On Mon, Feb 03, 2025 at 09:32:38AM -0700, Jens Axboe wrote:
> Add iomap buffered write support for RWF_DONTCACHE. If RWF_DONTCACHE is
> set for a write, mark the folios being written as uncached. Then
> writeback completion will drop the pages. The write_iter handler simply
> kicks off writeback for the pages, and writeback completion will take
> care of the rest.
>
> This still needs the user of the iomap buffered write helpers to call
> folio_end_dropbehind_write() upon successful issue of the writes.
I thought iomap calls folio_end_writeback, which cares of that? So xfs
doesn't itself have to call folio_end_dropbehind_write?
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> ---
> fs/iomap/buffered-io.c | 4 ++++
> include/linux/iomap.h | 1 +
> 2 files changed, 5 insertions(+)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index d303e6c8900c..ea863c3cf510 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -603,6 +603,8 @@ struct folio *iomap_get_folio(struct iomap_iter *iter, loff_t pos, size_t len)
>
> if (iter->flags & IOMAP_NOWAIT)
> fgp |= FGP_NOWAIT;
> + if (iter->flags & IOMAP_DONTCACHE)
> + fgp |= FGP_DONTCACHE;
> fgp |= fgf_set_order(len);
>
> return __filemap_get_folio(iter->inode->i_mapping, pos >> PAGE_SHIFT,
> @@ -1034,6 +1036,8 @@ iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *i,
>
> if (iocb->ki_flags & IOCB_NOWAIT)
> iter.flags |= IOMAP_NOWAIT;
> + if (iocb->ki_flags & IOCB_DONTCACHE)
> + iter.flags |= IOMAP_DONTCACHE;
>
> while ((ret = iomap_iter(&iter, ops)) > 0)
> iter.processed = iomap_write_iter(&iter, i);
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 75bf54e76f3b..26b0dbe23e62 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -183,6 +183,7 @@ struct iomap_folio_ops {
> #define IOMAP_DAX 0
> #endif /* CONFIG_FS_DAX */
> #define IOMAP_ATOMIC (1 << 9)
> +#define IOMAP_DONTCACHE (1 << 10)
This needs a mention in the iomap documentation. If the patch below
accurately summarizes what it does nowadays, then you can add it to the
series with a:
Signed-off-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
--D
diff --git a/Documentation/filesystems/iomap/design.rst b/Documentation/filesystems/iomap/design.rst
index b0d0188a095e55..7b91546750f59e 100644
--- a/Documentation/filesystems/iomap/design.rst
+++ b/Documentation/filesystems/iomap/design.rst
@@ -352,6 +352,11 @@ operations:
``IOMAP_NOWAIT`` is often set on behalf of ``IOCB_NOWAIT`` or
``RWF_NOWAIT``.
+ * ``IOMAP_DONTCACHE`` is set when the caller wishes to perform a
+ buffered file I/O and would like the kernel to drop the pagecache
+ after the I/O completes, if it isn't already being used by another
+ thread.
+
If it is necessary to read existing file contents from a `different
<https://lore.kernel.org/all/20191008071527.29304-9-hch@xxxxxx/>`_
device or address range on a device, the filesystem should return that
diff --git a/Documentation/filesystems/iomap/operations.rst b/Documentation/filesystems/iomap/operations.rst
index 2c7f5df9d8b037..584ff549f9a659 100644
--- a/Documentation/filesystems/iomap/operations.rst
+++ b/Documentation/filesystems/iomap/operations.rst
@@ -131,6 +131,8 @@ These ``struct kiocb`` flags are significant for buffered I/O with iomap:
* ``IOCB_NOWAIT``: Turns on ``IOMAP_NOWAIT``.
+ * ``IOCB_DONTCACHE``: Turns on ``IOMAP_DONTCACHE``.
+
Internal per-Folio State
------------------------
