Re: [PATCH v15 05/21] mm/thp: move lru_add_page_tail func to huge_memory.c

[Kirill A. Shutemov]

On Tue, Jul 07, 2020 at 08:00:11PM +0800, Alex Shi wrote:
> 
> 
> å 2020/7/7 äå7:46, Alex Shi åé:
> >  
> > +static void lru_add_page_tail(struct page *page, struct page *page_tail,
> > +				struct lruvec *lruvec, struct list_head *list)
> > +{
> > +	VM_BUG_ON_PAGE(!PageHead(page), page);
> > +	VM_BUG_ON_PAGE(PageCompound(page_tail), page);
> > +	VM_BUG_ON_PAGE(PageLRU(page_tail), page);
> > +	lockdep_assert_held(&lruvec_pgdat(lruvec)->lru_lock);
> > +
> > +	if (!list)
> > +		SetPageLRU(page_tail);
> > +
> > +	if (likely(PageLRU(page)))
> > +		list_add_tail(&page_tail->lru, &page->lru);
> > +	else if (list) {
> > +		/* page reclaim is reclaiming a huge page */
> > +		get_page(page_tail);
> > +		list_add_tail(&page_tail->lru, list);
> > +	} else {
> > +		/*
> > +		 * Head page has not yet been counted, as an hpage,
> > +		 * so we must account for each subpage individually.
> > +		 *
> > +		 * Put page_tail on the list at the correct position
> > +		 * so they all end up in order.
> > +		 */
> > +		add_page_to_lru_list_tail(page_tail, lruvec,
> > +					  page_lru(page_tail));
> 
> 
> I missed some points for this function, since in the call chain:
> split_huge_page() to lru_add_page_tail, the head page's lru won't be
> set when !PageLRU(head). But the other page_tail are add to lru list here
> Is it ok for this situation?

It doesn't differ from the situation when some pages are isolated from
LRU. Tail page has become completely on its own after
__split_huge_page_tail() has completed, it's not tied to the head page.

-- 
 Kirill A. Shutemov