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From:   Eric Dumazet <edumazet@google.com>
Date:   Fri, 31 Jan 2020 06:42:28 -0800
Message-ID: <CANn89iKfA+yPHiL4R7-jkewwhDgM6jkwhW5o9H=VL9CnyBikhw@mail.gmail.com>
Subject: Re: [PATCH] dma-debug: dynamic allocation of hash table
To:     Robin Murphy <robin.murphy@arm.com>
Cc:     Christoph Hellwig <hch@lst.de>, Joerg Roedel <jroedel@suse.de>,
        iommu@lists.linux-foundation.org,
        Eric Dumazet <eric.dumazet@gmail.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
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On Fri, Jan 31, 2020 at 4:30 AM Robin Murphy <robin.murphy@arm.com> wrote:
>
> ...and when that represents ~5% of the total system RAM it is a *lot*
> less reasonable than even 12KB. As I said, it's great to make a debug
> option more efficient such that what it observes is more representative
> of the non-debug behaviour, but it mustn't come at the cost of making
> the entire option unworkable for other users.
>

Then I suggest you send a patch to reduce PREALLOC_DMA_DEBUG_ENTRIES
because having 65536 preallocated entries consume 4 MB of memory.

Actually this whole attempt to re-implement slab allocations in this
file is suspect.

Do not get me wrong, but if you really want to run linux on a 16MB host,
I guess you need to add CONFIG_BASE_SMALL all over the places,
not only in this kernel/dma/debug.c file.