linux-kernel - Re: [f2fs-dev] [PATCH 2/3] f2fs: run GCs synchronously given user requests

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Date:   Wed, 22 Jun 2022 22:02:29 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 2/3] f2fs: run GCs synchronously given user
 requests

On 2022/6/20 6:34, Jaegeuk Kim wrote:
> On 06/19, Chao Yu wrote:
>> On 2022/6/18 6:31, Jaegeuk Kim wrote:
>>> When users set GC_URGENT or GC_MID, they expected to do GCs right away.
>>> But, there's a condition to bypass it. Let's indicate we need to do now
>>> in the thread.
>>
>> .should_migrate_blocks is used to force migrating blocks in full
>> section, so what is the condition here? GC should not never select
>> a full section, right?
> 
> I think it'll move a full section given .victim_segno is not NULL_SEGNO,
> as __get_victim will give a dirty segment all the time. wdyt?

However, in gc_thread_fun() victim_segno is NULL_SEGNO all the time.

I guess .should_migrate_blocks should only be set to true for
F2FS_IOC_FLUSH_DEVICE/F2FS_IOC_RESIZE_FS case? rather than GC_URGENT or GC_MID
case? See commit 7dede88659df ("f2fs: fix to allow migrating fully valid segment").

Thanks,

> 
>>
>> Thanks,
>>
>>>
>>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
>>> ---
>>>    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 d5fb426e0747..f4aa3c88118b 100644
>>> --- a/fs/f2fs/gc.c
>>> +++ b/fs/f2fs/gc.c
>>> @@ -37,7 +37,6 @@ static int gc_thread_func(void *data)
>>>    	unsigned int wait_ms;
>>>    	struct f2fs_gc_control gc_control = {
>>>    		.victim_segno = NULL_SEGNO,
>>> -		.should_migrate_blocks = false,
>>>    		.err_gc_skipped = false };
>>>    	wait_ms = gc_th->min_sleep_time;
>>> @@ -113,7 +112,10 @@ static int gc_thread_func(void *data)
>>>    				sbi->gc_mode == GC_URGENT_MID) {
>>>    			wait_ms = gc_th->urgent_sleep_time;
>>>    			f2fs_down_write(&sbi->gc_lock);
>>> +			gc_control.should_migrate_blocks = true;
>>>    			goto do_gc;
>>> +		} else {
>>> +			gc_control.should_migrate_blocks = false;
>>>    		}
>>>    		if (foreground) {
>>> @@ -139,7 +141,9 @@ static int gc_thread_func(void *data)
>>>    		if (!foreground)
>>>    			stat_inc_bggc_count(sbi->stat_info);
>>> -		sync_mode = F2FS_OPTION(sbi).bggc_mode == BGGC_MODE_SYNC;
>>> +		sync_mode = F2FS_OPTION(sbi).bggc_mode == BGGC_MODE_SYNC ||
>>> +				sbi->gc_mode == GC_URGENT_HIGH ||
>>> +				sbi->gc_mode == GC_URGENT_MID;
>>>    		/* foreground GC was been triggered via f2fs_balance_fs() */
>>>    		if (foreground)