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From:   Miles Chen <miles.chen@mediatek.com>
To:     <robin.murphy@arm.com>
CC:     <iommu@lists.linux-foundation.org>, <joro@8bytes.org>,
        <linux-kernel@vger.kernel.org>, <miles.chen@mediatek.com>,
        <stable@vger.kernel.org>, <will@kernel.org>,
        <wsd_upstream@mediatek.com>, <yf.wang@mediatek.com>
Subject: Re: [PATCH] iommu/iova: Improve 32-bit free space estimate
Date:   Sat, 5 Mar 2022 08:03:37 +0800
Message-ID: <20220305000337.24995-1-miles.chen@mediatek.com>
In-Reply-To: <77b0c978-7caa-c333-6015-1d784b5daf3f@arm.com>
References: <77b0c978-7caa-c333-6015-1d784b5daf3f@arm.com>
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Hi Joerg, Robin,

> Applied without stable tag for now. If needed, please consider
> re-sending it for stable when this patch is merged upstream.

> Yeah, having figured out the history, I ended up with the opinion that 
> it was a missed corner-case optimisation opportunity, rather than an 
> actual error with respect to intent or implementation, so I 
> intentionally left that out. Plus figuring out an exact Fixes tag might 
> be tricky - as above I reckon it probably only started to become 
> significant somwehere around 5.11 or so.
> 
> All of these various levels of retry mechanisms are only a best-effort 
> thing, and ultimately if you're making large allocations from a small 
> space there are always going to be *some* circumstances that still 
> manage to defeat them. Over time, we've made them try harder, but that 
> fact that we haven't yet made them try hard enough to work well for a 
> particular use-case does not constitute a bug. However as Joerg says, 
> anyone's welcome to make a case to Greg to backport a mainline commit if 
> it's a low-risk change with significant benefit to real-world stable 
> kernel users.

Got it, thank you. 
We will try to push to the android LTS trees we need.

Thanks,
Miles

> 
> Thanks all!
> 
> Robin.