linux-kernel - Re: [PATCH 1/3] mm, page_owner: record page owner for each subpage

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Message-ID: <20190816140430.aoya6k7qxxrls72h@box>
Date:   Fri, 16 Aug 2019 17:04:30 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Michal Hocko <mhocko@...nel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH 1/3] mm, page_owner: record page owner for each subpage

On Fri, Aug 16, 2019 at 12:13:59PM +0200, Vlastimil Babka wrote:
> Currently, page owner info is only recorded for the first page of a high-order
> allocation, and copied to tail pages in the event of a split page. With the
> plan to keep previous owner info after freeing the page, it would be benefical
> to record page owner for each subpage upon allocation. This increases the
> overhead for high orders, but that should be acceptable for a debugging option.
> 
> The order stored for each subpage is the order of the whole allocation. This
> makes it possible to calculate the "head" pfn and to recognize "tail" pages
> (quoted because not all high-order allocations are compound pages with true
> head and tail pages). When reading the page_owner debugfs file, keep skipping
> the "tail" pages so that stats gathered by existing scripts don't get inflated.
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>

Hm. That's all reasonable, but I have a question: do you see how page
owner thing works for THP now?

I don't see anything in split_huge_page() path (do not confuse it with
split_page() path) that would copy the information to tail pages. Do you?

-- 
 Kirill A. Shutemov