linux-kernel - Re: [PATCH v2 0/5] madvise cleanup

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Message-Id: <20250620172108.95944-1-sj@kernel.org>
Date: Fri, 20 Jun 2025 10:21:08 -0700
From: SeongJae Park <sj@...nel.org>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: SeongJae Park <sj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>,
	Zi Yan <ziy@...dia.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	Nico Pache <npache@...hat.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Dev Jain <dev.jain@....com>,
	Barry Song <baohua@...nel.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Jann Horn <jannh@...gle.com>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Lance Yang <ioworker0@...il.com>,
	Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH v2 0/5] madvise cleanup

On Fri, 20 Jun 2025 16:33:00 +0100 Lorenzo Stoakes <lorenzo.stoakes@...cle.com> wrote:

> This is a series of patches that helps address a number of historic
> problems in the madvise() implementation:
> 
> * Eliminate the visitor pattern and having the code which is implemented
>   for both the anon_vma_name implementation and ordinary madvise()
>   operations use the same madvise_vma_behavior() implementation.
> 
> * Thread state through the madvise_behavior state object - this object,
>   very usefully introduced by SJ, is already used to transmit state through
>   operations. This series extends this by having all madvise() operations
>   use this, including anon_vma_name.
> 
> * Thread range, VMA state through madvise_behavior - This helps avoid a lot
>   of the confusing code around range and VMA state and again keeps things
>   consistent and with a single 'source of truth'.
> 
> * Addressing the very strange behaviour around the passed around struct
>   vm_area_struct **prev pointer - all read-only users do absolutely nothing
>   with the prev pointer. The only function that uses it is
>   madvise_update_vma(), and in all cases prev is always reset to
>   VMA.
> 
>   Fix this by no longer having aything but madvise_update_vma() reference
>   prev, and having madvise_walk_vmas() update prev in each
>   instance. Additionally make it clear that the meaningful change in vma
>   state is when madvise_update_vma() potentially merges a VMA, so
>   explicitly retrieve the VMA in this case.
> 
> * Update and clarify the madvise_walk_vmas() function - this is a source of
>   a great deal of confusion, so simplify, stop using prev = NULL to signify
>   that the mmap lock has been dropped (!) and make that explicit, and add
>   some comments to explain what's going on.
> 
> v2:
> * Propagated tags (thanks everyone!)
> * Don't separate out __MADV_SET_ANON_VMA_NAME and __MADV_SET_CLEAR_VMA_NAME,

FWIW.  If this cover letter is added to the first patch, like Andrew usually
does, as-is, checkpatch.pl may warn like below.

   WARNING: Prefer a maximum 75 chars per line (possible unwrapped commit description?)

Obviously no real problem and I don't really care.  I just found this since my
tool (hkml) runs checkpatch.pl after adding the cover letter to the first
patch, and hence this is just FWIW.


Thanks,
SJ

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