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SubjectRe: [f2fs-dev] [PATCH 2/3] f2fs: run GCs synchronously given user requests
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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@kernel.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)

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