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Subject: Re: [PATCH v2] f2fs: fix to avoid touching checkpointed data in
 get_victim()
To:     Jaegeuk Kim <jaegeuk@kernel.org>
CC:     <linux-f2fs-devel@lists.sourceforge.net>,
        <linux-kernel@vger.kernel.org>, <chao@kernel.org>
References: <20210324031828.67133-1-yuchao0@huawei.com>
 <YFvQGxLbpmDjxEzR@google.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <2dfb085b-80ce-050b-5650-986675a07488@huawei.com>
Date:   Fri, 26 Mar 2021 15:33:22 +0800
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On 2021/3/25 7:49, Jaegeuk Kim wrote:
> On 03/24, Chao Yu wrote:
>> In CP disabling mode, there are two issues when using LFS or SSR | AT_SSR
>> mode to select victim:
>>
>> 1. LFS is set to find source section during GC, the victim should have
>> no checkpointed data, since after GC, section could not be set free for
>> reuse.
>>
>> Previously, we only check valid chpt blocks in current segment rather
>> than section, fix it.
>>
>> 2. SSR | AT_SSR are set to find target segment for writes which can be
>> fully filled by checkpointed and newly written blocks, we should never
>> select such segment, otherwise it can cause panic or data corruption
>> during allocation, potential case is described as below:
>>
>>   a) target segment has 128 ckpt valid blocks
>>   b) GC migrates 'n' (n < 512) valid blocks to other segment (segment is
>>      still in dirty list)

I missed to change 128 to n, so comments should be updated as below:

   a) target segment has 'n' (n < 512) ckpt valid blocks
   b) GC migrates 'n' valid blocks to other segment (segment is still
      in dirty list)

Thanks,

>>   c) GC migrates '512 - n' blocks to target segment (segment has 'n'
>>      cp_vblocks and '512 - n' vblocks)
>>   d) If GC selects target segment via {AT,}SSR allocator, however there
>>      is no free space in targe segment.