Re: [Lhms-devel] new memory hotremoval patch

[IWAMOTO Toshihiro]

At Wed, 30 Jun 2004 17:11:11 -0700,
Dave Hansen wrote:
> 
> On Wed, 2004-06-30 at 04:17, IWAMOTO Toshihiro wrote:
> > Due to struct page changes, page->mapping == NULL predicate can no
> > longer be used for detecting cancellation of an anonymous page
> > remapping operation.  So the PG_again bit is being used again.
> > It may be still possible to kill the PG_again bit, but the priority is
> > rather low.
> 
> But, you reintroduced it everywhere, including file-backed pages, not
> just for anonymous pages?  Why was this necessary?

Which PG_again check are you talking about?
I think BUG_ON()s in file backed page codes should be kept for now.

For swap pages, one possibility to reserve a special swap entry
constant (SWAP_AGAIN) and check page->private instead of PageAgain
check, but I'm not sure if this is a good idea.

#define	SWAP_AGAIN	~0UL

...

static int do_swap_page(struct mm_struct * mm,
        struct vm_area_struct * vma, unsigned long address,
        pte_t *page_table, pmd_t *pmd, pte_t orig_pte, int write_access)
{
...
again:
        page = lookup_swap_cache(entry);
...
        mark_page_accessed(page);
        lock_page(page);
        if (page->private == SWAP_AGAIN) {
		...
		goto again;
	}

--
IWAMOTO Toshihiro
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