mm/filemap: add helper for finding pages

There is a lot of common code in find_get_entries(),
find_get_pages_range() and find_get_pages_range_tag().  Factor out
find_get_entry() which simplifies all three functions.

[willy@infradead.org: remove VM_BUG_ON_PAGE()]
Link: https://lkml.kernel.org/r/20201124041507.28996-2-willy@infradead.orgLink:
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/filemap.c b/mm/filemap.c
index 087308c..2144385 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1825,6 +1825,42 @@ no_page:
 }
 EXPORT_SYMBOL(pagecache_get_page);
 
+static inline struct page *find_get_entry(struct xa_state *xas, pgoff_t max,
+               xa_mark_t mark)
+{
+       struct page *page;
+
+retry:
+       if (mark == XA_PRESENT)
+               page = xas_find(xas, max);
+       else
+               page = xas_find_marked(xas, max, mark);
+
+       if (xas_retry(xas, page))
+               goto retry;
+       /*
+        * A shadow entry of a recently evicted page, a swap
+        * entry from shmem/tmpfs or a DAX entry.  Return it
+        * without attempting to raise page count.
+        */
+       if (!page || xa_is_value(page))
+               return page;
+
+       if (!page_cache_get_speculative(page))
+               goto reset;
+
+       /* Has the page moved or been split? */
+       if (unlikely(page != xas_reload(xas))) {
+               put_page(page);
+               goto reset;
+       }
+
+       return page;
+reset:
+       xas_reset(xas);
+       goto retry;
+}
+
 /**
  * find_get_entries - gang pagecache lookup
  * @mapping:   The address_space to search
@@ -1864,42 +1900,21 @@ unsigned find_get_entries(struct address_space *mapping,
                return 0;
 
        rcu_read_lock();
-       xas_for_each(&xas, page, ULONG_MAX) {
-               if (xas_retry(&xas, page))
-                       continue;
-               /*
-                * A shadow entry of a recently evicted page, a swap
-                * entry from shmem/tmpfs or a DAX entry.  Return it
-                * without attempting to raise page count.
-                */
-               if (xa_is_value(page))
-                       goto export;
-
-               if (!page_cache_get_speculative(page))
-                       goto retry;
-
-               /* Has the page moved or been split? */
-               if (unlikely(page != xas_reload(&xas)))
-                       goto put_page;
-
+       while ((page = find_get_entry(&xas, ULONG_MAX, XA_PRESENT))) {
                /*
                 * Terminate early on finding a THP, to allow the caller to
                 * handle it all at once; but continue if this is hugetlbfs.
                 */
-               if (PageTransHuge(page) && !PageHuge(page)) {
+               if (!xa_is_value(page) && PageTransHuge(page) &&
+                               !PageHuge(page)) {
                        page = find_subpage(page, xas.xa_index);
                        nr_entries = ret + 1;
                }
-export:
+
                indices[ret] = xas.xa_index;
                entries[ret] = page;
                if (++ret == nr_entries)
                        break;
-               continue;
-put_page:
-               put_page(page);
-retry:
-               xas_reset(&xas);
        }
        rcu_read_unlock();
        return ret;
@@ -1938,30 +1953,16 @@ unsigned find_get_pages_range(struct address_space *mapping, pgoff_t *start,
                return 0;
 
        rcu_read_lock();
-       xas_for_each(&xas, page, end) {
-               if (xas_retry(&xas, page))
-                       continue;
+       while ((page = find_get_entry(&xas, end, XA_PRESENT))) {
                /* Skip over shadow, swap and DAX entries */
                if (xa_is_value(page))
                        continue;
 
-               if (!page_cache_get_speculative(page))
-                       goto retry;
-
-               /* Has the page moved or been split? */
-               if (unlikely(page != xas_reload(&xas)))
-                       goto put_page;
-
                pages[ret] = find_subpage(page, xas.xa_index);
                if (++ret == nr_pages) {
                        *start = xas.xa_index + 1;
                        goto out;
                }
-               continue;
-put_page:
-               put_page(page);
-retry:
-               xas_reset(&xas);
        }
 
        /*
@@ -2061,9 +2062,7 @@ unsigned find_get_pages_range_tag(struct address_space *mapping, pgoff_t *index,
                return 0;
 
        rcu_read_lock();
-       xas_for_each_marked(&xas, page, end, tag) {
-               if (xas_retry(&xas, page))
-                       continue;
+       while ((page = find_get_entry(&xas, end, tag))) {
                /*
                 * Shadow entries should never be tagged, but this iteration
                 * is lockless so there is a window for page reclaim to evict
@@ -2072,23 +2071,11 @@ unsigned find_get_pages_range_tag(struct address_space *mapping, pgoff_t *index,
                if (xa_is_value(page))
                        continue;
 
-               if (!page_cache_get_speculative(page))
-                       goto retry;
-
-               /* Has the page moved or been split? */
-               if (unlikely(page != xas_reload(&xas)))
-                       goto put_page;
-
                pages[ret] = page;
                if (++ret == nr_pages) {
                        *index = page->index + thp_nr_pages(page);
                        goto out;
                }
-               continue;
-put_page:
-               put_page(page);
-retry:
-               xas_reset(&xas);
        }
 
        /*