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From: Matthew Wilcox <>
To: Yunsheng Lin <>
Subject: Re: [PATCH net] page_pool: mask the page->signature before the checking
Date: Thu, 5 Aug 2021 02:50:02 +0100	[thread overview]
Message-ID: <YQtDynWsDxZ/> (raw)
In-Reply-To: <>

On Thu, Aug 05, 2021 at 09:06:57AM +0800, Yunsheng Lin wrote:
> As mentioned in commit c07aea3ef4d4 ("mm: add a signature
> in struct page"):
> "The page->signature field is aliased to page-> and
> page->compound_head."
> And as the comment in page_is_pfmemalloc():
> " has bit 1 set if the page is allocated from the
> pfmemalloc reserves. Callers may simply overwrite it if they
> do not need to preserve that information."
> The page->signature is or’ed with PP_SIGNATURE when a page is
> allocated in page pool, see __page_pool_alloc_pages_slow(),
> and page->signature is checked directly with PP_SIGNATURE in
> page_pool_return_skb_page(), which might cause resoure leaking
> problem for a page from page pool if bit 1 of is set for
> a pfmemalloc page.
> As bit 0 is page->compound_head, So mask both bit 0 and 1 before
> the checking in page_pool_return_skb_page().

No, you don't understand.  We *want* the check to fail if we were low
on memory so we return the emergency allocation.

  reply	other threads:[~2021-08-05  1:51 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-05  1:06 Yunsheng Lin
2021-08-05  1:50 ` Matthew Wilcox [this message]
2021-08-05  2:14   ` Yunsheng Lin
2021-08-05  8:54     ` Ilias Apalodimas
2021-08-05  9:31       ` Yunsheng Lin
2021-08-05 14:47         ` Ilias Apalodimas

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