Re: [PATCH] mm/filemap: invalidating pages is still necessary when io with IOCB_NOWAIT

[Matthew Wilcox]

On Mon, May 13, 2024 at 09:23:39PM +0800, Liu Wei wrote:
> After commit (6be96d3ad3 fs: return if direct I/O will trigger writeback),

If you're reporting problems with a particular commit, it's good form
to cc the people who actually wrote that commit.

> when we issuing AIO with direct I/O and IOCB_NOWAIT on a block device, the
> process context will not be blocked.
> 
> However, if the device already has page cache in memory, EAGAIN will be
> returned. And even when trying to reissue the AIO with direct I/O and
> IOCB_NOWAIT again, we consistently receive EAGAIN.
> 
> Maybe a better way to deal with it: filemap_fdatawrite_range dirty pages
> with WB_SYNC_NONE flag, and invalidate_mapping_pages unmapped pages at
> the same time.
> 
> Signed-off-by: Liu Wei <liuwei09@xxxxxxxx>
> ---
>  mm/filemap.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 30de18c4fd28..1852a00caf31 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2697,8 +2697,15 @@ int kiocb_invalidate_pages(struct kiocb *iocb, size_t count)
>  
>  	if (iocb->ki_flags & IOCB_NOWAIT) {
>  		/* we could block if there are any pages in the range */
> -		if (filemap_range_has_page(mapping, pos, end))
> +		if (filemap_range_has_page(mapping, pos, end)) {
> +			if (mapping_needs_writeback(mapping)) {
> +				__filemap_fdatawrite_range(mapping,
> +						pos, end, WB_SYNC_NONE);
> +			}
> +			invalidate_mapping_pages(mapping,
> +					pos >> PAGE_SHIFT, end >> PAGE_SHIFT);
>  			return -EAGAIN;
> +		}
>  	} else {
>  		ret = filemap_write_and_wait_range(mapping, pos, end);
>  		if (ret)
> -- 
> 2.42.1
> 
> 
>