linux-kernel - Re: [PATCH V2] f2fs: fix to avoid use GC_AT when setting gc_mode as GC_URGENT_LOW or GC_URGENT

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Message-ID: <7d68560a-19ea-455c-ba23-1dda32ed4d15@kernel.org>
Date: Mon, 28 Oct 2024 17:33:55 +0800
From: Chao Yu <chao@...nel.org>
To: Zhiguo Niu <zhiguo.niu@...soc.com>, jaegeuk@...nel.org
Cc: Chao Yu <chao@...nel.org>, linux-f2fs-devel@...ts.sourceforge.net,
 linux-kernel@...r.kernel.org, niuzhiguo84@...il.com, ke.wang@...soc.com,
 Hao_hao.Wang@...soc.com
Subject: Re: [PATCH V2] f2fs: fix to avoid use GC_AT when setting gc_mode as
 GC_URGENT_LOW or GC_URGENT_MID

On 2024/10/23 11:08, Zhiguo Niu wrote:
> If gc_mode is set to GC_URGENT_LOW or GC_URGENT_MID, cost benefit GC
> approach should be used, but if ATGC is enabled at the same time,
> Age-threshold approach will be selected, which can only do amount of
> GC and it is much less than the numbers of CB approach.

The code looks fine to me, there is one more thing, can you please update
description of gc_urgent in sysfs-fs-f2fs? so it can describe explicitly
that configuring gc_urgent to low or mid will setup GC_CB GC policy which
will override GC_AT.

Thanks,

> 
> some traces:
>    f2fs_gc-254:48-396     [007] ..... 2311600.684028: f2fs_gc_begin: dev = (254,48), gc_type = Background GC, no_background_GC = 0, nr_free_secs = 0, nodes = 1053, dents = 2, imeta = 18, free_sec:44898, free_seg:44898, rsv_seg:239, prefree_seg:0
>    f2fs_gc-254:48-396     [007] ..... 2311600.684527: f2fs_get_victim: dev = (254,48), type = No TYPE, policy = (Background GC, LFS-mode, Age-threshold), victim = 10, cost = 4294364975, ofs_unit = 1, pre_victim_secno = -1, prefree = 0, free = 44898
>    f2fs_gc-254:48-396     [007] ..... 2311600.714835: f2fs_gc_end: dev = (254,48), ret = 0, seg_freed = 0, sec_freed = 0, nodes = 1562, dents = 2, imeta = 18, free_sec:44898, free_seg:44898, rsv_seg:239, prefree_seg:0
>    f2fs_gc-254:48-396     [007] ..... 2311600.714843: f2fs_background_gc: dev = (254,48), wait_ms = 50, prefree = 0, free = 44898
>    f2fs_gc-254:48-396     [007] ..... 2311600.771785: f2fs_gc_begin: dev = (254,48), gc_type = Background GC, no_background_GC = 0, nr_free_secs = 0, nodes = 1562, dents = 2, imeta = 18, free_sec:44898, free_seg:44898, rsv_seg:239, prefree_seg:
>    f2fs_gc-254:48-396     [007] ..... 2311600.772275: f2fs_gc_end: dev = (254,48), ret = -61, seg_freed = 0, sec_freed = 0, nodes = 1562, dents = 2, imeta = 18, free_sec:44898, free_seg:44898, rsv_seg:239, prefree_seg:0
> 
> Fixes: 0e5e81114de1 ("f2fs: add GC_URGENT_LOW mode in gc_urgent")
> Fixes: d98af5f45520 ("f2fs: introduce gc_urgent_mid mode")
> Signed-off-by: Zhiguo Niu <zhiguo.niu@...soc.com>
> ---
> v2: make GC_URGENT_LOW also use CB approach
> ---
>   fs/f2fs/gc.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index e40bdd1..3e1b6d2 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -257,6 +257,8 @@ static int select_gc_type(struct f2fs_sb_info *sbi, int gc_type)
>   
>   	switch (sbi->gc_mode) {
>   	case GC_IDLE_CB:
> +	case GC_URGENT_LOW:
> +	case GC_URGENT_MID:
>   		gc_mode = GC_CB;
>   		break;
>   	case GC_IDLE_GREEDY: