linux-kernel - Re: [PATCH 05/44] kdbus: Add comment on merging free pool slices

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Message-ID: <CANq1E4R7830444KFbQQ3DZXcNWYpmVm-708Q7jbj82KmC=jXcQ@mail.gmail.com>
Date:	Thu, 8 Oct 2015 15:50:46 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	Sergei Zviagintsev <sergei@...v.net>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Daniel Mack <daniel@...que.org>,
	David Herrmann <dh.herrmann@...glemail.com>,
	Djalal Harouni <tixxdz@...ndz.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 05/44] kdbus: Add comment on merging free pool slices

Hi

On Thu, Oct 8, 2015 at 1:31 PM, Sergei Zviagintsev <sergei@...v.net> wrote:
> Add comment on why we remove the same slice from free slices tree and
> then add it back again when merging the slice to be released with
> previous free slice.
>
> Signed-off-by: Sergei Zviagintsev <sergei@...v.net>
> ---
>  ipc/kdbus/pool.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/ipc/kdbus/pool.c b/ipc/kdbus/pool.c
> index 84afe96fbc22..c26ef963d8d1 100644
> --- a/ipc/kdbus/pool.c
> +++ b/ipc/kdbus/pool.c
> @@ -304,6 +304,12 @@ static void __kdbus_pool_slice_release(struct kdbus_pool_slice *slice)
>                 s = list_entry(slice->entry.prev,
>                                struct kdbus_pool_slice, entry);
>                 if (s->free) {
> +                       /*
> +                        * As size of slice increases after merge and free
> +                        * slices tree is ordered by slice size, we have to
> +                        * remove the slice from free slices tree and then add
> +                        * it again to keep the tree balanced.
> +                        */

Mhh, isn't this obvious? "slices_free" is ordered by s->size, so a
change of the key requires a re-insert. If you disagree, maybe keep it
simple:

        /* s->size changed, re-insert slice in rbtree */

Thanks
David

>                         rb_erase(&s->rb_node, &pool->slices_free);
>                         list_del(&slice->entry);
>                         s->size += slice->size;
> --
> 1.8.3.1
>
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