linux-kernel - Re: [PATCH v2] mm/ksm: fix flag-dropping behavior in ksm

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Message-ID: <20251001090755.GA66706@dev-dsk-acsjakub-1b-6f9934e2.eu-west-1.amazon.com>
Date: Wed, 1 Oct 2025 09:07:55 +0000
From: Jakub Acs <acsjakub@...zon.de>
To: David Hildenbrand <david@...hat.com>
CC: <linux-mm@...ck.org>, Andrew Morton <akpm@...ux-foundation.org>, Xu Xin
	<xu.xin16@....com.cn>, Chengming Zhou <chengming.zhou@...ux.dev>, Peter Xu
	<peterx@...hat.com>, Axel Rasmussen <axelrasmussen@...gle.com>,
	<linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>
Subject: Re: [PATCH v2] mm/ksm: fix flag-dropping behavior in ksm_madvise

On Tue, Sep 30, 2025 at 05:32:25PM +0200, David Hildenbrand wrote:
> If we want a smaller patch for easier backporting, we could split
> off the VM_MERGEABLE change into a separate patch and do all the
> other ones for consistency in another
> 
> Reading what we do VM_HIGH_ARCH_BIT_* , we use BIT(), which does
> 
> 	#define BIT(nr)		(UL(1) << (nr))
> 
> So likely we should just clean it all up an use e.g.,
> 
> #define VM_NONE		0
> #define VM_READ		BIT(0)
> #define VM_WRITE	BIT(1)
> 
> etc.
> 
> So likely it's best to do in a first fix
> 	#define VM_MERGEABLE	BIT(31)
> 
> And in a follow-up cleanup patch convert all the other ones.

Sent in v3: 
https://lore.kernel.org/all/20251001090353.57523-1-acsjakub@amazon.de/

It's the first time I sent a series, please let me know if I did
something wrong :)

> 
> Sorry for not thinking about BIT() earlier
> 

No worries :)

Kind Regards,
Jakub



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