linux-kernel - Re: [PATCH v1] f2fs: fix to ensure queued discard commands are properly issued

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Message-ID: <CACOAw_x2v9fhorDWx9+f4VufddSPA5S6PF22AM_56smjjD5Faw@mail.gmail.com>
Date: Fri, 21 Feb 2025 07:56:46 -0800
From: Daeho Jeong <daeho43@...il.com>
To: Chao Yu <chao@...nel.org>
Cc: Yohan Joung <jyh429@...il.com>, jaegeuk@...nel.org, 
	linux-f2fs-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org, 
	Yohan Joung <yohan.joung@...com>
Subject: Re: [PATCH v1] f2fs: fix to ensure queued discard commands are
 properly issued

On Mon, Feb 17, 2025 at 4:38 AM Chao Yu <chao@...nel.org> wrote:
>
> On 2/4/25 22:53, Yohan Joung wrote:
> > F2FS zone storage requires discard and reset zone for each conventional,
> > zoned device.
> > In the current configuration, Discard granularity is set to the zone
> > size but queuing is inserted into the pend list with a maximum size of the
> > segment size As a result queued commands cannot be issued.
> > so we are restorting discard granularity to its original state
>
> It seems commit 4f993264fe29 ("f2fs: introduce discard_unit mount option")
> introduced a bug: when we enable discard_unit=section option, it will set
> .discard_granularity to BLKS_PER_SEC(), however discard granularity only
> supports [1, 512], once section size is not equal to segment size, it will
> cause bug. blkzoned feature became the victim since it use
> discard_unit=section option by default.
>
> What:           /sys/fs/f2fs/<disk>/discard_granularity
> Date:           July 2017
> Contact:        "Chao Yu" <yuchao0@...wei.com>
> Description:    Controls discard granularity of inner discard thread. Inner thread
>                 will not issue discards with size that is smaller than granularity.
>                 The unit size is one block(4KB), now only support configuring
>                 in range of [1, 512]. Default value is 16.
>                 For small devices, default value is 1.
>
> What about this?
>
> Subject: [PATCH] f2fs: fix to set .discard_granularity correctly
>
> commit 4f993264fe29 ("f2fs: introduce discard_unit mount option") introduced
> a bug, when we enable discard_unit=section option, it will set
> .discard_granularity to BLKS_PER_SEC(), however discard granularity only
> supports [1, 512], once section size is not equal to segment size, it will
> cause issue_discard_thread() in DPOLICY_BG mode will not select discard entry
> w/ any granularity to issue.
>
> Fixes: 4f993264fe29 ("f2fs: introduce discard_unit mount option")
> Signed-off-by: Yohan Joung <yohan.joung@...com>
> Signed-off-by: Chao Yu <chao@...nel.org>
> ---
>  fs/f2fs/segment.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 6ebe25eafafa..2b415926641f 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -2320,10 +2320,9 @@ static int create_discard_cmd_control(struct f2fs_sb_info *sbi)
>         dcc->discard_granularity = DEFAULT_DISCARD_GRANULARITY;
>         dcc->max_ordered_discard = DEFAULT_MAX_ORDERED_DISCARD_GRANULARITY;
>         dcc->discard_io_aware = DPOLICY_IO_AWARE_ENABLE;
> -       if (F2FS_OPTION(sbi).discard_unit == DISCARD_UNIT_SEGMENT)
> +       if (F2FS_OPTION(sbi).discard_unit == DISCARD_UNIT_SEGMENT ||
> +               F2FS_OPTION(sbi).discard_unit == DISCARD_UNIT_SECTION)
>                 dcc->discard_granularity = BLKS_PER_SEG(sbi);
> -       else if (F2FS_OPTION(sbi).discard_unit == DISCARD_UNIT_SECTION)
> -               dcc->discard_granularity = BLKS_PER_SEC(sbi);
>
>         INIT_LIST_HEAD(&dcc->entry_list);
>         for (i = 0; i < MAX_PLIST_NUM; i++)
> --
> 2.48.1.601.g30ceb7b040-goog
>

Reviewed-by: Daeho Jeong <daehojeong@...gle.com>

>