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Date: Wed, 1 Jul 2020 09:53:10 +0200 From: Christoph Hellwig <hch@....de> To: Goldwyn Rodrigues <rgoldwyn@...e.de> Cc: linux-fsdevel@...r.kernel.org, linux-btrfs@...r.kernel.org, fdmanana@...il.com, dsterba@...e.cz, david@...morbit.com, darrick.wong@...cle.com, hch@....de, Goldwyn Rodrigues <rgoldwyn@...e.com>, cluster-devel@...hat.com, linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org Subject: always fall back to buffered I/O after invalidation failures, was: Re: [PATCH 2/6] iomap: IOMAP_DIO_RWF_NO_STALE_PAGECACHE return if page invalidation fails On Mon, Jun 29, 2020 at 02:23:49PM -0500, Goldwyn Rodrigues wrote: > From: Goldwyn Rodrigues <rgoldwyn@...e.com> > > For direct I/O, add the flag IOMAP_DIO_RWF_NO_STALE_PAGECACHE to indicate > that if the page invalidation fails, return back control to the > filesystem so it may fallback to buffered mode. > > Reviewed-by: Darrick J. Wong <darrick.wong@...cle.com> > Signed-off-by: Goldwyn Rodrigues <rgoldwyn@...e.com> I'd like to start a discussion of this shouldn't really be the default behavior. If we have page cache that can't be invalidated it actually makes a whole lot of sense to not do direct I/O, avoid the warnings, etc. Adding all the relevant lists. > --- > fs/iomap/direct-io.c | 8 +++++++- > include/linux/iomap.h | 14 ++++++++++++++ > 2 files changed, 21 insertions(+), 1 deletion(-) > > diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c > index fd22bff61569..2459c76e41ab 100644 > --- a/fs/iomap/direct-io.c > +++ b/fs/iomap/direct-io.c > @@ -484,8 +484,14 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, > */ > ret = invalidate_inode_pages2_range(mapping, > pos >> PAGE_SHIFT, end >> PAGE_SHIFT); > - if (ret) > + if (ret) { > + if (dio_flags & IOMAP_DIO_RWF_NO_STALE_PAGECACHE) { > + if (ret == -EBUSY) > + ret = 0; > + goto out_free_dio; > + } > dio_warn_stale_pagecache(iocb->ki_filp); > + } > ret = 0; > > if (iov_iter_rw(iter) == WRITE && !wait_for_completion && > diff --git a/include/linux/iomap.h b/include/linux/iomap.h > index 8a4ba1635202..2ebb8a298cd8 100644 > --- a/include/linux/iomap.h > +++ b/include/linux/iomap.h > @@ -262,7 +262,21 @@ struct iomap_dio_ops { > /* > * Wait for completion of DIO > */ > + > #define IOMAP_DIO_RWF_SYNCIO (1 << 0) > +/* > + * Direct IO will attempt to keep the page cache coherent by > + * invalidating the inode's page cache over the range of the DIO. > + * That can fail if something else is actively using the page cache. > + * If this happens and the DIO continues, the data in the page > + * cache will become stale. > + * > + * Set this flag if you want the DIO to abort without issuing any IO > + * or error if it fails to invalidate the page cache successfully. > + * This allows the IO submitter to fallback to buffered IO to resubmit > + * IO > + */ > +#define IOMAP_DIO_RWF_NO_STALE_PAGECACHE (1 << 1) > > ssize_t iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, > const struct iomap_ops *ops, const struct iomap_dio_ops *dops, > -- > 2.26.2 ---end quoted text---
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