linux-ext4 - Re: [PATCH 16/17] block: use iomap for writes to block devices

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Date:   Fri, 19 May 2023 16:22:01 +0200
From:   Hannes Reinecke <hare@...e.de>
To:     Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>
Cc:     Miklos Szeredi <miklos@...redi.hu>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        ceph-devel@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, cluster-devel@...hat.com,
        linux-xfs@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 16/17] block: use iomap for writes to block devices

On 4/24/23 07:49, Christoph Hellwig wrote:
> Use iomap in buffer_head compat mode to write to block devices.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>   block/Kconfig |  1 +
>   block/fops.c  | 33 +++++++++++++++++++++++++++++----
>   2 files changed, 30 insertions(+), 4 deletions(-)
> 
> diff --git a/block/Kconfig b/block/Kconfig
> index 941b2dca70db73..672b08f0096ab4 100644
> --- a/block/Kconfig
> +++ b/block/Kconfig
> @@ -5,6 +5,7 @@
>   menuconfig BLOCK
>          bool "Enable the block layer" if EXPERT
>          default y
> +       select IOMAP
>          select SBITMAP
>          help
>   	 Provide block layer support for the kernel.
> diff --git a/block/fops.c b/block/fops.c
> index 318247832a7bcf..7910636f8df33b 100644
> --- a/block/fops.c
> +++ b/block/fops.c
> @@ -15,6 +15,7 @@
>   #include <linux/falloc.h>
>   #include <linux/suspend.h>
>   #include <linux/fs.h>
> +#include <linux/iomap.h>
>   #include <linux/module.h>
>   #include "blk.h"
>   
> @@ -386,6 +387,27 @@ static ssize_t blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
>   	return __blkdev_direct_IO(iocb, iter, bio_max_segs(nr_pages));
>   }
>   
> +static int blkdev_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> +		unsigned int flags, struct iomap *iomap, struct iomap *srcmap)
> +{
> +	struct block_device *bdev = I_BDEV(inode);
> +	loff_t isize = i_size_read(inode);
> +
> +	iomap->bdev = bdev;
> +	iomap->offset = ALIGN_DOWN(offset, bdev_logical_block_size(bdev));
> +	if (WARN_ON_ONCE(iomap->offset >= isize))
> +		return -EIO;

I'm hitting this during booting:
[    5.016324]  <TASK>
[    5.030256]  iomap_iter+0x11a/0x350
[    5.030264]  iomap_readahead+0x1eb/0x2c0
[    5.030272]  read_pages+0x5d/0x220
[    5.030279]  page_cache_ra_unbounded+0x131/0x180
[    5.030284]  filemap_get_pages+0xff/0x5a0
[    5.030292]  filemap_read+0xca/0x320
[    5.030296]  ? aa_file_perm+0x126/0x500
[    5.040216]  ? touch_atime+0xc8/0x150
[    5.040224]  blkdev_read_iter+0xb0/0x150
[    5.040228]  vfs_read+0x226/0x2d0
[    5.040234]  ksys_read+0xa5/0xe0
[    5.040238]  do_syscall_64+0x5b/0x80

Maybe we should consider this patch:

diff --git a/block/fops.c b/block/fops.c
index 524b8a828aad..d202fb663f25 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -386,10 +386,13 @@ static int blkdev_iomap_begin(struct inode *inode, 
loff_t offset, loff_t length,

         iomap->bdev = bdev;
         iomap->offset = ALIGN_DOWN(offset, bdev_logical_block_size(bdev));
-       if (WARN_ON_ONCE(iomap->offset >= isize))
-               return -EIO;
-       iomap->type = IOMAP_MAPPED;
-       iomap->addr = iomap->offset;
+       if (WARN_ON_ONCE(iomap->offset >= isize)) {
+               iomap->type = IOMAP_HOLE;
+               iomap->addr = IOMAP_NULL_ADDR;
+       } else {
+               iomap->type = IOMAP_MAPPED;
+               iomap->addr = iomap->offset;
+       }
         iomap->length = isize - iomap->offset;
         if (IS_ENABLED(CONFIG_BUFFER_HEAD))
                 iomap->flags |= IOMAP_F_BUFFER_HEAD;


Other that the the system seems fine.

Cheers,

Hannes