linux-kernel - Re: __GFP_REPEAT usage in fq_alloc

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Message-ID: <CANn89iLy2KMUu80KekhvO31G4uXr4B0K8zvGjhfyBBp9d_ncBg@mail.gmail.com>
Date:   Fri, 6 Jan 2017 08:48:49 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: __GFP_REPEAT usage in fq_alloc_node

On Fri, Jan 6, 2017 at 8:31 AM, Vlastimil Babka <vbabka@...e.cz> wrote:

>
> I wonder what's that cause of the penalty (when accessing the vmapped
> area I suppose?) Is it higher risk of collisions cache misses within the
> area, compared to consecutive physical adresses?

I believe tests were done with 48 fq qdisc, each having 2^16 slots.
So I had 48 blocs,of 524288 bytes.

Trying a bit harder at setup time to get 128 consecutive pages got
less TLB pressure.