linux-kernel - Re: [PATCH] net: thunderx: rework mac addresses list to u64 array

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Message-ID: <20180405160749.GB12703@localhost.localdomain>
Date:   Thu, 5 Apr 2018 09:07:49 -0700
From:   Vadim Lomovtsev <Vadim.Lomovtsev@...iumnetworks.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     sgoutham@...ium.com, sunil.kovvuri@...il.com, rric@...nel.org,
        linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, davem@...emloft.net,
        dnelson@...hat.com, gustavo@...eddedor.com,
        Vadim Lomovtsev <Vadim.Lomovtsev@...ium.com>
Subject: Re: [PATCH] net: thunderx: rework mac addresses list to u64 array

Hi Christoph,

Thank you for your feedback and time.

On Thu, Apr 05, 2018 at 08:07:48AM -0700, Christoph Hellwig wrote:
> >  struct xcast_addr_list {
> > -	struct list_head list;
> >  	int              count;
> > +	u64              mc[0];
> 
> Please use the standard C99 syntax here:
> 
> 	u64              mc[];

Ok, will update.

> 
> > +				mc_list = kmalloc(sizeof(*mc_list) +
> > +						  sizeof(u64) * netdev_mc_count(netdev),
> > +						  GFP_ATOMIC);
> 
> kmalloc_array(), please.

In this case it would require two memory allocation calls to kmalloc() for
xcast_addr_list struct and to kmalloc_array() for 'mc' addresses, becasue of
different data types and so two null-ptr checks .. this is what I'd like get rid off.

My idea of this was to keep number of array elements and themselves within the
same memory block/page to reduce number of memory allocation requests, number
of allocated pages/blocks and avoid possible memory fragmentation (however, I believe
the latter is already handled at the mm layer).

WBR,
Vadim