Hi,
On 31/07/17 12:27, Jeff Layton wrote:
On Thu, 2017-07-27 at 08:48 -0400, Jeff Layton wrote:
On Thu, 2017-07-27 at 10:49 +0200, Jan Kara wrote:
On Wed 26-07-17 13:55:36, Jeff Layton wrote:
+int file_write_and_wait(struct file *file)
+{
+ int err = 0, err2;
+ struct address_space *mapping = file->f_mapping;
+
+ if ((!dax_mapping(mapping) && mapping->nrpages) ||
+ (dax_mapping(mapping) && mapping->nrexceptional)) {
+ err = filemap_fdatawrite(mapping);
+ /* See comment of filemap_write_and_wait() */
+ if (err != -EIO) {
+ loff_t i_size = i_size_read(mapping->host);
+
+ if (i_size != 0)
+ __filemap_fdatawait_range(mapping, 0,
+ i_size - 1);
+ }
+ }
Err, what's the i_size check doing here? I'd just pass ~0 as the end of the
range and ignore i_size. It is much easier than trying to wrap your head
around possible races with file operations modifying i_size.
Honza
I'm basically emulating _exactly_ what filemap_write_and_wait does here,
as I'm leery of making subtle behavior changes in the actual writeback
behavior. For example:
-----------------8<----------------
static inline int __filemap_fdatawrite(struct address_space *mapping,
int sync_mode)
{
return __filemap_fdatawrite_range(mapping, 0, LLONG_MAX, sync_mode);
}
int filemap_fdatawrite(struct address_space *mapping)
{
return __filemap_fdatawrite(mapping, WB_SYNC_ALL);
}
EXPORT_SYMBOL(filemap_fdatawrite);
-----------------8<----------------
...which then sets up the wbc with the right ranges and sync mode and
kicks off writepages. But then, it does the i_size_read to figure out
what range it should wait on (with the shortcut for the size == 0 case).
My assumption was that it was intentionally designed that way, but I'm
guessing from your comments that it wasn't? If so, then we can turn
file_write_and_wait a static inline wrapper around
file_write_and_wait_range.
FWIW, I did a bit of archaeology in the linux-history tree and found
this patch from Marcelo in 2004. Is this optimization still helpful? If
not, then that does simplify the code a bit.
-------------------8<--------------------
[PATCH] 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.
Signed-off-by: Marcelo Tosatti <marcelo.tosatti@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxx>
---
mm/filemap.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/mm/filemap.c b/mm/filemap.c
index 78e18b7639b6..55fb7b4141e4 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -287,7 +287,13 @@ EXPORT_SYMBOL(sync_page_range);
*/
int filemap_fdatawait(struct address_space *mapping)
{
- return wait_on_page_writeback_range(mapping, 0, -1);
+ loff_t i_size = i_size_read(mapping->host);
+
+ if (i_size == 0)
+ return 0;
+
+ return wait_on_page_writeback_range(mapping, 0,
+ (i_size - 1) >> PAGE_CACHE_SHIFT);
}
EXPORT_SYMBOL(filemap_fdatawait);
Does this ever get called in cases where we would not hold fs locks? In
that case we definitely don't want to be relying on i_size,
Steve.
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