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Subject: Re: [PATCH] f2fs: introduce nosmall_discard mount option
To:     Christoph Hellwig <hch@infradead.org>
Cc:     jaegeuk@kernel.org, linux-f2fs-devel@lists.sourceforge.net,
        linux-kernel@vger.kernel.org, Chao Yu <chao.yu@linux.dev>
References: <20210730100530.4401-1-chao@kernel.org>
 <YQqbhMtVZvCF30r9@infradead.org>
From:   Chao Yu <chao@kernel.org>
Message-ID: <1204887a-7724-7891-2db5-6f710b595781@kernel.org>
Date:   Thu, 5 Aug 2021 09:22:50 +0800
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On 2021/8/4 21:52, Christoph Hellwig wrote:
> On Fri, Jul 30, 2021 at 06:05:30PM +0800, Chao Yu wrote:
>> This patch introduces a new mountoption "nosmall_discard" to support
>> disabling small discard functionality, note that the mountoption can not
>> be removed by remount() due to related metadata should always be
>> initialized during mount().
> 
> Why does this need an option?  It should be enable IFF and only IFF a
> SMR drive is detected.
> 

We've updated this patch as below:

@@ -1961,10 +1998,13 @@ static void default_options(struct f2fs_sb_info *sbi)
  	sbi->sb->s_flags |= SB_LAZYTIME;
  	set_opt(sbi, FLUSH_MERGE);
  	set_opt(sbi, DISCARD);
-	if (f2fs_sb_has_blkzoned(sbi))
+	if (f2fs_sb_has_blkzoned(sbi)) {
  		F2FS_OPTION(sbi).fs_mode = FS_MODE_LFS;
-	else
+		F2FS_OPTION(sbi).discard_unit = DISCARD_UNIT_SECTION;
+	} else {
  		F2FS_OPTION(sbi).fs_mode = FS_MODE_ADAPTIVE;
+		F2FS_OPTION(sbi).discard_unit = DISCARD_UNIT_BLOCK;
+	}

https://git.kernel.org/pub/scm/linux/kernel/git/chao/linux.git/commit/?h=dev&id=4f993264fe2965c344f223d854ccbb549b16ed71

For blkzoned device, section unit based discard will be enabled by default.

For other type of devices, IMO, this is a tradeoff in between small-sized
discard support and memory overhead, so I proposed to add such mount option
to support selection from different benefit point.

Thanks,