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Message-ID: <d258ab6d-a97a-4232-bf90-5afedd5cccb2@kernel.org>
Date: Mon, 28 Jul 2025 15:38:25 +0800
From: Chao Yu <chao@...nel.org>
To: Qi Han <hanqi@...o.com>, jaegeuk@...nel.org
Cc: chao@...nel.org, axboe@...nel.dk, linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] f2fs: f2fs supports uncached buffered I/O read
On 7/25/25 15:53, Qi Han wrote:
> Jens has already completed the development of uncached buffered I/O
> in git [1], and in f2fs, uncached buffered I/O read can be enabled
> simply by setting the FOP_DONTCACHE flag in f2fs_file_operations.
IIUC, we may suffer lock issue when we call pwritev(.. ,RWF_DONTCACHE)?
as Jen mentioned in below path, right?
soft-irq
- folio_end_writeback()
- filemap_end_dropbehind_write()
- filemap_end_dropbehind()
- folio_unmap_invalidate()
- lock i_lock
Thanks,
>
> I have been testing a use case locally, which aligns with Jens' test
> case [2]. In the read scenario, using uncached buffer I/O results in
> more stable read performance and a lower load on the background memory
> reclaim thread (kswapd). So let's enable uncached buffer I/O reads on
> F2FS.
>
> Read test data without using uncached buffer I/O:
> reading bs 32768, uncached 0
> 1s: 1856MB/sec, MB=1856
> 2s: 1907MB/sec, MB=3763
> 3s: 1830MB/sec, MB=5594
> 4s: 1745MB/sec, MB=7333
> 5s: 1829MB/sec, MB=9162
> 6s: 1903MB/sec, MB=11075
> 7s: 1878MB/sec, MB=12942
> 8s: 1763MB/sec, MB=14718
> 9s: 1845MB/sec, MB=16549
> 10s: 1915MB/sec, MB=18481
> 11s: 1831MB/sec, MB=20295
> 12s: 1750MB/sec, MB=22066
> 13s: 1787MB/sec, MB=23832
> 14s: 1913MB/sec, MB=25769
> 15s: 1898MB/sec, MB=27668
> 16s: 1795MB/sec, MB=29436
> 17s: 1812MB/sec, MB=31248
> 18s: 1890MB/sec, MB=33139
> 19s: 1880MB/sec, MB=35020
> 20s: 1754MB/sec, MB=36810
>
> 08:36:26 UID PID %usr %system %guest %wait %CPU CPU Command
> 08:36:27 0 93 0.00 0.00 0.00 0.00 0.00 7 kswapd0
> 08:36:28 0 93 0.00 0.00 0.00 0.00 0.00 7 kswapd0
> 08:36:29 0 93 0.00 0.00 0.00 0.00 0.00 7 kswapd0
> 08:36:30 0 93 0.00 56.00 0.00 0.00 56.00 7 kswapd0
> 08:36:31 0 93 0.00 73.00 0.00 0.00 73.00 7 kswapd0
> 08:36:32 0 93 0.00 83.00 0.00 0.00 83.00 7 kswapd0
> 08:36:33 0 93 0.00 75.00 0.00 0.00 75.00 7 kswapd0
> 08:36:34 0 93 0.00 81.00 0.00 0.00 81.00 7 kswapd0
> 08:36:35 0 93 0.00 54.00 0.00 1.00 54.00 2 kswapd0
> 08:36:36 0 93 0.00 61.00 0.00 0.00 61.00 0 kswapd0
> 08:36:37 0 93 0.00 68.00 0.00 0.00 68.00 7 kswapd0
> 08:36:38 0 93 0.00 53.00 0.00 0.00 53.00 2 kswapd0
> 08:36:39 0 93 0.00 82.00 0.00 0.00 82.00 7 kswapd0
> 08:36:40 0 93 0.00 77.00 0.00 0.00 77.00 1 kswapd0
> 08:36:41 0 93 0.00 74.00 0.00 1.00 74.00 7 kswapd0
> 08:36:42 0 93 0.00 71.00 0.00 0.00 71.00 7 kswapd0
> 08:36:43 0 93 0.00 78.00 0.00 0.00 78.00 7 kswapd0
> 08:36:44 0 93 0.00 85.00 0.00 0.00 85.00 7 kswapd0
> 08:36:45 0 93 0.00 83.00 0.00 0.00 83.00 7 kswapd0
> 08:36:46 0 93 0.00 70.00 0.00 0.00 70.00 7 kswapd0
> 08:36:47 0 93 0.00 78.00 0.00 1.00 78.00 2 kswapd0
> 08:36:48 0 93 0.00 81.00 0.00 0.00 81.00 3 kswapd0
> 08:36:49 0 93 0.00 54.00 0.00 0.00 54.00 7 kswapd0
> 08:36:50 0 93 0.00 76.00 0.00 0.00 76.00 1 kswapd0
> 08:36:51 0 93 0.00 75.00 0.00 0.00 75.00 0 kswapd0
> 08:36:52 0 93 0.00 73.00 0.00 0.00 73.00 7 kswapd0
> 08:36:53 0 93 0.00 61.00 0.00 1.00 61.00 7 kswapd0
> 08:36:54 0 93 0.00 80.00 0.00 0.00 80.00 7 kswapd0
> 08:36:55 0 93 0.00 64.00 0.00 0.00 64.00 7 kswapd0
> 08:36:56 0 93 0.00 56.00 0.00 0.00 56.00 7 kswapd0
> 08:36:57 0 93 0.00 26.00 0.00 0.00 26.00 2 kswapd0
> 08:36:58 0 93 0.00 24.00 0.00 1.00 24.00 3 kswapd0
> 08:36:59 0 93 0.00 22.00 0.00 1.00 22.00 3 kswapd0
> 08:37:00 0 93 0.00 15.84 0.00 0.00 15.84 3 kswapd0
> 08:37:01 0 93 0.00 0.00 0.00 0.00 0.00 3 kswapd0
> 08:37:02 0 93 0.00 0.00 0.00 0.00 0.00 3 kswapd0
>
> Read test data after using uncached buffer I/O:
> reading bs 32768, uncached 1
> 1s: 1863MB/sec, MB=1863
> 2s: 1903MB/sec, MB=3766
> 3s: 1860MB/sec, MB=5627
> 4s: 1864MB/sec, MB=7491
> 5s: 1860MB/sec, MB=9352
> 6s: 1854MB/sec, MB=11206
> 7s: 1874MB/sec, MB=13081
> 8s: 1874MB/sec, MB=14943
> 9s: 1840MB/sec, MB=16798
> 10s: 1849MB/sec, MB=18647
> 11s: 1863MB/sec, MB=20511
> 12s: 1798MB/sec, MB=22310
> 13s: 1897MB/sec, MB=24207
> 14s: 1817MB/sec, MB=26025
> 15s: 1893MB/sec, MB=27918
> 16s: 1917MB/sec, MB=29836
> 17s: 1863MB/sec, MB=31699
> 18s: 1904MB/sec, MB=33604
> 19s: 1894MB/sec, MB=35499
> 20s: 1907MB/sec, MB=37407
>
> 08:38:00 UID PID %usr %system %guest %wait %CPU CPU Command
> 08:38:01 0 93 0.00 0.00 0.00 0.00 0.00 4 kswapd0
> 08:38:02 0 93 0.00 0.00 0.00 0.00 0.00 4 kswapd0
> 08:38:03 0 93 0.00 0.00 0.00 0.00 0.00 4 kswapd0
> 08:38:04 0 93 0.00 0.00 0.00 0.00 0.00 4 kswapd0
> 08:38:05 0 93 0.00 0.00 0.00 0.00 0.00 4 kswapd0
> 08:38:06 0 93 0.00 1.00 0.00 1.00 1.00 0 kswapd0
> 08:38:07 0 93 0.00 0.00 0.00 0.00 0.00 0 kswapd0
> 08:38:08 0 93 0.00 0.00 0.00 0.00 0.00 0 kswapd0
> 08:38:09 0 93 0.00 1.00 0.00 0.00 1.00 1 kswapd0
> 08:38:10 0 93 0.00 0.00 0.00 0.00 0.00 1 kswapd0
> 08:38:11 0 93 0.00 0.00 0.00 0.00 0.00 1 kswapd0
> 08:38:12 0 93 0.00 0.00 0.00 0.00 0.00 1 kswapd0
> 08:38:13 0 93 0.00 0.00 0.00 0.00 0.00 1 kswapd0
> 08:38:14 0 93 0.00 0.00 0.00 0.00 0.00 1 kswapd0
> 08:38:15 0 93 0.00 3.00 0.00 0.00 3.00 0 kswapd0
> 08:38:16 0 93 0.00 0.00 0.00 0.00 0.00 0 kswapd0
> 08:38:17 0 93 0.00 0.00 0.00 0.00 0.00 0 kswapd0
> 08:38:18 0 93 0.00 0.00 0.00 0.00 0.00 0 kswapd0
> 08:38:19 0 93 0.00 0.00 0.00 0.00 0.00 0 kswapd0
> 08:38:20 0 93 0.00 0.00 0.00 0.00 0.00 0 kswapd0
> 08:38:21 0 93 0.00 0.00 0.00 0.00 0.00 0 kswapd0
> 08:38:22 0 93 0.00 0.00 0.00 0.00 0.00 0 kswapd0
> 08:38:23 0 93 0.00 3.00 0.00 0.00 3.00 4 kswapd0
> 08:38:24 0 93 0.00 0.00 0.00 0.00 0.00 4 kswapd0
> 08:38:25 0 93 0.00 0.00 0.00 0.00 0.00 4 kswapd0
> 08:38:26 0 93 0.00 4.00 0.00 0.00 4.00 3 kswapd0
> 08:38:27 0 93 0.00 0.00 0.00 0.00 0.00 3 kswapd0
> 08:38:28 0 93 0.00 0.00 0.00 0.00 0.00 3 kswapd0
> 08:38:29 0 93 0.00 0.00 0.00 0.00 0.00 3 kswapd0
> 08:38:30 0 93 0.00 0.00 0.00 0.00 0.00 3 kswapd0
> 08:38:31 0 93 0.00 0.00 0.00 0.00 0.00 3 kswapd0
> 08:38:32 0 93 0.00 0.00 0.00 0.00 0.00 3 kswapd0
> 08:38:33 0 93 0.00 0.00 0.00 0.00 0.00 3 kswapd0
>
> [1]
> https://lore.kernel.org/all/20241220154831.1086649-10-axboe@kernel.dk/T/#m58520a94b46f543d82db3711453dfc7bb594b2b0
>
> [2]
> https://pastebin.com/u8eCBzB5
>
> Signed-off-by: Qi Han <hanqi@...o.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 696131e655ed..d8da1fc2febf 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -5425,5 +5425,5 @@ const struct file_operations f2fs_file_operations = {
> .splice_read = f2fs_file_splice_read,
> .splice_write = iter_file_splice_write,
> .fadvise = f2fs_file_fadvise,
> - .fop_flags = FOP_BUFFER_RASYNC,
> + .fop_flags = FOP_BUFFER_RASYNC | FOP_DONTCACHE,
> };
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