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Date:   Wed, 11 Oct 2023 11:48:12 -0400
From:   "Liam R. Howlett" <Liam.Howlett@Oracle.com>
To:     Peng Zhang <zhangpeng.00@bytedance.com>
Cc:     maple-tree@lists.infradead.org, linux-mm@kvack.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, corbet@lwn.net,
        akpm@linux-foundation.org, willy@infradead.org, brauner@kernel.org,
        surenb@google.com, michael.christie@oracle.com, mjguzik@gmail.com,
        mathieu.desnoyers@efficios.com, npiggin@gmail.com,
        peterz@infradead.org, oliver.sang@intel.com, mst@redhat.com
Subject: Re: [PATCH v4 09/10] maple_tree: Preserve the tree attributes when
 destroying maple tree
Message-ID: <20231011154812.d26o6iqxflbmd2n3@revolver>
Mail-Followup-To: "Liam R. Howlett" <Liam.Howlett@Oracle.com>,
        Peng Zhang <zhangpeng.00@bytedance.com>,
        maple-tree@lists.infradead.org, linux-mm@kvack.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, corbet@lwn.net,
        akpm@linux-foundation.org, willy@infradead.org, brauner@kernel.org,
        surenb@google.com, michael.christie@oracle.com, mjguzik@gmail.com,
        mathieu.desnoyers@efficios.com, npiggin@gmail.com,
        peterz@infradead.org, oliver.sang@intel.com, mst@redhat.com
References: <20231009090320.64565-1-zhangpeng.00@bytedance.com>
 <20231009090320.64565-10-zhangpeng.00@bytedance.com>
 <1632d0e6-2d52-43b1-8a01-056231c0819d@bytedance.com>
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* Peng Zhang <zhangpeng.00@bytedance.com> [231011 11:42]:
>=20
>=20
> =E5=9C=A8 2023/10/9 17:03, Peng Zhang =E5=86=99=E9=81=93:
> > When destroying maple tree, preserve its attributes and then turn it
> > into an empty tree. This allows it to be reused without needing to be
> > reinitialized.
> >=20
> > Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
> > ---
> >   lib/maple_tree.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >=20
> > diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> > index d5544382ff15..1745242092fb 100644
> > --- a/lib/maple_tree.c
> > +++ b/lib/maple_tree.c
> > @@ -6775,7 +6775,7 @@ void __mt_destroy(struct maple_tree *mt)
> >   	if (xa_is_node(root))
> >   		mte_destroy_walk(root, mt);
> > -	mt->ma_flags =3D 0;
> > +	mt->ma_flags =3D mt_attr(mt)If I put everything into exit_mmap() for =
handling, this patch would
> not be necessary. But I think this patch is reasonable as it simply
> deletes all elements without requiring us to reinitialize the tree.
> What do you think?

Willy and I had debated if we should do what you have here a long time
ago.  There was an issue with the next exit_mmap() that would not have
arose with this change, which I was going to make before it was made
unnecessary due to other changes in the caller.

In the strict thinking of a destroy() call, I would expect the flags to
not be spared, but doing this allows for an easy way to clear out a tree
and resuse it as you have said.  I'm happy to keep this patch.


> >   }
> >   EXPORT_SYMBOL_GPL(__mt_destroy);