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Date: Wed, 22 May 2024 18:05:31 +0100
From: Catalin Marinas <catalin.marinas@arm.com>
To: Steven Price <steven.price@arm.com>
Cc: kvm@vger.kernel.org, kvmarm@lists.linux.dev,
	Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>,
	James Morse <james.morse@arm.com>,
	Oliver Upton <oliver.upton@linux.dev>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
	Joey Gouly <joey.gouly@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Christoffer Dall <christoffer.dall@arm.com>,
	Fuad Tabba <tabba@google.com>, linux-coco@lists.linux.dev,
	Ganapatrao Kulkarni <gankulkarni@os.amperecomputing.com>
Subject: Re: [PATCH v2 12/14] arm64: realm: Support nonsecure ITS emulation
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 <20240412084213.1733764-13-steven.price@arm.com>
 <ZkSV7Z8QFQYLETzD@arm.com>
 <74011ac1-34e0-4ee3-a00d-f78ad334fce2@arm.com>
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In-Reply-To: <74011ac1-34e0-4ee3-a00d-f78ad334fce2@arm.com>

On Wed, May 22, 2024 at 04:52:45PM +0100, Steven Price wrote:
> On 15/05/2024 12:01, Catalin Marinas wrote:
> > On Fri, Apr 12, 2024 at 09:42:11AM +0100, Steven Price wrote:
> >> @@ -3432,7 +3468,16 @@ static struct its_device *its_create_device(struct its_node *its, u32 dev_id,
> >>  	nr_ites = max(2, nvecs);
> >>  	sz = nr_ites * (FIELD_GET(GITS_TYPER_ITT_ENTRY_SIZE, its->typer) + 1);
> >>  	sz = max(sz, ITS_ITT_ALIGN) + ITS_ITT_ALIGN - 1;
> >> -	itt = kzalloc_node(sz, GFP_KERNEL, its->numa_node);
> >> +	itt_order = get_order(sz);
> >> +	page = its_alloc_shared_pages_node(its->numa_node,
> >> +					   GFP_KERNEL | __GFP_ZERO,
> >> +					   itt_order);
> > 
> > How much do we waste by going for a full page always if this is going to
> > be used on the host?
> 
> sz is a minimum of ITS_ITT_ALIGN*2-1 - which is 511 bytes. So
> potentially PAGE_SIZE-512 bytes could be wasted here (minus kmalloc
> overhead).

That I figured out as well but how many times is this path called with a
size smaller than a page?

-- 
Catalin