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From: Chao Yu <chao@kernel.org>
To: Daeho Jeong <daeho43@gmail.com>
Cc: linux-kernel@vger.kernel.org,
	linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com,
	Daeho Jeong <daehojeong@google.com>
Subject: Re: [f2fs-dev] [PATCH v2] f2fs: introduce fragment allocation mode mount option
Date: Sat, 28 Aug 2021 08:43:11 +0800	[thread overview]
Message-ID: <335d5bb5-7055-c934-33df-a03885382034@kernel.org> (raw)
In-Reply-To: <CACOAw_yhgo1_wrejKskSm=Rsw27ogx=TS_A=z=-NGLcecA-gYA@mail.gmail.com>

On 2021/8/27 23:22, Daeho Jeong wrote:
>> I'd like to add a fixed chunk/hole fragmentation mode in addition, then
>> userspace can control the fragmented chunk/hole with fixed size.
>>
>> How do you think of renaming "fragment:block" to "fragment:rand_block", and
>> then I can add "fragment:fixed_block" option and its logic in addition?
>>
> 
> The reason I added the randomness on these values is the segment
> selection in SSR mode.
> If all the segments have the same free block counts, f2fs will
> allocate a new segment sequentially in SSR.

I'm fine with this, since test program can customize different fragment
degree on segments by setting different chunk/hole size.

> This was what I didn't want. Plus, in the real world, the size of hole
> and chunk will be different in different segments.
> 
> But, if you think we need this "fragment:fixed_block" mode, I am happy
> to have it. :)

Thanks a lot. :)

As you said it needs to be aligned to real world fragmentation, I notice that:
with this way, we can't simulate similar fragment in FTL, due to its page
mapping architecture, all fragmented data/node in filesystem will be written
sequentially into its blocks.

In order to simulate fragment in FTL, we need to:
- write data (chunk size) with dummy pages (hole size) to devices
- issue discards on those holes

I guess fragmenting device (erase blocks) at the same time wouldn't be
original intention of this patch, right?

Thanks,

> 
>> Do we need to consider multiple thread scenario? in such case,
>> .fragment_remained_chunk may update randomly.
>>
>> In addition, multiple log headers share one .fragment_remained_chunk,
>> it may cause unexpected result, it means there may be continuous holes
>> or chunks in locality due to swithing between different log headers.
>>
>> Thanks,
>>
> 
> Oh, I overlooked that point. I am going to add the variable for each
> segment as you said before.
> 
> Thanks,
> 

  reply	other threads:[~2021-08-28  0:43 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-25 18:57 Daeho Jeong
2021-08-27  5:26 ` [f2fs-dev] " Chao Yu
2021-08-27 15:22   ` Daeho Jeong
2021-08-28  0:43     ` Chao Yu [this message]
2021-08-30 17:27       ` Daeho Jeong

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