linux-kernel - Re: [PATCH v5 20/37] mm: fix non-compound multi-order memory accounting in __free

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Message-ID: <76c84f17-8b99-4f68-a6ac-a0db22f5ace3@suse.cz>
Date: Wed, 13 Mar 2024 15:44:13 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org
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Subject: Re: [PATCH v5 20/37] mm: fix non-compound multi-order memory
 accounting in __free_pages



On 3/6/24 19:24, Suren Baghdasaryan wrote:
> When a non-compound multi-order page is freed, it is possible that a
> speculative reference keeps the page pinned. In this case we free all
> pages except for the first page, which will be freed later by the last
> put_page(). However put_page() ignores the order of the page being freed,
> treating it as a 0-order page. This creates a memory accounting imbalance
> because the pages freed in __free_pages() do not have their own alloc_tag
> and their memory was accounted to the first page. To fix this the first
> page should adjust its allocation size counter when "tail" pages are freed.
> 
> Reported-by: Vlastimil Babka <vbabka@...e.cz>
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>