Re: [PATCH] f2fs: fix FG GC failure when file in victim is pinned
From: Chao Yu
Date: Thu Jun 25 2026 - 03:09:51 EST
On 6/22/26 18:40, Jiucheng Xu wrote:
>
> On 6/22/2026 9:46 AM, Chao Yu wrote:
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>>
>> [ EXTERNAL EMAIL ]
>>
>> On 6/20/26 17:34, Jiucheng Xu via B4 Relay wrote:
>>> From: Jiucheng Xu <jiucheng.xu@xxxxxxxxxxx>
>>>
>>> When continuous write operations occur in the system, BG GC fails to
>>> work. This leads to large dirty_segments and small free_segments. If
>>> fallocate() is performed on a pinned file with the allocated space
>>> exceeding the free_segment, FG_GC reclamation fails.
>>>
>>> The reason is that the file corresponding to the block in the victim is
>>> pinned, causing gc_data_segment() to fail. Since the condition sec_freed
>>
>> Jiucheng,
>>
>> pinned file should be aligned to section size, why there is fragmented blocks
>> of pinfile locates in dirty sections?
>>
>>> < gc_control->nr_free_secs isn't satisfied, GC stops, resulting in the
>>> failure of f2fs_fallocate() allocation.
>>>
>>> Setting gc_control->nr_free_secs = 1 make FG GC continue searching
>>> for new victim.
>>
>> Maybe we can try this instead of changing f2fs_expand_inode_data() logic:
>> 1. call fggc via ioctl or trigger urgent gc via sysfs
>> 2. fallocate on pinfile, goto 1) if it failed
>>
>> But, anyway, I suspect it's risk, if there is no normal dirty section,
>> FGGC will try to call f2fs_unpin_all_sections(), then migrate dirty section
>> which has pinned blocks, that will cause more damage.
>>
>> Can you please figure out why pinfile is fragmented first...
>
> Hi Chao,
>
> Thanks for your feedback. I just do a test to simulate the Android OTA createCowImage failed when dirty_segments is too large.
>
> Simple reproduction steps:
> 1. In my case, dirty_segments=969, free_segments=96, free space = 1.7G, section:segment = 1:1
> 2. touch a.bin
> 3. f2fs_io pinfile set a.bin
> 4. fallocate -l 1.5G a.bin
>
> And f2fs_fallocate() returns -11.
>
> Although the urgent mode work fine, but it is not very convenient to control since AOPS has a great deal of code that calls fallocate.
>
> I have tried 5 times to fallocate(), but GC always selects the same victim segno. So I think it is an issue.
>
>
> The trace:
> f2fs_get_victim: dev = (254,0), type = No TYPE, policy = (Foreground GC, LFS-mode, Greedy), victim = 624, cost = 19...
>
> f2fs_gc_end: dev = (254,0), ret = 0, seg_freed = 0, sec_freed = 0, nodes = 117, dents = 0, imeta = 98, free_sec:50, free_seg:50, rsv_seg:47, prefree_seg:47
>
>
> I dump the failed victim segno, block offset in segment and related inode ino:
> do_garbage_collect: ino=33902 segno=624 off=132
>
> The dump of pinfile 33902 info:
> main_blkaddr [0x 2600 : 9728]
> i_inline [0x 61 : 97]
> inline shows the file is pinned (0x60)
> i_addr[0x9] [0x 2f7b2 : 194482]
> i_addr[0xa] [0x 2f7b3 : 194483]
> i_addr[0xb] [0x 2f7b4 : 194484]
> ...
> i_addr[0x1d] [0x 2f7c6 : 194502]
> i_addr[0x1e] [0x 465af : 288175]
> i_addr[0x1f] [0x 465b0 : 288176]
> ...
> i_addr[0x21] [0x 465b2 : 288178]
> i_addr[0x22] [0x 5046d : 328813]
> i_addr[0x23] [0x 5046e : 328814]
> i_addr[0x24] [0x 505b6 : 329142]
> i_addr[0x25] [0x 505b7 : 329143]
> i_addr[0x26] [0x 505b8 : 329144]
> i_addr[0x27] [0x 50684 : 329348]
> i_addr[0x28] [0x 50685 : 329349]
>
> The file is created by logcat,and looks like indeed fragmented.
>
> Calculate the block address:
> 624 * 512 + 132 + 9728(main_blkaddr) = 329348
>
> So the i_addr[0x27] = 329348 is the failed block.
>
> Regarding "why the pinfile is fragmented" you said, we use v5.15 + android U. Is it that v5.15 lacks some patches for special handling of pinfiles?
Ah, I think you can unpin log file created by logcat, the flag is added
in aosp/1014260 to avoid fragmentation in filesystem (), but it's gone in
aosp/43c6d76a
Thanks,
>
> Thanks,
>
>
>>
>> Thanks,
>>
>>>
>>> Signed-off-by: Jiucheng Xu <jiucheng.xu@xxxxxxxxxxx>
>>> ---
>>> 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 8acdd94272a0ced448e0ba21635d702cfec10682..3e49a73bbf3a184a314e97bff9509a66c27eac00 100644
>>> --- a/fs/f2fs/file.c
>>> +++ b/fs/f2fs/file.c
>>> @@ -1883,7 +1883,7 @@ static int f2fs_expand_inode_data(struct inode *inode, loff_t offset,
>>> .init_gc_type = FG_GC,
>>> .should_migrate_blocks = false,
>>> .err_gc_skipped = true,
>>> - .nr_free_secs = 0 };
>>> + .nr_free_secs = 1 };
>>> pgoff_t pg_start, pg_end;
>>> loff_t new_size;
>>> loff_t off_end;
>>>
>>> ---
>>> base-commit: b51f606aa323d553d786ed681a213f134dc688d6
>>> change-id: 20260620-origin-dev-99cdccc83800
>>>
>>> Best regards,
>>
>