linux-kernel - Re: [PATCH 0/2] dm-pcache: fix metadata indexing and persistence issues

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Message-ID: <19aedc9220c.286fe1e31299075.4407856642004547155@linux.beauty>
Date: Fri, 05 Dec 2025 17:12:53 +0800
From: Li Chen <me@...ux.beauty>
To: "Dongsheng Yang" <dongsheng.yang@...ux.dev>
Cc: "dm-devel" <dm-devel@...ts.linux.dev>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	"Zheng Gu" <cengku@...il.com>
Subject: Re: [PATCH 0/2] dm-pcache: fix metadata indexing and persistence
 issues

Hi Dongsheng,

 ---- On Thu, 04 Dec 2025 09:38:17 +0800  Dongsheng Yang <dongsheng.yang@...ux.dev> wrote --- 
 > 
 > 在 12/4/2025 7:38 AM, Dongsheng Yang 写道:
 > >
 > > 在 12/3/2025 1:56 PM, Dongsheng Yang 写道:
 > >> Hi,
 > >>
 > >>     Thanx for your patches, there are some comments inline.
 > >>
 > >> According to these comments, I propose an update base on your patch 
 > >> as [1].
 > >>
 > >> BTW, I added a test case for this problem in dtg-tests:
 > >>
 > >> https://github.com/DataTravelGuide/dtg-tests/blob/main/pcache.py.data/pcache_misc_tests/case21_gc_percent_persistence_after_recreate.sh 
 > >>
 > >>
 > >> It update gc_percent online and recreate pcache device and check 
 > >> gc_percen
 > >>
 > >>
 > >> [1]:
 > >
 > >
 > > ->info_index means next slot to write, so advancing it at init stage 
 > > is correct
 > 
 > 
 > We need to think more thoroughly about the usage of the slot index. In 
 > my original design, all slot indices represent the “current slot”. So at 
 > initialization it is 0; if loading, we simply point it to the loaded 
 > slot; and on write we advance afterwards. However, the problem now is 
 > that in all write functions, they first write to the current slot, then 
 > advance.
 > 
 > Therefore I believe we should clarify that the meaning of the slot index 
 > is “the current slot,” and stick to the original design. We only need to 
 > modify the write functions: first perform the advance, and then write 
 > into the correct slot.
 
Sounds good, thanks.

Regards,

Li