mm/shmem: return head page from find_lock_entry

Convert shmem_getpage_gfp() (the only remaining caller of
find_lock_entry()) to cope with a head page being returned instead of
the subpage for the index.

[willy@infradead.org: fix BUG()s]
  Link https://lore.kernel.org/linux-mm/20200912032042.GA6583@casper.infradead.org/

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: William Kucharski <william.kucharski@oracle.com>
Link: https://lkml.kernel.org/r/20200910183318.20139-8-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 9d282fe..5176009 100644 (file)
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -372,6 +372,15 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping,
                        mapping_gfp_mask(mapping));
 }
 
+/* Does this page contain this index? */
+static inline bool thp_contains(struct page *head, pgoff_t index)
+{
+       /* HugeTLBfs indexes the page cache in units of hpage_size */
+       if (PageHuge(head))
+               return head->index == index;
+       return page_index(head) == (index & ~(thp_nr_pages(head) - 1UL));
+}
+
 /*
  * Given the page we found in the page cache, return the page corresponding
  * to this index in the file

diff --git a/mm/filemap.c b/mm/filemap.c
index 9457d4f..b44346a 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1692,37 +1692,34 @@ out:
 }
 
 /**
- * find_lock_entry - locate, pin and lock a page cache entry
- * @mapping: the address_space to search
- * @offset: the page cache index
+ * 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 cache slot at @mapping & @offset.  If there is a
- * page cache page, it is returned locked and with an increased
- * refcount.
+ * 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.
  *
- * find_lock_entry() may sleep.
- *
- * Return: the found page or shadow entry, %NULL if nothing is found.
+ * 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 offset)
+struct page *find_lock_entry(struct address_space *mapping, pgoff_t index)
 {
        struct page *page;
 
 repeat:
-       page = find_get_entry(mapping, offset);
+       page = find_get_entry(mapping, index);
        if (page && !xa_is_value(page)) {
                lock_page(page);
                /* Has the page been truncated? */
-               if (unlikely(page_mapping(page) != mapping)) {
+               if (unlikely(page->mapping != mapping)) {
                        unlock_page(page);
                        put_page(page);
                        goto repeat;
                }
-               page = find_subpage(page, offset);
-               VM_BUG_ON_PAGE(page_to_pgoff(page) != offset, page);
+               VM_BUG_ON_PAGE(!thp_contains(page, index), page);
        }
        return page;
 }

diff --git a/mm/shmem.c b/mm/shmem.c
index d42c27e..6d4ddef 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1830,6 +1830,8 @@ repeat:
                return error;
        }
 
+       if (page)
+               hindex = page->index;
        if (page && sgp == SGP_WRITE)
                mark_page_accessed(page);
 
@@ -1840,11 +1842,10 @@ repeat:
                unlock_page(page);
                put_page(page);
                page = NULL;
+               hindex = index;
        }
-       if (page || sgp == SGP_READ) {
-               *pagep = page;
-               return 0;
-       }
+       if (page || sgp == SGP_READ)
+               goto out;
 
        /*
         * Fast cache lookup did not find it:
@@ -1969,14 +1970,13 @@ clear:
         * it now, lest undo on failure cancel our earlier guarantee.
         */
        if (sgp != SGP_WRITE && !PageUptodate(page)) {
-               struct page *head = compound_head(page);
                int i;
 
-               for (i = 0; i < compound_nr(head); i++) {
-                       clear_highpage(head + i);
-                       flush_dcache_page(head + i);
+               for (i = 0; i < compound_nr(page); i++) {
+                       clear_highpage(page + i);
+                       flush_dcache_page(page + i);
                }
-               SetPageUptodate(head);
+               SetPageUptodate(page);
        }
 
        /* Perhaps the file has been truncated since we checked */
@@ -1992,6 +1992,7 @@ clear:
                error = -EINVAL;
                goto unlock;
        }
+out:
        *pagep = page + index - hindex;
        return 0;