mm: add support for direct_IO to highmem pages

The patch "mm: add support for a filesystem to activate swap files and use
direct_IO for writing swap pages" added support for using direct_IO to
write swap pages but it is insufficient for highmem pages.

To support highmem pages, this patch kmaps() the page before calling the
direct_IO() handler.  As direct_IO deals with virtual addresses an
additional helper is necessary for get_kernel_pages() to lookup the struct
page for a kmap virtual address.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Eric B Munson <emunson@mgebm.net>
Cc: Eric Paris <eparis@redhat.com>
Cc: James Morris <jmorris@namei.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Christie <michaelc@cs.wisc.edu>
Cc: Neil Brown <neilb@suse.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Xiaotian Feng <dfeng@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/mm/page_io.c b/mm/page_io.c
index 4a379629e31f..78eee32ee486 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -205,7 +205,7 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
                 struct file *swap_file = sis->swap_file;
                 struct address_space *mapping = swap_file->f_mapping;
                 struct iovec iov = {
-                        .iov_base = page_address(page),
+                        .iov_base = kmap(page),
                         .iov_len  = PAGE_SIZE,
                 };
 
@@ -218,6 +218,7 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
                 ret = mapping->a_ops->direct_IO(KERNEL_WRITE,
                                                 &kiocb, &iov,
                                                 kiocb.ki_pos, 1);
+                kunmap(page);
                 if (ret == PAGE_SIZE) {
                         count_vm_event(PSWPOUT);
                         ret = 0;