linux-kernel - Re: [PATCH v3 1/1] swiotlb: Track and report io_tlb

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Message-ID: <20230407055016.GA6803@lst.de>
Date:   Fri, 7 Apr 2023 07:50:16 +0200
From:   Christoph Hellwig <hch@....de>
To:     Michael Kelley <mikelley@...rosoft.com>
Cc:     hch@....de, m.szyprowski@...sung.com, robin.murphy@....com,
        decui@...rosoft.com, tiala@...rosoft.com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] swiotlb: Track and report io_tlb_used high
 water mark in debugfs

On Fri, Mar 31, 2023 at 09:45:00PM -0700, Michael Kelley wrote:
> Changes in v3:
> * Do high water mark accounting only when CONFIG_DEBUG_FS=y. As
>   as a result, add back the mem_used() function for the "swiotlb
>   buffer is full" error message. [Christoph -- I didn't hear back
>   whether this approach addresses your concern about one additional
>   atomic operation when slots are allocated and again when freed. I've
>   gone ahead with this new version, and we can obviously have further
>   discussion.]

Still not too happy, but at least debugfs is an interfact we could
remove at any time.

But can you please factor the used_hiwater accounting into two
separate helpers that are udner CONFIG_DEBUG_FS and otherwise
stubbed out, instead of adding the logic directly into
swiotlb_do_find_slots and swiotlb_release_slots?