xfs: simplify xfs_vm_writepage

The writepage implementation in XFS still tries to deal with dirty but
unmapped buffers which used to caused by writes through shared mmaps.  Since
the introduction of ->page_mkwrite these can't happen anymore, so remove the
code dealing with them.

Note that the all_bh variable which causes us to start I/O on all buffers on
the pages was controlled by the count of unmapped buffers, which also
included those not actually dirty.  It's now unconditionally initialized to
0 but set to 1 for the case of small file size extensions.  It probably can
be removed entirely, but that's left for another patch.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

1 files changed, 45 insertions, 94 deletions

diff --git a/fs/xfs/linux-2.6/xfs_aops.c b/fs/xfs/linux-2.6/xfs_aops.c
index 7744a3b630e0..1776cdd944b5 100644
--- a/fs/xfs/linux-2.6/xfs_aops.c
+++ b/fs/xfs/linux-2.6/xfs_aops.c
@@ -85,18 +85,15 @@ void
 xfs_count_page_state(
         struct page             *page,
         int                     *delalloc,
-        int                     *unmapped,
         int                     *unwritten)
 {
         struct buffer_head      *bh, *head;
 
-        *delalloc = *unmapped = *unwritten = 0;
+        *delalloc = *unwritten = 0;
 
         bh = head = page_buffers(page);
         do {
-                if (buffer_uptodate(bh) && !buffer_mapped(bh))
-                        (*unmapped) = 1;
-                else if (buffer_unwritten(bh))
+                if (buffer_unwritten(bh))
                         (*unwritten) = 1;
                 else if (buffer_delay(bh))
                         (*delalloc) = 1;
@@ -607,31 +604,30 @@ xfs_map_at_offset(
 STATIC unsigned int
 xfs_probe_page(
         struct page             *page,
-        unsigned int            pg_offset,
-        int                     mapped)
+        unsigned int            pg_offset)
 {
+        struct buffer_head      *bh, *head;
         int                     ret = 0;
 
         if (PageWriteback(page))
                 return 0;
+        if (!PageDirty(page))
+                return 0;
+        if (!page->mapping)
+                return 0;
+        if (!page_has_buffers(page))
+                return 0;
 
-        if (page->mapping && PageDirty(page)) {
-                if (page_has_buffers(page)) {
-                        struct buffer_head      *bh, *head;
-
-                        bh = head = page_buffers(page);
-                        do {
-                                if (!buffer_uptodate(bh))
-                                        break;
-                                if (mapped != buffer_mapped(bh))
-                                        break;
-                                ret += bh->b_size;
-                                if (ret >= pg_offset)
-                                        break;
-                        } while ((bh = bh->b_this_page) != head);
-                } else
-                        ret = mapped ? 0 : PAGE_CACHE_SIZE;
-        }
+        bh = head = page_buffers(page);
+        do {
+                if (!buffer_uptodate(bh))
+                        break;
+                if (!buffer_mapped(bh))
+                        break;
+                ret += bh->b_size;
+                if (ret >= pg_offset)
+                        break;
+        } while ((bh = bh->b_this_page) != head);
 
         return ret;
 }
@@ -641,8 +637,7 @@ xfs_probe_cluster(
         struct inode            *inode,
         struct page             *startpage,
         struct buffer_head      *bh,
-        struct buffer_head      *head,
-        int                     mapped)
+        struct buffer_head      *head)
 {
         struct pagevec          pvec;
         pgoff_t                 tindex, tlast, tloff;
@@ -651,7 +646,7 @@ xfs_probe_cluster(
 
         /* First sum forwards in this page */
         do {
-                if (!buffer_uptodate(bh) || (mapped != buffer_mapped(bh)))
+                if (!buffer_uptodate(bh) || !buffer_mapped(bh))
                         return total;
                 total += bh->b_size;
         } while ((bh = bh->b_this_page) != head);
@@ -685,7 +680,7 @@ xfs_probe_cluster(
                                 pg_offset = PAGE_CACHE_SIZE;
 
                         if (page->index == tindex && trylock_page(page)) {
-                                pg_len = xfs_probe_page(page, pg_offset, mapped);
+                                pg_len = xfs_probe_page(page, pg_offset);
                                 unlock_page(page);
                         }
 
@@ -1021,18 +1016,12 @@ out_invalidate:
  * For delalloc space on the page we need to allocate space and flush it.
  * For unwritten space on the page we need to start the conversion to
  * regular allocated space.
- * For unmapped buffer heads on the page we should allocate space if the
- * page is uptodate.
  * For any other dirty buffer heads on the page we should flush them.
  *
  * If we detect that a transaction would be required to flush the page, we
  * have to check the process flags first, if we are already in a transaction
  * or disk I/O during allocations is off, we need to fail the writepage and
  * redirty the page.
- *
- * The bh->b_state's cannot know if any of the blocks or which block for that
- * matter are dirty due to mmap writes, and therefore bh uptodate is only
- * valid if the page itself isn't completely uptodate.
  */
 STATIC int
 xfs_vm_writepage(
@@ -1040,8 +1029,7 @@ xfs_vm_writepage(
         struct writeback_control *wbc)
 {
         struct inode            *inode = page->mapping->host;
-        int                     need_trans;
-        int                     delalloc, unmapped, unwritten;
+        int                     delalloc, unwritten;
         struct buffer_head      *bh, *head;
         struct xfs_bmbt_irec    imap;
         xfs_ioend_t             *ioend = NULL, *iohead = NULL;
@@ -1052,10 +1040,12 @@ xfs_vm_writepage(
         ssize_t                 size, len;
         int                     flags, err, imap_valid = 0, uptodate = 1;
         int                     count = 0;
-        int                     all_bh;
+        int                     all_bh = 0;
 
         trace_xfs_writepage(inode, page, 0);
 
+        ASSERT(page_has_buffers(page));
+
         /*
          * Refuse to write the page out if we are called from reclaim context.
          *
@@ -1072,29 +1062,15 @@ xfs_vm_writepage(
                 goto out_fail;
 
         /*
-         * We need a transaction if:
-         *  1. There are delalloc buffers on the page
-         *  2. The page is uptodate and we have unmapped buffers
-         *  3. The page is uptodate and we have no buffers
-         *  4. There are unwritten buffers on the page
-         */
-        if (!page_has_buffers(page)) {
-                unmapped = 1;
-                need_trans = 1;
-        } else {
-                xfs_count_page_state(page, &delalloc, &unmapped, &unwritten);
-                if (!PageUptodate(page))
-                        unmapped = 0;
-                need_trans = delalloc + unmapped + unwritten;
-        }
-
-        /*
-         * If we need a transaction and the process flags say
-         * we are already in a transaction, or no IO is allowed
-         * then mark the page dirty again and leave the page
-         * as is.
+         * We need a transaction if there are delalloc or unwritten buffers
+         * on the page.
+         *
+         * If we need a transaction and the process flags say we are already
+         * in a transaction, or no IO is allowed then mark the page dirty
+         * again and leave the page as is.
          */
-        if (current_test_flags(PF_FSTRANS) && need_trans)
+        xfs_count_page_state(page, &delalloc, &unwritten);
+        if ((current->flags & PF_FSTRANS) && (delalloc || unwritten))
                 goto out_fail;
 
         /*
@@ -1117,7 +1093,8 @@ xfs_vm_writepage(
         }
 
         end_offset = min_t(unsigned long long,
-                        (xfs_off_t)(page->index + 1) << PAGE_CACHE_SHIFT, offset);
+                        (xfs_off_t)(page->index + 1) << PAGE_CACHE_SHIFT,
+                        offset);
         len = 1 << inode->i_blkbits;
 
         bh = head = page_buffers(page);
@@ -1125,8 +1102,6 @@ xfs_vm_writepage(
         flags = BMAPI_READ;
         type = IO_NEW;
 
-        all_bh = unmapped;
-
         do {
                 if (offset >= end_offset)
                         break;
@@ -1146,19 +1121,7 @@ xfs_vm_writepage(
                 if (imap_valid)
                         imap_valid = xfs_imap_valid(inode, &imap, offset);
 
-                /*
-                 * First case, map an unwritten extent and prepare for
-                 * extent state conversion transaction on completion.
-                 *
-                 * Second case, allocate space for a delalloc buffer.
-                 * We can return EAGAIN here in the release page case.
-                 *
-                 * Third case, an unmapped buffer was found, and we are
-                 * in a path where we need to write the whole page out.
-                 */
-                if (buffer_unwritten(bh) || buffer_delay(bh) ||
-                    ((buffer_uptodate(bh) || PageUptodate(page)) &&
-                     !buffer_mapped(bh))) {
+                if (buffer_unwritten(bh) || buffer_delay(bh)) {
                         int new_ioend = 0;
 
                         /*
@@ -1177,14 +1140,11 @@ xfs_vm_writepage(
                                 if (wbc->sync_mode == WB_SYNC_NONE &&
                                     wbc->nonblocking)
                                         flags |= BMAPI_TRYLOCK;
-                        } else {
-                                type = IO_NEW;
-                                flags = BMAPI_WRITE | BMAPI_MMAP;
                         }
 
                         if (!imap_valid) {
                                 /*
-                                 * if we didn't have a valid mapping then we
+                                 * If we didn't have a valid mapping then we
                                  * need to ensure that we put the new mapping
                                  * in a new ioend structure. This needs to be
                                  * done to ensure that the ioends correctly
@@ -1192,14 +1152,7 @@ xfs_vm_writepage(
                                  * for unwritten extent conversion.
                                  */
                                 new_ioend = 1;
-                                if (type == IO_NEW) {
-                                        size = xfs_probe_cluster(inode,
-                                                        page, bh, head, 0);
-                                } else {
-                                        size = len;
-                                }
-
-                                err = xfs_map_blocks(inode, offset, size,
+                                err = xfs_map_blocks(inode, offset, len,
                                                 &imap, flags);
                                 if (err)
                                         goto error;
@@ -1220,8 +1173,7 @@ xfs_vm_writepage(
                          */
                         if (!imap_valid || flags != BMAPI_READ) {
                                 flags = BMAPI_READ;
-                                size = xfs_probe_cluster(inode, page, bh,
-                                                                head, 1);
+                                size = xfs_probe_cluster(inode, page, bh, head);
                                 err = xfs_map_blocks(inode, offset, size,
                                                 &imap, flags);
                                 if (err)
@@ -1240,7 +1192,6 @@ xfs_vm_writepage(
                          */
                         type = IO_NEW;
                         if (trylock_buffer(bh)) {
-                                ASSERT(buffer_mapped(bh));
                                 if (imap_valid)
                                         all_bh = 1;
                                 xfs_add_to_ioend(inode, bh, offset, type,
@@ -1250,6 +1201,7 @@ xfs_vm_writepage(
                                 imap_valid = 0;
                         }
                 } else if (PageUptodate(page)) {
+                        ASSERT(buffer_mapped(bh));
                         imap_valid = 0;
                 }
 
@@ -1291,8 +1243,7 @@ error:
         if (iohead)
                 xfs_cancel_ioend(iohead);
 
-        if (!unmapped)
-                xfs_aops_discard_page(page);
+        xfs_aops_discard_page(page);
         ClearPageUptodate(page);
         unlock_page(page);
         return err;
@@ -1324,11 +1275,11 @@ xfs_vm_releasepage(
         struct page             *page,
         gfp_t                   gfp_mask)
 {
-        int                     delalloc, unmapped, unwritten;
+        int                     delalloc, unwritten;
 
         trace_xfs_releasepage(page->mapping->host, page, 0);
 
-        xfs_count_page_state(page, &delalloc, &unmapped, &unwritten);
+        xfs_count_page_state(page, &delalloc, &unwritten);
 
         if (WARN_ON(delalloc))
                 return 0;