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authorGoldwyn Rodrigues <rgoldwyn@suse.com>2017-06-20 07:05:44 -0500
committerJens Axboe <axboe@kernel.dk>2017-06-20 07:12:03 -0600
commit6be96d3ad34a124450028dabba43f07fe1d0c86d (patch)
treea5f6ef95a01e38caa3dc1e50071d5baa78426a3f /mm
parentb745fafaf70c0a98a2e1e7ac8cb14542889ceb0e (diff)
fs: return if direct I/O will trigger writeback
Find out if the I/O will trigger a wait due to writeback. If yes, return -EAGAIN. Return -EINVAL for buffered AIO: there are multiple causes of delay such as page locks, dirty throttling logic, page loading from disk etc. which cannot be taken care of. Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jan Kara <jack@suse.cz> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'mm')
-rw-r--r--mm/filemap.c32
1 files changed, 25 insertions, 7 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index 9b39a2390b9e..742034e56100 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2070,10 +2070,17 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
loff_t size;
size = i_size_read(inode);
- retval = filemap_write_and_wait_range(mapping, iocb->ki_pos,
- iocb->ki_pos + count - 1);
- if (retval < 0)
- goto out;
+ if (iocb->ki_flags & IOCB_NOWAIT) {
+ if (filemap_range_has_page(mapping, iocb->ki_pos,
+ iocb->ki_pos + count - 1))
+ return -EAGAIN;
+ } else {
+ retval = filemap_write_and_wait_range(mapping,
+ iocb->ki_pos,
+ iocb->ki_pos + count - 1);
+ if (retval < 0)
+ goto out;
+ }
file_accessed(file);
@@ -2674,6 +2681,9 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
pos = iocb->ki_pos;
+ if ((iocb->ki_flags & IOCB_NOWAIT) && !(iocb->ki_flags & IOCB_DIRECT))
+ return -EINVAL;
+
if (limit != RLIM_INFINITY) {
if (iocb->ki_pos >= limit) {
send_sig(SIGXFSZ, current, 0);
@@ -2742,9 +2752,17 @@ generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
write_len = iov_iter_count(from);
end = (pos + write_len - 1) >> PAGE_SHIFT;
- written = filemap_write_and_wait_range(mapping, pos, pos + write_len - 1);
- if (written)
- goto out;
+ if (iocb->ki_flags & IOCB_NOWAIT) {
+ /* If there are pages to writeback, return */
+ if (filemap_range_has_page(inode->i_mapping, pos,
+ pos + iov_iter_count(from)))
+ return -EAGAIN;
+ } else {
+ written = filemap_write_and_wait_range(mapping, pos,
+ pos + write_len - 1);
+ if (written)
+ goto out;
+ }
/*
* After a write we want buffered reads to be sure to go to disk to get