NFS: Allow redirtying of a completed unstable write.

Currently, if an unstable write completes, we cannot redirty the page in
order to reflect a new change in the page data until after we've sent a
COMMIT request.

This patch allows a page rewrite to proceed without the unnecessary COMMIT
step, putting it immediately back onto the dirty page list, undoing the
VM unstable write accounting, and removing the NFS_PAGE_TAG_COMMIT tag from
the NFS radix tree.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

2 files changed, 38 insertions, 36 deletions

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 04f51e52e184..feca8c648766 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -242,12 +242,9 @@ static int nfs_page_async_flush(struct nfs_pageio_descriptor *pgio,
                         return ret;
                 spin_lock(&inode->i_lock);
         }
-        if (test_bit(PG_NEED_COMMIT, &req->wb_flags)) {
-                /* This request is marked for commit */
+        if (test_bit(PG_CLEAN, &req->wb_flags)) {
                 spin_unlock(&inode->i_lock);
-                nfs_clear_page_tag_locked(req);
-                nfs_pageio_complete(pgio);
-                return 0;
+                BUG();
         }
         if (nfs_set_page_writeback(page) != 0) {
                 spin_unlock(&inode->i_lock);
@@ -391,19 +388,6 @@ nfs_mark_request_dirty(struct nfs_page *req)
         __set_page_dirty_nobuffers(req->wb_page);
 }
 
-/*
- * Check if a request is dirty
- */
-static inline int
-nfs_dirty_request(struct nfs_page *req)
-{
-        struct page *page = req->wb_page;
-
-        if (page == NULL || test_bit(PG_NEED_COMMIT, &req->wb_flags))
-                return 0;
-        return !PageWriteback(page);
-}
-
 #if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
 /*
  * Add a request to the inode's commit list.
@@ -416,7 +400,7 @@ nfs_mark_request_commit(struct nfs_page *req)
 
         spin_lock(&inode->i_lock);
         nfsi->ncommit++;
-        set_bit(PG_NEED_COMMIT, &(req)->wb_flags);
+        set_bit(PG_CLEAN, &(req)->wb_flags);
         radix_tree_tag_set(&nfsi->nfs_page_tree,
                         req->wb_index,
                         NFS_PAGE_TAG_COMMIT);
@@ -426,6 +410,19 @@ nfs_mark_request_commit(struct nfs_page *req)
         __mark_inode_dirty(inode, I_DIRTY_DATASYNC);
 }
 
+static int
+nfs_clear_request_commit(struct nfs_page *req)
+{
+        struct page *page = req->wb_page;
+
+        if (test_and_clear_bit(PG_CLEAN, &(req)->wb_flags)) {
+                dec_zone_page_state(page, NR_UNSTABLE_NFS);
+                dec_bdi_stat(page->mapping->backing_dev_info, BDI_RECLAIMABLE);
+                return 1;
+        }
+        return 0;
+}
+
 static inline
 int nfs_write_need_commit(struct nfs_write_data *data)
 {
@@ -435,7 +432,7 @@ int nfs_write_need_commit(struct nfs_write_data *data)
 static inline
 int nfs_reschedule_unstable_write(struct nfs_page *req)
 {
-        if (test_bit(PG_NEED_COMMIT, &req->wb_flags)) {
+        if (test_and_clear_bit(PG_NEED_COMMIT, &req->wb_flags)) {
                 nfs_mark_request_commit(req);
                 return 1;
         }
@@ -451,6 +448,12 @@ nfs_mark_request_commit(struct nfs_page *req)
 {
 }
 
+static inline int
+nfs_clear_request_commit(struct nfs_page *req)
+{
+        return 0;
+}
+
 static inline
 int nfs_write_need_commit(struct nfs_write_data *data)
 {
@@ -508,11 +511,8 @@ static void nfs_cancel_commit_list(struct list_head *head)
 
         while(!list_empty(head)) {
                 req = nfs_list_entry(head->next);
-                dec_zone_page_state(req->wb_page, NR_UNSTABLE_NFS);
-                dec_bdi_stat(req->wb_page->mapping->backing_dev_info,
-                                BDI_RECLAIMABLE);
                 nfs_list_remove_request(req);
-                clear_bit(PG_NEED_COMMIT, &(req)->wb_flags);
+                nfs_clear_request_commit(req);
                 nfs_inode_remove_request(req);
                 nfs_unlock_request(req);
         }
@@ -584,8 +584,7 @@ static struct nfs_page *nfs_try_to_update_request(struct inode *inode,
                  * Note: nfs_flush_incompatible() will already
                  * have flushed out requests having wrong owners.
                  */
-                if (!nfs_dirty_request(req)
-                    || offset > rqend
+                if (offset > rqend
                     || end < req->wb_offset)
                         goto out_flushme;
 
@@ -601,6 +600,10 @@ static struct nfs_page *nfs_try_to_update_request(struct inode *inode,
                 spin_lock(&inode->i_lock);
         }
 
+        if (nfs_clear_request_commit(req))
+                radix_tree_tag_clear(&NFS_I(inode)->nfs_page_tree,
+                                req->wb_index, NFS_PAGE_TAG_COMMIT);
+
         /* Okay, the request matches. Update the region */
         if (offset < req->wb_offset) {
                 req->wb_offset = offset;
@@ -682,8 +685,7 @@ int nfs_flush_incompatible(struct file *file, struct page *page)
                 req = nfs_page_find_request(page);
                 if (req == NULL)
                         return 0;
-                do_flush = req->wb_page != page || req->wb_context != ctx
-                        || !nfs_dirty_request(req);
+                do_flush = req->wb_page != page || req->wb_context != ctx;
                 nfs_release_request(req);
                 if (!do_flush)
                         return 0;
@@ -1288,10 +1290,7 @@ static void nfs_commit_release(void *calldata)
         while (!list_empty(&data->pages)) {
                 req = nfs_list_entry(data->pages.next);
                 nfs_list_remove_request(req);
-                clear_bit(PG_NEED_COMMIT, &(req)->wb_flags);
-                dec_zone_page_state(req->wb_page, NR_UNSTABLE_NFS);
-                dec_bdi_stat(req->wb_page->mapping->backing_dev_info,
-                                BDI_RECLAIMABLE);
+                nfs_clear_request_commit(req);
 
                 dprintk("NFS:       commit (%s/%lld %d@%lld)",
                         req->wb_context->path.dentry->d_inode->i_sb->s_id,
@@ -1467,7 +1466,7 @@ int nfs_wb_page_cancel(struct inode *inode, struct page *page)
                 req = nfs_page_find_request(page);
                 if (req == NULL)
                         goto out;
-                if (test_bit(PG_NEED_COMMIT, &req->wb_flags)) {
+                if (test_bit(PG_CLEAN, &req->wb_flags)) {
                         nfs_release_request(req);
                         break;
                 }
diff --git a/include/linux/nfs_page.h b/include/linux/nfs_page.h
index a1676e19e491..3c60685d972b 100644
--- a/include/linux/nfs_page.h
+++ b/include/linux/nfs_page.h
@@ -27,9 +27,12 @@
 /*
  * Valid flags for a dirty buffer
  */
-#define PG_BUSY                 0
-#define PG_NEED_COMMIT          1
-#define PG_NEED_RESCHED         2
+enum {
+        PG_BUSY = 0,
+        PG_CLEAN,
+        PG_NEED_COMMIT,
+        PG_NEED_RESCHED,
+};
 
 struct nfs_inode;
 struct nfs_page {