linux-kernel - Re: [PATCH RFC v1 2/6] swiotlb: convert variables to arrays

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Date:   Thu, 4 Feb 2021 11:49:23 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>,
        Dongli Zhang <dongli.zhang@...cle.com>
Cc:     dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        iommu@...ts.linux-foundation.org, linux-mips@...r.kernel.org,
        linux-mmc@...r.kernel.org, linux-pci@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, nouveau@...ts.freedesktop.org,
        x86@...nel.org, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org, adrian.hunter@...el.com,
        akpm@...ux-foundation.org, benh@...nel.crashing.org,
        bskeggs@...hat.com, bhelgaas@...gle.com, bp@...en8.de,
        boris.ostrovsky@...cle.com, chris@...is-wilson.co.uk,
        daniel@...ll.ch, airlied@...ux.ie, hpa@...or.com, mingo@...nel.org,
        mingo@...hat.com, jani.nikula@...ux.intel.com,
        joonas.lahtinen@...ux.intel.com, jgross@...e.com,
        konrad.wilk@...cle.com, m.szyprowski@...sung.com,
        matthew.auld@...el.com, mpe@...erman.id.au, rppt@...nel.org,
        paulus@...ba.org, peterz@...radead.org, rodrigo.vivi@...el.com,
        sstabellini@...nel.org, bauerman@...ux.ibm.com,
        tsbogend@...ha.franken.de, tglx@...utronix.de,
        ulf.hansson@...aro.org, joe.jin@...cle.com,
        thomas.lendacky@....com, Claire Chang <tientzu@...omium.org>
Subject: Re: [PATCH RFC v1 2/6] swiotlb: convert variables to arrays

On 2021-02-04 07:29, Christoph Hellwig wrote:
> On Wed, Feb 03, 2021 at 03:37:05PM -0800, Dongli Zhang wrote:
>> This patch converts several swiotlb related variables to arrays, in
>> order to maintain stat/status for different swiotlb buffers. Here are
>> variables involved:
>>
>> - io_tlb_start and io_tlb_end
>> - io_tlb_nslabs and io_tlb_used
>> - io_tlb_list
>> - io_tlb_index
>> - max_segment
>> - io_tlb_orig_addr
>> - no_iotlb_memory
>>
>> There is no functional change and this is to prepare to enable 64-bit
>> swiotlb.
> 
> Claire Chang (on Cc) already posted a patch like this a month ago,
> which looks much better because it actually uses a struct instead
> of all the random variables.

Indeed, I skimmed the cover letter and immediately thought that this 
whole thing is just the restricted DMA pool concept[1] again, only from 
a slightly different angle.

Robin.

[1] 
https://lore.kernel.org/linux-iommu/20210106034124.30560-1-tientzu@chromium.org/