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

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Date:   Tue, 28 Jun 2022 15:59:01 +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 2022/6/23 0:58, Jaegeuk Kim wrote:
> On 06/22, Chao Yu wrote:
>> 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.
> 
> What do you mean? The gc_thread thread sets NULL_SEGNO, which prevents
> from selecting the full section. But, f2fs_ioc_flush_device will set the
> segno to move, and f2fs_resize_fs calls do_garbage_collect directly.

Yes, but I didn't get why this patch updates .should_migrate_blocks for
gc_thread_func() case? If this is added to avoid breaking from below condition,
I guess it's not necessary, since victim selected from gc_thread_func() will
always be dirty, so get_valid_blocks(sbi, segno, true) == BLKS_PER_SEC(sbi)
will be false anyway? or am I missing something?

		/*
		 * stop BG_GC if there is not enough free sections.
		 * Or, stop GC if the segment becomes fully valid caused by
		 * race condition along with SSR block allocation.
		 */
		if ((gc_type == BG_GC && has_not_enough_free_secs(sbi, 0, 0)) ||
			(!force_migrate && get_valid_blocks(sbi, segno, true) ==
							BLKS_PER_SEC(sbi)))
			return submitted;

Thanks,

> 
>>
>> 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)