mm: change invalidatepage prototype to accept length

Currently there is no way to truncate partial page where the end
truncate point is not at the end of the page. This is because it was not
needed and the functionality was enough for file system truncate
operation to work properly. However more file systems now support punch
hole feature and it can benefit from mm supporting truncating page just
up to the certain point.

Specifically, with this functionality truncate_inode_pages_range() can
be changed so it supports truncating partial page at the end of the
range (currently it will BUG_ON() if 'end' is not at the end of the
page).

This commit changes the invalidatepage() address space operation
prototype to accept range to be invalidated and update all the instances
for it.

We also change the block_invalidatepage() in the same way and actually
make a use of the new length argument implementing range invalidation.

Actual file system implementations will follow except the file systems
where the changes are really simple and should not change the behaviour
in any way .Implementation for truncate_page_range() which will be able
to accept page unaligned ranges will follow as well.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>

1 files changed, 5 insertions, 3 deletions

diff --git a/fs/gfs2/aops.c b/fs/gfs2/aops.c
index 0bad69ed6336..db0d39f9fba4 100644
--- a/fs/gfs2/aops.c
+++ b/fs/gfs2/aops.c
@@ -110,7 +110,7 @@ static int gfs2_writepage_common(struct page *page,
         /* Is the page fully outside i_size? (truncate in progress) */
         offset = i_size & (PAGE_CACHE_SIZE-1);
         if (page->index > end_index || (page->index == end_index && !offset)) {
-                page->mapping->a_ops->invalidatepage(page, 0);
+                page->mapping->a_ops->invalidatepage(page, 0, PAGE_CACHE_SIZE);
                 goto out;
         }
         return 1;
@@ -299,7 +299,8 @@ static int gfs2_write_jdata_pagevec(struct address_space *mapping,
 
                 /* Is the page fully outside i_size? (truncate in progress) */
                 if (page->index > end_index || (page->index == end_index && !offset)) {
-                        page->mapping->a_ops->invalidatepage(page, 0);
+                        page->mapping->a_ops->invalidatepage(page, 0,
+                                                             PAGE_CACHE_SIZE);
                         unlock_page(page);
                         continue;
                 }
@@ -943,7 +944,8 @@ static void gfs2_discard(struct gfs2_sbd *sdp, struct buffer_head *bh)
         unlock_buffer(bh);
 }
 
-static void gfs2_invalidatepage(struct page *page, unsigned long offset)
+static void gfs2_invalidatepage(struct page *page, unsigned int offset,
+                                unsigned int length)
 {
         struct gfs2_sbd *sdp = GFS2_SB(page->mapping->host);
         struct buffer_head *bh, *head;