linux-kernel - Re: [PATCH v5 1/7] list: Add function list_rotate_to

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Date:   Wed, 3 Apr 2019 17:57:42 +0000
From:   Roman Gushchin <guro@...com>
To:     "Tobin C. Harding" <tobin@...nel.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Matthew Wilcox <willy@...radead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 1/7] list: Add function list_rotate_to_front()

On Wed, Apr 03, 2019 at 10:05:39AM +1100, Tobin C. Harding wrote:
> Currently if we wish to rotate a list until a specific item is at the
> front of the list we can call list_move_tail(head, list).  Note that the
> arguments are the reverse way to the usual use of list_move_tail(list,
> head).  This is a hack, it depends on the developer knowing how the
> list_head operates internally which violates the layer of abstraction
> offered by the list_head.  Also, it is not intuitive so the next
> developer to come along must study list.h in order to fully understand
> what is meant by the call, while this is 'good for' the developer it
> makes reading the code harder.  We should have an function appropriately
> named that does this if there are users for it intree.
> 
> By grep'ing the tree for list_move_tail() and list_tail() and attempting
> to guess the argument order from the names it seems there is only one
> place currently in the tree that does this - the slob allocatator.
> 
> Add function list_rotate_to_front() to rotate a list until the specified
> item is at the front of the list.
> 
> Signed-off-by: Tobin C. Harding <tobin@...nel.org>

Reviewed-by: Roman Gushchin <guro@...com>