mm: remove optimizations based on i_size in mapping writeback waits

Marcelo added this i_size based optimization with a patch in 2004
(commitid is from the linux-history tree):

    commit 765dad09b4ac101a32d87af2bb793c3060497d3c
    Author: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
    Date:   Tue Sep 7 17:51:17 2004 -0700

	small wait_on_page_writeback_range() optimization

	filemap_fdatawait() calls wait_on_page_writeback_range() with -1
	as "end" parameter.  This is not needed since we know the EOF
	from the inode.  Use that instead.

There may be races here, particularly with clustered or network
filesystems. It also seems like a bit of a layering violation since
we're operating on an address_space here, not an inode.

Finally, it's also questionable whether this optimization really helps
on workloads that we care about. Should we be optimizing for writeback
vs. truncate races in a codepath where we expect to wait anyway? It
doesn't seem worth the risk.

Remove this optimization from the filemap_fdatawait codepaths. This
means that filemap_fdatawait becomes a trivial wrapper around
filemap_fdatawait_range.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jeff Layton <jlayton@redhat.com>

1 files changed, 1 insertions, 29 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 394bb5e..85dfe3b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -512,39 +512,11 @@ EXPORT_SYMBOL(file_fdatawait_range);
  */
 int filemap_fdatawait_keep_errors(struct address_space *mapping)
 {
-	loff_t i_size = i_size_read(mapping->host);
-
-	if (i_size == 0)
-		return 0;
-
-	__filemap_fdatawait_range(mapping, 0, i_size - 1);
+	__filemap_fdatawait_range(mapping, 0, LLONG_MAX);
 	return filemap_check_and_keep_errors(mapping);
 }
 EXPORT_SYMBOL(filemap_fdatawait_keep_errors);
 
-/**
- * filemap_fdatawait - wait for all under-writeback pages to complete
- * @mapping: address space structure to wait for
- *
- * Walk the list of under-writeback pages of the given address space
- * and wait for all of them.  Check error status of the address space
- * and return it.
- *
- * Since the error status of the address space is cleared by this function,
- * callers are responsible for checking the return value and handling and/or
- * reporting the error.
- */
-int filemap_fdatawait(struct address_space *mapping)
-{
-	loff_t i_size = i_size_read(mapping->host);
-
-	if (i_size == 0)
-		return 0;
-
-	return filemap_fdatawait_range(mapping, 0, i_size - 1);
-}
-EXPORT_SYMBOL(filemap_fdatawait);
-
 static bool mapping_needs_writeback(struct address_space *mapping)
 {
 	return (!dax_mapping(mapping) && mapping->nrpages) ||