linux-kernel - Re: [RFC PATCH 0/2] apply write hints to select the type of segments

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Date:   Thu, 9 Nov 2017 17:12:57 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Hyunchul Lee <hyc.lee@...il.com>, Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, <kernel-team@....com>,
        Hyunchul Lee <cheol.lee@....com>, Chao Yu <yuchao0@...wei.com>
Subject: Re: [RFC PATCH 0/2] apply write hints to select the type of segments

On 2017/11/9 13:51, Hyunchul Lee wrote:
> From: Hyunchul Lee <cheol.lee@....com>
> 
> Using write hints[1], applications can inform the life time of the data
> written to devices. and this[2] reported that the write hints patch
> decreased writes in NAND by 25%.
> 
> This hints help F2FS to determine the followings.
>   1) the segment types where the data will be written.
>   2) the hints that will be passed down to devices with the data of segments.
> 
> This patch set implements the first mapping from write hints to segment types
> as shown below.
> 
>   hints                     segment type
>   -----                     ------------
>   WRITE_LIFE_SHORT          CURSEG_COLD_DATA
>   WRITE_LIFE_EXTREME        CURSEG_HOT_DATA
>   others                    CURSEG_WARM_DATA
> 
> The F2FS poliy for hot/cold seperation has precedence over this hints, And
> hints are not applied in in-place update.

Could we change to disable IPU if file/inode write hint is existing?

> 
> Before the second mapping is implemented, write hints are not passed down
> to devices. Because it is better that the data of a segment have the same 
> hint.
> 
> [1]: c75b1d9421f80f4143e389d2d50ddfc8a28c8c35
> [2]: https://lwn.net/Articles/726477/

Could you write a patch to support passing write hint to block layer for
buffered writes as below commit:
0127251c45ae ("ext4: add support for passing in write hints for buffered writes")

Thanks,

> 
> Hyunchul Lee (2):
>   f2fs: apply write hints to select the type of segments for buffered
>     write
>   f2fs: apply write hints to select the type of segment for direct write
> 
>  fs/f2fs/data.c    | 101 ++++++++++++++++++++++++++++++++----------------------
>  fs/f2fs/f2fs.h    |   1 +
>  fs/f2fs/segment.c |  14 +++++++-
>  3 files changed, 74 insertions(+), 42 deletions(-)
>