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Old 02-13-2020, 10:25 AM   #1
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Cramming page metadata into struct page

I asked this same question on stack overflow (here), but haven't gotten any responses. Here is my question:

I am looking at the definition of
struct page
in the file linux/mm_types.h. My question is in regards to the comment at the top of the definition:
struct page {
	unsigned long flags;		/* Atomic flags, some possibly
					         * updated asynchronously */
	 * Five words (20/40 bytes) are available in this union.
	 * WARNING: bit 0 of the first word is used for PageTail(). That
	 * means the other users of this union MUST NOT use the bit to
	 * avoid collision and false-positive PageTail().
If I want to use these 20 bytes to store metadata about a page, how would I do so? Is there anything that I would need to check before overwriting those addresses, so that I don't corrupt any valid data that was supposed to be there?

Last edited by danielNJ; 02-13-2020 at 01:03 PM.


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