afs: Prepare for use of THPs

As a prelude to supporting transparent huge pages, use thp_size() and
similar rather than PAGE_SIZE/SHIFT.

Further, try and frame everything in terms of file positions and lengths
rather than page indices and numbers of pages.

Signed-off-by: David Howells <dhowells@redhat.com>
Tested-By: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/160588540227.3465195.4752143929716269062.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/161118155821.1232039.540445038028845740.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/161161051439.2537118.15577827510426326534.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/161340415869.1303470.6040191748634322355.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/161539559365.286939.18344613540296085269.stgit@warthog.procyon.org.uk/ # v4
Link: https://lore.kernel.org/r/161653815142.2770958.454490670311230206.stgit@warthog.procyon.org.uk/ # v5
Link: https://lore.kernel.org/r/161789098713.6155.16394227991842480300.stgit@warthog.procyon.org.uk/ # v6

fs/afs/dir.c

@@ -2083,6 +2083,6 @@ static void afs_dir_invalidatepage(struct page *page, unsigned int offset,
 		afs_stat_v(dvnode, n_inval);
 
 	/* we clean up only if the entire page is being invalidated */
-	if (offset == 0 && length == PAGE_SIZE)
+	if (offset == 0 && length == thp_size(page))
 		detach_page_private(page);
 }

fs/afs/file.c

@@ -329,8 +329,8 @@ static int afs_page_filler(struct key *key, struct page *page)
 	req->vnode		= vnode;
 	req->key		= key_get(key);
 	req->pos		= (loff_t)page->index << PAGE_SHIFT;
-	req->len		= PAGE_SIZE;
-	req->nr_pages		= 1;
+	req->len		= thp_size(page);
+	req->nr_pages		= thp_nr_pages(page);
 	req->done		= afs_file_read_done;
 	req->cleanup		= afs_file_read_cleanup;
 
@@ -574,8 +574,8 @@ undirty:
 	trace_afs_page_dirty(vnode, tracepoint_string("undirty"), page);
 	clear_page_dirty_for_io(page);
 full_invalidate:
-	detach_page_private(page);
 	trace_afs_page_dirty(vnode, tracepoint_string("inval"), page);
+	detach_page_private(page);
 }
 
 /*
@@ -620,8 +620,8 @@ static int afs_releasepage(struct page *page, gfp_t gfp_flags)
 #endif
 
 	if (PagePrivate(page)) {
-		detach_page_private(page);
 		trace_afs_page_dirty(vnode, tracepoint_string("rel"), page);
+		detach_page_private(page);
 	}
 
 	/* indicate that the page can be released */

fs/afs/internal.h

@@ -815,8 +815,6 @@ struct afs_operation {
 			loff_t	pos;
 			loff_t	size;
 			loff_t	i_size;
-			pgoff_t	first;		/* first page in mapping to deal with */
-			pgoff_t	last;		/* last page in mapping to deal with */
 			bool	laundering;	/* Laundering page, PG_writeback not set */
 		} store;
 		struct {