linux-kernel - Re: [PATCH] f2fs: let background GC being aware of freezing

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Date:   Sat, 22 Jul 2017 08:47:45 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <yuchao0@...wei.com>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] f2fs: let background GC being aware of freezing

Hi Jaegeuk,

On 2017/7/22 4:54, Jaegeuk Kim wrote:
> Hi Chao,
> 
> On 07/21, Chao Yu wrote:
>> When ->freeze_fs is called from lvm for doing snapshot, it needs to
>> make sure there will be no more changes in filesystem's data, however,
>> previously, background GC wasn't aware of freezing, so in environment
>> with active background GC thread, data of snapshot becomes unstable.
> 
> What about flush/discard threads?

Updated.

Thanks,

> 
> Thanks,
> 
>>
>> This patch fixes this issue by adding sb_{start,end}_intwrite in GC
>> flow.
>>
>> Signed-off-by: Chao Yu <yuchao0@...wei.com>
>> ---
>>  fs/f2fs/gc.c | 8 ++++++--
>>  1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>> index 76ad2c3d88db..1c0117f60083 100644
>> --- a/fs/f2fs/gc.c
>> +++ b/fs/f2fs/gc.c
>> @@ -55,6 +55,8 @@ static int gc_thread_func(void *data)
>>  		}
>>  #endif
>>  
>> +		sb_start_intwrite(sbi->sb);
>> +
>>  		/*
>>  		 * [GC triggering condition]
>>  		 * 0. GC is not conducted currently.
>> @@ -69,12 +71,12 @@ static int gc_thread_func(void *data)
>>  		 * So, I'd like to wait some time to collect dirty segments.
>>  		 */
>>  		if (!mutex_trylock(&sbi->gc_mutex))
>> -			continue;
>> +			goto next;
>>  
>>  		if (!is_idle(sbi)) {
>>  			increase_sleep_time(gc_th, &wait_ms);
>>  			mutex_unlock(&sbi->gc_mutex);
>> -			continue;
>> +			goto next;
>>  		}
>>  
>>  		if (has_enough_invalid_blocks(sbi))
>> @@ -93,6 +95,8 @@ static int gc_thread_func(void *data)
>>  
>>  		/* balancing f2fs's metadata periodically */
>>  		f2fs_balance_fs_bg(sbi);
>> +next:
>> +		sb_end_intwrite(sbi->sb);
>>  
>>  	} while (!kthread_should_stop());
>>  	return 0;
>> -- 
>> 2.13.1.388.g69e6b9b4f4a9