RE: [f2fs-dev] [PATCH] f2fs: introduce a new direct_IO write path

[Chao Yu]

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk.kim@xxxxxxxxxxx]
> Sent: Wednesday, December 18, 2013 8:12 AM
> To: linux-fsdevel@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
> Subject: Re: [f2fs-dev] [PATCH] f2fs: introduce a new direct_IO write path
> 
> Change log from v1:
>  o fix NOSPC error handling
> 
> >From b8511a74fe98b67247a9feeed58441e8f5ffd705 Mon Sep 17 00:00:00 2001
> From: Jaegeuk Kim <jaegeuk.kim@xxxxxxxxxxx>
> Date: Mon, 16 Dec 2013 19:04:05 +0900
> Subject: [PATCH] f2fs: introduce a new direct_IO write path
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx,
> linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
> 
> Previously, f2fs doesn't support direct IOs with high performance, which
> throws
> every write requests via the buffered write path, resulting in highly
> performance degradation due to memory opeations like copy_from_user.
> 
> This patch introduces a new direct IO path in which every write requests
> are
> processed by generic blockdev_direct_IO() with enhanced get_block
> function.
> 
> The get_data_block() in f2fs handles:
> 1. if original data blocks are allocates, then give them to blockdev.
> 2. otherwise,
>   a. preallocate requested block addresses
>   b. do not use extent cache for better performance
>   c. give the block addresses to blockdev
> 
> This policy induces that:
> - new allocated data are sequentially written to the disk
> - updated data are randomly written to the disk.
> - f2fs gives consistency on its file meta, not file data.

Looks Nice!

> 
> Signed-off-by: Jaegeuk Kim <jaegeuk.kim@xxxxxxxxxxx>

Reviewed-by: Chao Yu <chao2.yu@xxxxxxxxxxx>

> +
> +	end_offset = IS_INODE(dn.node_page) ?
> +			ADDRS_PER_INODE(F2FS_I(inode)) : ADDRS_PER_BLOCK;
> +	bh_result->b_size = (((size_t)1) << blkbits);
> +	dn.ofs_in_node++;
> +	pgofs++;
> +
> +get_next:
> +	if (dn.ofs_in_node >= end_offset) {
> +		if (allocated)
> +			sync_inode_page(&dn);
> +		allocated = false;

		if (allocated) {
			sync_inode_page(&dn);
			allocated = false;
		}
Certainly, it's really not a big deal. :)

Thanks

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