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Date: Wed, 13 Mar 2024 15:44:13 +0100
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Subject: Re: [PATCH v5 20/37] mm: fix non-compound multi-order memory
 accounting in __free_pages
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To: Suren Baghdasaryan <surenb@google.com>, akpm@linux-foundation.org
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References: <20240306182440.2003814-1-surenb@google.com>
 <20240306182440.2003814-21-surenb@google.com>
From: Vlastimil Babka <vbabka@suse.cz>
In-Reply-To: <20240306182440.2003814-21-surenb@google.com>
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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@suse.cz>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>

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