On 12/16/2017 08:44 AM, Matthew Wilcox wrote:
> From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
>
> Be really explicit about what bits / bytes are reserved for users that
> want to store extra information about the pages they allocate.
>
> Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
> ---
> include/linux/mm_types.h | 23 ++++++++++++++++++++++-
> 1 file changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 1a3ba1f1605d..a517d210f177 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -31,7 +31,28 @@ struct hmm;
> * it to keep track of whatever it is we are using the page for at the
> * moment. Note that we have no way to track which tasks are using
> * a page, though if it is a pagecache page, rmap structures can tell us
> - * who is mapping it.
> + * who is mapping it. If you allocate the page using alloc_pages(), you
> + * can use some of the space in struct page for your own purposes.
> + *
> + * Pages that were once in the page cache may be found under the RCU lock
> + * even after they have been recycled to a different purpose. The page cache
> + * will read and writes some of the fields in struct page to lock the page,
"will read and writes" seems awkward to me.
Can that be:
* reads and writes
> + * then check that it's still in the page cache. It is vital that all users
> + * of struct page:
ta.
--
~Randy
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