Re: [PATCH v2 1/5] mm/madvise: remove the visitor pattern and thread anon_vma state

[SeongJae Park <sj@kernel.org>]

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

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


Thanks,
SJ

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