[PATCH v14 126/138] mm/filemap: Return only head pages from find_get_entries

Matthew Wilcox (Oracle)
2021-07-15T05:19:53Z

All callers now expect head (and base) pages, and can handle multiple
head pages in a single batch, so make find_get_entries() behave that way.
Also take the opportunity to make it use the pagevec infrastructure
instead of open-coding how pvecs behave. This has the side-effect of
being able to append to a pagevec with existing contents, although we
don't make use of that functionality anywhere yet.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
---
include/linux/pagemap.h | 2 --
mm/filemap.c | 40 ++++++++++------------------------------
mm/internal.h | 2 ++
3 files changed, 12 insertions(+), 32 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 842d130fd6d3..bf8e978a48f2 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -502,8 +502,6 @@ static inline struct page *find_subpage(struct page *head, pgoff_t index)
return head + (index & (thp_nr_pages(head) - 1));
}

-unsigned find_get_entries(struct address_space *mapping, pgoff_t start,
- pgoff_t end, struct pagevec *pvec, pgoff_t *indices);
unsigned find_get_pages_range(struct address_space *mapping, pgoff_t *start,
pgoff_t end, unsigned int nr_pages,
struct page **pages);
diff --git a/mm/filemap.c b/mm/filemap.c
index 1c0c2663c57d..20434d7bdad8 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1955,49 +1955,29 @@ static inline struct folio *find_get_entry(struct xa_state *xas, pgoff_t max,
* the mapping. The entries are placed in @pvec. find_get_entries()
* takes a reference on any actual pages it returns.
*
- * The search returns a group of mapping-contiguous page cache entries
- * with ascending indexes. There may be holes in the indices due to
- * not-present pages.
+ * The entries have ascending indexes. The indices may not be consecutive
+ * due to not-present entries or THPs.
*
* Any shadow entries of evicted pages, or swap entries from
* shmem/tmpfs, are included in the returned array.
*
- * If it finds a Transparent Huge Page, head or tail, find_get_entries()
- * stops at that page: the caller is likely to have a better way to handle
- * the compound page as a whole, and then skip its extent, than repeatedly
- * calling find_get_entries() to return all its tails.
- *
- * Return: the number of pages and shadow entries which were found.
+ * Return: The number of entries which were found.
*/
unsigned find_get_entries(struct address_space *mapping, pgoff_t start,
pgoff_t end, struct pagevec *pvec, pgoff_t *indices)
{
XA_STATE(xas, &mapping->i_pages, start);
- struct page *page;
- unsigned int ret = 0;
- unsigned nr_entries = PAGEVEC_SIZE;
+ struct folio *folio;

rcu_read_lock();
- while ((page = &find_get_entry(&xas, end, XA_PRESENT)->page)) {
- /*
- * Terminate early on finding a THP, to allow the caller to
- * handle it all at once; but continue if this is hugetlbfs.
- */
- if (!xa_is_value(page) && PageTransHuge(page) &&
- !PageHuge(page)) {
- page = find_subpage(page, xas.xa_index);
- nr_entries = ret + 1;
- }
-
- indices[ret] = xas.xa_index;
- pvec->pages[ret] = page;
- if (++ret == nr_entries)
+ while ((folio = find_get_entry(&xas, end, XA_PRESENT)) != NULL) {
+ indices[pvec->nr] = xas.xa_index;
+ if (!pagevec_add(pvec, &folio->page))
break;
}
rcu_read_unlock();

- pvec->nr = ret;
- return ret;
+ return pagevec_count(pvec);
}

/**
@@ -2016,8 +1996,8 @@ unsigned find_get_entries(struct address_space *mapping, pgoff_t start,
* not returned.
*
* The entries have ascending indexes. The indices may not be consecutive
- * due to not-present entries, THP pages, pages which could not be locked
- * or pages under writeback.
+ * due to not-present entries, THPs, pages which could not be locked or
+ * pages under writeback.
*
* Return: The number of entries which were found.
*/
diff --git a/mm/internal.h b/mm/internal.h
index 3c0c807eddc6..3e32064df18d 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -70,6 +70,8 @@ static inline void force_page_cache_readahead(struct address_space *mapping,

unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
pgoff_t end, struct pagevec *pvec, pgoff_t *indices);
+unsigned find_get_entries(struct address_space *mapping, pgoff_t start,
+ pgoff_t end, struct pagevec *pvec, pgoff_t *indices);
bool truncate_inode_partial_page(struct page *page, loff_t start, loff_t end);

/**
--
2.30.2