linux-kernel - Re: [PATCH v2] mm: count zeromap read and set for swapout and swapin

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Message-ID: <942f8355-4b23-4fd9-b00e-1121552d89ee@redhat.com>
Date: Tue, 5 Nov 2024 09:23:43 +0100
From: David Hildenbrand <david@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Barry Song <21cnbao@...il.com>, Usama Arif <usamaarif642@...il.com>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Barry Song <v-songbaohua@...o.com>, Chengming Zhou
 <chengming.zhou@...ux.dev>, Yosry Ahmed <yosryahmed@...gle.com>,
 Nhat Pham <nphamcs@...il.com>, Johannes Weiner <hannes@...xchg.org>,
 Hugh Dickins <hughd@...gle.com>, Matthew Wilcox <willy@...radead.org>,
 Shakeel Butt <shakeel.butt@...ux.dev>, Andi Kleen <ak@...ux.intel.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>, Chris Li <chrisl@...nel.org>,
 "Huang, Ying" <ying.huang@...el.com>, Kairui Song <kasong@...cent.com>,
 Ryan Roberts <ryan.roberts@....com>
Subject: Re: [PATCH v2] mm: count zeromap read and set for swapout and swapin

On 05.11.24 04:40, Andrew Morton wrote:
> On Mon, 4 Nov 2024 13:32:55 +0100 David Hildenbrand <david@...hat.com> wrote:
> 
>>> As mentioned above, this isn't about fixing a bug; it's simply to ensure
>>> that swap-related metrics don't disappear.
>>
>> Documentation/process/submitting-patches.rst:
>>
>> "A Fixes: tag indicates that the patch fixes an issue in a previous
>> commit. It is used to make it easy to determine where a bug originated,
>> which can help review a bug fix."
>>
>> If there is no BUG, I'm afraid you are abusing that tag.
> 
> I think the abuse is reasonable.  We have no Should-be-included-with:.

A "Belongs-to:" might make sense, for this kind of stuff that is still 
only in an RFC. Or we update the doc to explicitly spell out this 
special case of using "Fixes" to sort out something into the RC.

Because if this would be already in a released kernel, it would get a 
bit trickier: stable rules explicitly spell out "fix a real bug".

> 
> 0ca0c24e3211 is only in 6.12-rcX so this is the time to make
> userspace-visible tweaks, so the 6.12 interfaces are the same as the
> 6.13+ interfaces (which is what I think is happening here?)
 > > And including the Fixes in this patch might be useful to someone who is
> backporting 0ca0c24e3211 into some earlier kernel for their own
> purposes.

Just to be clear: adding new counters would hardly be fixing existing 
tools that perform calculations based on existing counters. So we are 
already changing the "userspace-visible" portion in some way, and I have 
no idea what in vmstat we consider "stable".

But I still don't think it's all that big of a deal except in some 
handcrafted scenarios hardly anybody cares about; the cover letter is 
also pretty clear on that.

So I'll shut up now and let people figure out the naming first, and if a 
new counter is required at all :)

-- 
Cheers,

David / dhildenb