linux-kernel - Re: ext4 writeback performance issue in 6.12

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Message-ID: <20251009175254.d6djmzn3vk726pao@matt-Precision-5490>
Date: Thu, 9 Oct 2025 18:52:54 +0100
From: Matt Fleming <matt@...dmodwrite.com>
To: Theodore Ts'o <tytso@....edu>
Cc: adilger.kernel@...ger.ca, jack@...e.cz, kernel-team@...udflare.com,
	libaokun1@...wei.com, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	willy@...radead.org
Subject: Re: ext4 writeback performance issue in 6.12

On Thu, Oct 09, 2025 at 11:22:59AM +0100, Matt Fleming wrote:
> 
> Thanks Ted. I'm going to try disabling the stripe parameter now. I'll report
> back shortly.

Initial results look very good. No blocked tasks so far and the mb
allocator latency is much improved.

mfleming@...e:~$ sudo perf ftrace latency -b  -a -T ext4_mb_regular_allocator -- sleep 10
#   DURATION     |      COUNT | GRAPH                                          |
     0 - 1    us |          0 |                                                |
     1 - 2    us |          0 |                                                |
     2 - 4    us |         41 |                                                |
     4 - 8    us |        499 | ###########                                    |
     8 - 16   us |        246 | #####                                          |
    16 - 32   us |        126 | ##                                             |
    32 - 64   us |        103 | ##                                             |
    64 - 128  us |         74 | #                                              |
   128 - 256  us |        109 | ##                                             |
   256 - 512  us |        293 | ######                                         |
   512 - 1024 us |        448 | ##########                                     |
     1 - 2    ms |         36 |                                                |
     2 - 4    ms |         11 |                                                |
     4 - 8    ms |          1 |                                                |
     8 - 16   ms |          0 |                                                |
    16 - 32   ms |          0 |                                                |
    32 - 64   ms |          0 |                                                |
    64 - 128  ms |          0 |                                                |
   128 - 256  ms |          0 |                                                |
   256 - 512  ms |          0 |                                                |
   512 - 1024 ms |          0 |                                                |
     1 - ...   s |          0 |                                                |

Thanks,
Matt