linux-kernel - Re: [PATCH v2 1/5] mm/madvise: remove the visitor pattern and thread anon

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Message-Id: <20250620171256.95735-1-sj@kernel.org>
Date: Fri, 20 Jun 2025 10:12:56 -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 1/5] mm/madvise: remove the visitor pattern and thread anon_vma state

On Fri, 20 Jun 2025 16:33:01 +0100 Lorenzo Stoakes <lorenzo.stoakes@...cle.com> wrote:

> Now we have the madvise_behavior helper struct we no longer need to mess
> around with void* pointers in order to propagate anon_vma_name, and this
> means we can get rid of the confusing and inconsistent visitor pattern
> implementation in madvise_vma_anon_name().
> 
> This means we now have a single state object that threads through most of
> madvise()'s logic and a single code path which executes the majority of
> madvise() behaviour (we maintain separate logic for failure injection and
> memory population for the time being).
> 
> We are able to remove the visitor pattern by handling the anon_vma_name
> setting logic via an internal madvise flag - __MADV_SET_ANON_VMA_NAME. This
> uses a negative value so it isn't reasonable that we will ever add this as
> a UAPI flag.
> 
> Additionally, the madvise_behavior_valid() check ensures that
> user-specified behaviours are strictly only those we permit which, of
> course, this flag will be excluded from.
> 
> We are able to propagate the anon_vma_name object through use of the
> madvise_behavior helper struct.
> 
> Doing this results in a can_modify_vma_madv() check for anonymous VMA name
> changes, however this will cause no issues as this operation is not
> prohibited.
> 
> We can also then reuse more code and drop the redundant
> madvise_vma_anon_name() function altogether.
> 
> Additionally separate out behaviours that update VMAs from those that do
> not.

Nice work!

> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

Reviewed-by: SeongJae Park <sj@...nel.org>


Thanks,
SJ

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