>
Subject: Re: [RFC PATCH 3/6] mm: page_owner: add support for splitting to any
 order in split page_owner.

On Wed, Nov 11, 2020 at 03:40:05PM -0500, Zi Yan wrote:
> -	for (i = 0; i < nr; i++) {
> +	for (i = 0; i < nr; i += (1 << new_order)) {
>  		page_owner = get_page_owner(page_ext);
> -		page_owner->order = 0;
> +		page_owner->order = new_order;
>  		page_ext = page_ext_next(page_ext);
>  	}

This doesn't do what you're hoping it will.  It's going to set ->order to
new_order for the first N pages instead of every 1/N pages.

You'll need to do something like

		page_ext = lookup_page_ext(page + i);

or add a new page_ext_add(page_ext, 1 << new_order);