On 05/09/2018 02:48 AM, Christoph Hellwig wrote:
> After already supporting a simple implementation of buffered writes for
> the blocksize == PAGE_SIZE case in the last commit this adds full support
> even for smaller block sizes. There are three bits of per-block
> information in the buffer_head structure that really matter for the iomap
> read and write path:
>
> - uptodate status (BH_uptodate)
> - marked as currently under read I/O (BH_Async_Read)
> - marked as currently under write I/O (BH_Async_Write)
>
> Instead of having new per-block structures this now adds a per-page
> structure called struct iomap_page to track this information in a slightly
> different form:
>
> - a bitmap for the per-block uptodate status. For worst case of a 64k
> page size system this bitmap needs to contain 128 bits. For the
> typical 4k page size case it only needs 8 bits, although we still
> need a full unsigned long due to the way the atomic bitmap API works.
> - two atomic_t counters are used to track the outstanding read and write
> counts
>
> There is quite a bit of boilerplate code as the buffered I/O path uses
> various helper methods, but the actual code is very straight forward.
>
> In this commit the code can't actually be used yet, as we need to
> switch from the old implementation to the new one together with the
> XFS writeback code.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> fs/iomap.c | 262 +++++++++++++++++++++++++++++++++++++-----
> include/linux/iomap.h | 32 ++++++
> 2 files changed, 264 insertions(+), 30 deletions(-)
>
> diff --git a/fs/iomap.c b/fs/iomap.c
> index a3861945504f..4e7ac6aa88ef 100644
> --- a/fs/iomap.c
> +++ b/fs/iomap.c
> @@ -17,6 +17,7 @@
> #include <linux/iomap.h>
> #include <linux/uaccess.h>
> #include <linux/gfp.h>
> +#include <linux/migrate.h>
> #include <linux/mm.h>
> #include <linux/mm_inline.h>
> #include <linux/swap.h>
> @@ -109,6 +110,107 @@ iomap_block_needs_zeroing(struct inode *inode, loff_t pos, struct iomap *iomap)
> return iomap->type != IOMAP_MAPPED || pos > i_size_read(inode);
> }
>
> +static struct iomap_page *
> +iomap_page_create(struct inode *inode, struct page *page)
> +{
> + struct iomap_page *iop = to_iomap_page(page);
> +
> + if (iop || i_blocksize(inode) == PAGE_SIZE)
> + return iop;
Why is this an equal comparison operator? Shouldn't this be >= to
include filesystem blocksize greater than PAGE_SIZE?
--
Goldwyn
