mm/filemap: use page_cache_sync_ra() to kick off read-ahead

Rather than use the page_cache_sync_readahead() helper, define our own
ractl and use page_cache_sync_ra() directly.  In preparation for needing
to modify ractl inside filemap_get_pages().

No functional changes in this patch.

Link: https://lkml.kernel.org/r/20241220154831.1086649-3-axboe@kernel.dk
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Brian Foster <bfoster@redhat.com>
Cc: Chris Mason <clm@meta.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: axboe

mm/filemap.c

@@ -2499,7 +2499,6 @@ static int filemap_get_pages(struct kiocb *iocb, size_t count,
 {
 	struct file *filp = iocb->ki_filp;
 	struct address_space *mapping = filp->f_mapping;
-	struct file_ra_state *ra = &filp->f_ra;
 	pgoff_t index = iocb->ki_pos >> PAGE_SHIFT;
 	pgoff_t last_index;
 	struct folio *folio;
@@ -2514,12 +2513,13 @@ static int filemap_get_pages(struct kiocb *iocb, size_t count,
 
 	filemap_get_read_batch(mapping, index, last_index - 1, fbatch);
 	if (!folio_batch_count(fbatch)) {
+		DEFINE_READAHEAD(ractl, filp, &filp->f_ra, mapping, index);
+
 		if (iocb->ki_flags & IOCB_NOIO)
 			return -EAGAIN;
 		if (iocb->ki_flags & IOCB_NOWAIT)
 			flags = memalloc_noio_save();
-		page_cache_sync_readahead(mapping, ra, filp, index,
-				last_index - index);
+		page_cache_sync_ra(&ractl, last_index - index);
 		if (iocb->ki_flags & IOCB_NOWAIT)
 			memalloc_noio_restore(flags);
 		filemap_get_read_batch(mapping, index, last_index - 1, fbatch);