linux-kernel - Re: [PATCH] dma-debug: dynamic allocation of hash table

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Message-ID: <CAMuHMdVSyD62nvRmN-v6CbJ2UyqH=d7xdVeCD8_X5us+mvCXUQ@mail.gmail.com>
Date:   Fri, 31 Jan 2020 10:06:47 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Eric Dumazet <edumazet@...gle.com>, Christoph Hellwig <hch@....de>,
        Joerg Roedel <jroedel@...e.de>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dma-debug: dynamic allocation of hash table

Hi Robin,

On Fri, Jan 31, 2020 at 12:46 AM Robin Murphy <robin.murphy@....com> wrote:
> On 2020-01-30 7:10 pm, Eric Dumazet via iommu wrote:
> > Increasing the size of dma_entry_hash size by 327680 bytes
> > has reached some bootloaders limitations.
>
> [ That might warrant some further explanation - I don't quite follow how
> this would relate to a bootloader specifically :/ ]

Increasing the size of a static array increases kernel size.
Some (all? ;-) bootloaders have limitations on the maximum size of a
kernel image they can boot (usually something critical gets overwritten
when handling a too large image).  While boot loaders can be fixed and
upgraded, this is usually much more cumbersome than updating the
kernel.

Besides, a static array always consumes valuable unswapable memory,
even when the feature would not be used (e.g. disabled by a command
line option).

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds