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Subject[PATCH v4 04/16] mm: Add FGP_ENTRY
Date
The functionality of find_lock_entry() and find_get_entry() can be
provided by pagecache_get_pages(), which lets us delete find_lock_entry()
and make find_get_entry() static.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
include/linux/pagemap.h | 1 +
mm/filemap.c | 44 ++++++++---------------------------------
mm/internal.h | 3 ---
mm/shmem.c | 3 ++-
mm/swap_state.c | 3 ++-
5 files changed, 13 insertions(+), 41 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index edb990f3b930..55e1bff1c4b9 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -313,6 +313,7 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping,
#define FGP_NOWAIT 0x00000020
#define FGP_FOR_MMAP 0x00000040
#define FGP_HEAD 0x00000080
+#define FGP_ENTRY 0x00000100

struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
int fgp_flags, gfp_t cache_gfp_mask);
diff --git a/mm/filemap.c b/mm/filemap.c
index bb6f2ae5a68c..01603f021740 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1662,7 +1662,7 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping,
}
EXPORT_SYMBOL(page_cache_prev_miss);

-/**
+/*
* find_get_entry - find and get a page cache entry
* @mapping: the address_space to search
* @index: The page cache index.
@@ -1675,7 +1675,7 @@ EXPORT_SYMBOL(page_cache_prev_miss);
*
* Return: The head page or shadow entry, %NULL if nothing is found.
*/
-struct page *find_get_entry(struct address_space *mapping, pgoff_t index)
+static struct page *find_get_entry(struct address_space *mapping, pgoff_t index)
{
XA_STATE(xas, &mapping->i_pages, index);
struct page *page;
@@ -1711,39 +1711,6 @@ struct page *find_get_entry(struct address_space *mapping, pgoff_t index)
return page;
}

-/**
- * find_lock_entry - Locate and lock a page cache entry.
- * @mapping: The address_space to search.
- * @index: The page cache index.
- *
- * Looks up the page at @mapping & @index. If there is a page in the
- * cache, the head page is returned locked and with an increased refcount.
- *
- * If the slot holds a shadow entry of a previously evicted page, or a
- * swap entry from shmem/tmpfs, it is returned.
- *
- * Context: May sleep.
- * Return: The head page or shadow entry, %NULL if nothing is found.
- */
-struct page *find_lock_entry(struct address_space *mapping, pgoff_t index)
-{
- struct page *page;
-
-repeat:
- page = find_get_entry(mapping, index);
- if (page && !xa_is_value(page)) {
- lock_page(page);
- /* Has the page been truncated? */
- if (unlikely(page->mapping != mapping)) {
- unlock_page(page);
- put_page(page);
- goto repeat;
- }
- VM_BUG_ON_PAGE(!thp_contains(page, index), page);
- }
- return page;
-}
-
/**
* pagecache_get_page - Find and get a reference to a page.
* @mapping: The address_space to search.
@@ -1759,6 +1726,8 @@ struct page *find_lock_entry(struct address_space *mapping, pgoff_t index)
* * %FGP_LOCK - The page is returned locked.
* * %FGP_HEAD - If the page is present and a THP, return the head page
* rather than the exact page specified by the index.
+ * * %FGP_ENTRY - If there is a shadow / swap / DAX entry, return it
+ * instead of allocating a new page to replace it.
* * %FGP_CREAT - If no page is present then a new page is allocated using
* @gfp_mask and added to the page cache and the VM's LRU list.
* The page is returned locked and with an increased refcount.
@@ -1783,8 +1752,11 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,

repeat:
page = find_get_entry(mapping, index);
- if (xa_is_value(page))
+ if (xa_is_value(page)) {
+ if (fgp_flags & FGP_ENTRY)
+ return page;
page = NULL;
+ }
if (!page)
goto no_page;

diff --git a/mm/internal.h b/mm/internal.h
index c43ccdddb0f6..93880d460e12 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -60,9 +60,6 @@ static inline void force_page_cache_readahead(struct address_space *mapping,
force_page_cache_ra(&ractl, &file->f_ra, nr_to_read);
}

-struct page *find_get_entry(struct address_space *mapping, pgoff_t index);
-struct page *find_lock_entry(struct address_space *mapping, pgoff_t index);
-
/**
* page_evictable - test whether a page is evictable
* @page: the page to test
diff --git a/mm/shmem.c b/mm/shmem.c
index 8076c171731c..c4feb05425f2 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1831,7 +1831,8 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
sbinfo = SHMEM_SB(inode->i_sb);
charge_mm = vma ? vma->vm_mm : current->mm;

- page = find_lock_entry(mapping, index);
+ page = pagecache_get_page(mapping, index,
+ FGP_ENTRY | FGP_HEAD | FGP_LOCK, 0);
if (xa_is_value(page)) {
error = shmem_swapin_page(inode, index, &page,
sgp, gfp, vma, fault_type);
diff --git a/mm/swap_state.c b/mm/swap_state.c
index d2161154d873..7cb4433edaa2 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -427,7 +427,8 @@ struct page *find_get_incore_page(struct address_space *mapping, pgoff_t index)
{
swp_entry_t swp;
struct swap_info_struct *si;
- struct page *page = find_get_entry(mapping, index);
+ struct page *page = pagecache_get_page(mapping, index,
+ FGP_ENTRY | FGP_HEAD, 0);

if (!page)
return page;
--
2.28.0
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