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Message-ID: <ab569309-f639-33af-ebb3-909a02158d02@kernel.org>
Date:   Thu, 12 May 2022 10:04:01 +0800
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Subject: Re: [f2fs-dev] [PATCH 4/5] f2fs: do not stop GC when requiring a free
 section
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To:     Jaegeuk Kim <jaegeuk@kernel.org>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net
References: <20220506232032.1264078-1-jaegeuk@kernel.org>
 <20220506232032.1264078-4-jaegeuk@kernel.org>
 <77e870dd-fd7a-f58e-79fb-d0e5b8fbfc16@kernel.org>
 <YnlHdgHix+3qlc1a@google.com>
 <42c23c83-1914-e8dd-c765-df3d6d872532@kernel.org>
 <Ynvoszmp7+64NdZg@google.com>
From:   Chao Yu <chao@kernel.org>
In-Reply-To: <Ynvoszmp7+64NdZg@google.com>
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On 2022/5/12 0:47, Jaegeuk Kim wrote:
>>>>> @@ -147,6 +147,7 @@ static int gc_thread_func(void *data)
>>>>>     		gc_control.init_gc_type = sync_mode ? FG_GC : BG_GC;
>>>>>     		gc_control.no_bg_gc = foreground;
>>>>> +		gc_control.nr_free_secs = foreground ? 1 : 0;

[snip]

> 
> I mean gc_control->nr_free_secs should be 0.

[snip]

>>>>> @@ -528,7 +528,8 @@ void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need)
>>>>>     				.init_gc_type = BG_GC,
>>>>>     				.no_bg_gc = true,
>>>>>     				.should_migrate_blocks = false,
>>>>> -				.err_gc_skipped = false };
>>>>> +				.err_gc_skipped = false,
>>>>> +				.nr_free_secs = 1 };

Oh, so, in above two paths, when .nr_free_secs is 1, no_bg_gc should be true
to keep skipping BG_GC flow.

How about adding a check condition in f2fs_gc() to avoid invalid argument
usage in future?

From: Chao Yu <chao@kernel.org>

---
  fs/f2fs/gc.c | 17 +++++++++++++----
  1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 385282017317..a98276fd3cc1 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -1799,10 +1799,19 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
  			gc_type = FG_GC;
  	}

-	/* f2fs_balance_fs doesn't need to do BG_GC in critical path. */
-	if (gc_type == BG_GC && gc_control->no_bg_gc) {
-		ret = -EINVAL;
-		goto stop;
+	if (gc_type == BG_GC) {
+		/* f2fs_balance_fs doesn't need to do BG_GC in critical path. */
+		if (gc_control->no_bg_gc) {
+			ret = -EINVAL;
+			goto stop;
+		}
+		/*
+		 * BG_GC never guarantee that blocks are migrated synchronously.
+		 */
+		if (gc_control->nr_free_secs) {
+			ret = -EINVAL;
+			goto stop;
+		}
  	}
  retry:
  	ret = __get_victim(sbi, &segno, gc_type);
-- 
2.25.1


Thanks,