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SubjectRe: [PATCH v3 18/25] mm: Allow large pages to be added to the page cache
On Wed, Apr 29, 2020 at 06:36:50AM -0700, Matthew Wilcox wrote:
> @@ -886,7 +906,7 @@ static int __add_to_page_cache_locked(struct page *page,
> /* Leave page->index set: truncation relies upon it */
> if (!huge)
> mem_cgroup_cancel_charge(page, memcg, false);
> - put_page(page);
> + page_ref_sub(page, nr);
> return xas_error(&xas);
> }
> ALLOW_ERROR_INJECTION(__add_to_page_cache_locked, ERRNO);

This is wrong. page_ref_sub() will not call __put_page() if the refcount
gets to zero. What do people prefer?

- put_page(page);

(a)
+ put_thp(page);

(b)
+ put_page_nr(page, nr);

(c)
+ if (page_ref_sub_return(page, nr) == 0)
+ __put_page(page);

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