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SubjectRe: [PATCH 06/10] ksm: identify PageKsm pages
On Fri, Jul 17, 2009 at 08:30:46PM +0300, Izik Eidus wrote:
> +static inline int PageKsm(struct page *page)
> +{
> + return ((unsigned long)page->mapping == PAGE_MAPPING_ANON);
> +}

I'm unconvinced it's sane to have PageAnon return 1 on Ksm pages.

The above will also have short lifetime so not sure it's worth it,
if we want to swap we'll have to move to something that to:

PageExternal()
{
return (unsigned long)page->mapping & PAGE_MAPPING_EXTERNAL != 0;
}
> +static inline void page_add_ksm_rmap(struct page *page)
> +{
> + if (atomic_inc_and_test(&page->_mapcount)) {
> + page->mapping = (void *) PAGE_MAPPING_ANON;
> + __inc_zone_page_state(page, NR_ANON_PAGES);
> + }
> +}

Is it correct to account them as anon pages?

> - if (PageAnon(old_page)) {
> + if (PageAnon(old_page) && !PageKsm(old_page)) {
> if (!trylock_page(old_page)) {
> page_cache_get(old_page);
> pte_unmap_unlock(page_table, ptl);

What exactly does it buy to have PageAnon return 1 on ksm pages,
besides requiring the above additional check (that if we stick to the
above code, I would find safer to move inside reuse_swap_page).


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