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Date: Thu, 25 May 2017 10:32:32 +0200 From: Jan Kara <jack@...e.cz> To: Goldwyn Rodrigues <rgoldwyn@...e.de> Cc: linux-fsdevel@...r.kernel.org, jack@...e.com, hch@...radead.org, linux-block@...r.kernel.org, linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org, axboe@...nel.dk, linux-api@...r.kernel.org, adam.manzanares@....com, viro@...iv.linux.org.uk, Goldwyn Rodrigues <rgoldwyn@...e.com> Subject: Re: [PATCH 05/10] fs: return if direct write will trigger writeback On Wed 24-05-17 11:41:45, Goldwyn Rodrigues wrote: > From: Goldwyn Rodrigues <rgoldwyn@...e.com> > > Find out if the write 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. > > Signed-off-by: Goldwyn Rodrigues <rgoldwyn@...e.com> > Reviewed-by: Christoph Hellwig <hch@....de> Looks good. You can add: Reviewed-by: Jan Kara <jack@...e.cz> Honza > --- > mm/filemap.c | 17 ++++++++++++++--- > 1 file changed, 14 insertions(+), 3 deletions(-) > > diff --git a/mm/filemap.c b/mm/filemap.c > index 097213275461..bc146efa6815 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -2675,6 +2675,9 @@ 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); > @@ -2743,9 +2746,17 @@ 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 > -- > 2.12.0 > -- Jan Kara <jack@...e.com> SUSE Labs, CR
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