linux-kernel - Re: [PATCH] mm/page-writeback: Consolidate wb_thresh bumping logic into __wb_calc

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Message-ID: <64a44636-16ec-4a10-aeb6-e327b7f989c2@roeck-us.net>
Date: Tue, 14 Jan 2025 07:01:08 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Jan Kara <jack@...e.cz>
Cc: Jim Zhao <jimzhao.ai@...il.com>, akpm@...ux-foundation.org,
 willy@...radead.org, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm/page-writeback: Consolidate wb_thresh bumping logic
 into __wb_calc_thresh

On 1/14/25 05:19, Jan Kara wrote:
> On Mon 13-01-25 15:05:25, Guenter Roeck wrote:
>> Hi,
>>
>> On Thu, Nov 21, 2024 at 06:05:39PM +0800, Jim Zhao wrote:
>>> Address the feedback from "mm/page-writeback: raise wb_thresh to prevent
>>> write blocking with strictlimit"(39ac99852fca98ca44d52716d792dfaf24981f53).
>>> The wb_thresh bumping logic is scattered across wb_position_ratio,
>>> __wb_calc_thresh, and wb_update_dirty_ratelimit. For consistency,
>>> consolidate all wb_thresh bumping logic into __wb_calc_thresh.
>>>
>>> Reviewed-by: Jan Kara <jack@...e.cz>
>>> Signed-off-by: Jim Zhao <jimzhao.ai@...il.com>
>>
>> This patch triggers a boot failure with one of my 'sheb' boot tests.
>> It is seen when trying to boot from flash (mtd). The log says
>>
>> ...
>> Starting network: 8139cp 0000:00:02.0 eth0: link down
>> udhcpc: started, v1.33.0
>> EXT2-fs (mtdblock3): error: ext2_check_folio: bad entry in directory #363: : directory entry across blocks - offset=0, inode=27393, rec_len=3072, name_len=2
>> udhcpc: sending discover
>> udhcpc: sending discover
>> udhcpc: sending discover
>> EXT2-fs (mtdblock3): error: ext2_check_folio: bad entry in directory #363: : directory entry across blocks - offset=0, inode=27393, rec_len=3072, name_len=2
> 
> Thanks for report! Uh, I have to say I'm very confused by this. It is clear
> than when ext2 detects the directory corruption (we fail checking directory
> inode 363 which is likely /etc/init.d/), the boot fails in interesting
> ways. What is unclear is how the commit can possibly cause ext2 directory
> corruption.  If you didn't verify reverting the commit fixes the issue, I'd
> be suspecting bad bisection but that obviously isn't the case :-)
> 
> Ext2 is storing directory data in the page cache so at least it uses the
> subsystem which the patch impacts but how writeback throttling can cause
> ext2 directory corruption is beyond me. BTW, do you recreate the root
> filesystem before each boot? How exactly?
> 

I use pre-built root file systems. For sheb, they are at
https://github.com/groeck/linux-build-test/tree/master/rootfs/sheb

I don't think this is related to ext2 itself. Booting an ext2 image from
ata/ide drive works.

Guenter