linux-kernel - Re: [PATCHv2 net 0/3] net: add support for flex_array_resize in flex

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Message-ID: <20181212120015.GA7637@hmswarspite.think-freely.org>
Date:   Wed, 12 Dec 2018 07:00:15 -0500
From:   Neil Horman <nhorman@...driver.com>
To:     David Miller <davem@...emloft.net>
Cc:     lucien.xin@...il.com, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-sctp@...r.kernel.org,
        marcelo.leitner@...il.com, dave.hansen@...ux.intel.com,
        rientjes@...gle.com, eparis@...hat.com, khorenko@...tuozzo.com
Subject: Re: [PATCHv2 net 0/3] net: add support for flex_array_resize in
 flex_array

On Tue, Dec 11, 2018 at 10:50:00PM -0800, David Miller wrote:
> From: Xin Long <lucien.xin@...il.com>
> Date: Fri,  7 Dec 2018 14:30:32 +0800
> 
> > Without the support for the total_nr_elements's growing or shrinking
> > dynamically, flex_array is not that 'flexible'. Like when users want
> > to change the size, they have to redo flex_array_alloc and copy all
> > the elements from the old to the new one.  The worse thing is every
> > element's memory gets changed.
> > 
> > To implement flex_array_resize based on current code, the difficult
> > thing is to process the size border of FLEX_ARRAY_BASE_BYTES_LEFT,
> > where the base data memory may change to an array for the 2nd level
> > data memory for growing, likewise for shrinking.
> > 
> > To make this part easier, we separate the base data memory and define
> > FLEX_ARRAY_BASE_SIZE as a same value of FLEX_ARRAY_PART_SIZE, as Neil
> > suggested.  When new size is crossing the border, the base memory is
> > allocated as the array for the 2nd level data memory and its part[0]
> > is pointed to the old base memory, and do the opposite for shrinking.
> > 
> > But it doesn't do any memory allocation or shrinking for elements in
> > flex_array_resize, as which should be done by flex_array_prealloc or
> > flex_array_shrink called by users.  No memory leaks can be caused by
> > that.
> > 
> > SCTP has benefited a lot from flex_array_resize() for managing its
> > stream memory so far.
> > 
> > v1->v2:
> >   Cc LKML and more developers.
> 
> So I don't know what to do about this series.
> 
> One of the responses stated that it has been proposed to remove flex_array
> and I don't know what to make of that, nor can I tell if that makes this
> series inappropriate or not.
> 


I suggest xin respond to messageid 20180523011821.12165-6-kent.overstreet@...il.com>
and send a NAK, indicating that his patch seems like it will break the build,
as, looking through it, it never removes flex_array calls from the sctp code.
If kent reposts with a conversion of the sctp code to radix trees, we're done.
If not, you can move forward with this commit.

Neil