linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: continue to allocate pinned section when gc happens EAGAIN

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Message-ID: <f1b9209e-c2fb-4a53-8d15-a3e42dea8bca@kernel.org>
Date: Thu, 12 Jun 2025 16:31:09 +0800
From: Chao Yu <chao@...nel.org>
To: wangzijie <wangzijie1@...or.com>, jaegeuk@...nel.org
Cc: chao@...nel.org, bo.wu@...o.com, linux-f2fs-devel@...ts.sourceforge.net,
 linux-kernel@...r.kernel.org
Subject: Re: [f2fs-dev] [PATCH] f2fs: continue to allocate pinned section when
 gc happens EAGAIN

On 6/12/25 11:27, wangzijie wrote:
> Wu Bo once mentioned a fallocate fail scenario in this link[1].
> After commit 3fdd89b452c2("f2fs: prevent writing without fallocate()
> for pinned files"), we cannot directly generate 4K size file and
> pin it, but we can still generate non-segment aligned pinned file:
> 
> touch test_file
> ./f2fs_io pinfile set test_file
> ./f2fs_io fallocate 0 0 8192 test_file
> truncate -s 4096 test_file

Well, shouldn't we avoid such case by adding check condition in setattr?

> 
> By doing this, pin+fallocate failure(gc happens EAGAIN but f2fs shows
> enough spare space) may occurs.
> 
> From message in commit 2e42b7f817ac("f2fs: stop allocating pinned sections
> if EAGAIN happens"), gc EAGAIN doesn't guarantee a free section, so we stop
> allocating. But after commit 48ea8b200414 ("f2fs: fix to avoid panic once 
> fallocation fails for pinfile"), we have a way to avoid panic caused by
> concurrent pinfile allocation run out of free section, so I think that we 
> can continue to allocate pinned section when gc happens EAGAIN. Even if we
> don't have free section, f2fs_allocate_pinning_section() can fail with ENOSPC.

What do you think of introduce /sys/fs/f2fs/<dev>/reserved_pin_section to
tune @needed parameter of has_not_enough_free_secs()? If we configure it
w/ zero, it can avoid f2fs_gc() before preallocation.

---
 fs/f2fs/f2fs.h  | 3 +++
 fs/f2fs/file.c  | 5 ++---
 fs/f2fs/super.c | 3 +++
 fs/f2fs/sysfs.c | 9 +++++++++
 4 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 785537576aa8..ffb15da570d7 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1731,6 +1731,9 @@ struct f2fs_sb_info {
 	/* for skip statistic */
 	unsigned long long skipped_gc_rwsem;		/* FG_GC only */

+	/* free sections reserved for pinned file */
+	unsigned int reserved_pin_section;
+
 	/* threshold for gc trials on pinned files */
 	unsigned short gc_pin_file_threshold;
 	struct f2fs_rwsem pin_sem;
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 696131e655ed..a909f79db178 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1887,9 +1887,8 @@ static int f2fs_expand_inode_data(struct inode *inode, loff_t offset,
 			}
 		}

-		if (has_not_enough_free_secs(sbi, 0, f2fs_sb_has_blkzoned(sbi) ?
-			ZONED_PIN_SEC_REQUIRED_COUNT :
-			GET_SEC_FROM_SEG(sbi, overprovision_segments(sbi)))) {
+		if (has_not_enough_free_secs(sbi, 0,
+				sbi->reserved_pin_section)) {
 			f2fs_down_write(&sbi->gc_lock);
 			stat_inc_gc_call_count(sbi, FOREGROUND);
 			err = f2fs_gc(sbi, &gc_control);
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 57adeff5ef25..48b97a95fd63 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -4975,6 +4975,9 @@ static int f2fs_fill_super(struct super_block *sb, struct fs_context *fc)
 	sbi->last_valid_block_count = sbi->total_valid_block_count;
 	sbi->reserved_blocks = 0;
 	sbi->current_reserved_blocks = 0;
+	sbi->reserved_pin_section = f2fs_sb_has_blkzoned(sbi) ?
+			ZONED_PIN_SEC_REQUIRED_COUNT :
+			GET_SEC_FROM_SEG(sbi, overprovision_segments(sbi));
 	limit_reserve_root(sbi);
 	adjust_unusable_cap_perc(sbi);

diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index 75134d69a0bd..51be7ffb38c5 100644
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -824,6 +824,13 @@ static ssize_t __sbi_store(struct f2fs_attr *a,
 		return count;
 	}

+	if (!strcmp(a->attr.name, "reserved_pin_section")) {
+		if (t > GET_SEC_FROM_SEG(sbi, overprovision_segments(sbi)))
+			return -EINVAL;
+		*ui = (unsigned int)t;
+		return count;
+	}
+
 	*ui = (unsigned int)t;

 	return count;
@@ -1130,6 +1137,7 @@ F2FS_SBI_GENERAL_RO_ATTR(unusable_blocks_per_sec);
 F2FS_SBI_GENERAL_RW_ATTR(blkzone_alloc_policy);
 #endif
 F2FS_SBI_GENERAL_RW_ATTR(carve_out);
+F2FS_SBI_GENERAL_RW_ATTR(reserved_pin_section);

 /* STAT_INFO ATTR */
 #ifdef CONFIG_F2FS_STAT_FS
@@ -1323,6 +1331,7 @@ static struct attribute *f2fs_attrs[] = {
 	ATTR_LIST(last_age_weight),
 	ATTR_LIST(max_read_extent_count),
 	ATTR_LIST(carve_out),
+	ATTR_LIST(reserved_pin_section),
 	NULL,
 };
 ATTRIBUTE_GROUPS(f2fs);
-- 
2.49.0


> 
> [1] https://lore.kernel.org/linux-f2fs-devel/20231030094024.263707-1-bo.wu@vivo.com/t/#u
> 
> Signed-off-by: wangzijie <wangzijie1@...or.com>
> ---
>  fs/f2fs/file.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index 6bd3de64f..05c80d2b5 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -1859,7 +1859,7 @@ static int f2fs_expand_inode_data(struct inode *inode, loff_t offset,
>  			f2fs_down_write(&sbi->gc_lock);
>  			stat_inc_gc_call_count(sbi, FOREGROUND);
>  			err = f2fs_gc(sbi, &gc_control);
> -			if (err && err != -ENODATA) {
> +			if (err && err != -ENODATA && err != -EAGAIN) {
>  				f2fs_up_write(&sbi->pin_sem);
>  				goto out_err;
>  			}