NFS: Optimise append writes with holes
If a file is being extended, and we're creating a hole, we might as well
declare the entire page to be up to date.
This patch significantly improves the write performance for sparse files
in the case where lseek(SEEK_END) is used to append several non-contiguous
writes at intervals of < PAGE_SIZE.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 7c73f06..7ac89a8 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -344,6 +344,26 @@
unsigned offset = pos & (PAGE_CACHE_SIZE - 1);
int status;
+ /*
+ * Zero any uninitialised parts of the page, and then mark the page
+ * as up to date if it turns out that we're extending the file.
+ */
+ if (!PageUptodate(page)) {
+ unsigned pglen = nfs_page_length(page);
+ unsigned end = offset + len;
+
+ if (pglen == 0) {
+ zero_user_segments(page, 0, offset,
+ end, PAGE_CACHE_SIZE);
+ SetPageUptodate(page);
+ } else if (end >= pglen) {
+ zero_user_segment(page, end, PAGE_CACHE_SIZE);
+ if (offset == 0)
+ SetPageUptodate(page);
+ } else
+ zero_user_segment(page, pglen, PAGE_CACHE_SIZE);
+ }
+
lock_kernel();
status = nfs_updatepage(file, page, offset, copied);
unlock_kernel();