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Message-ID: <2023042617-wobble-enlighten-9361@gregkh>
Date: Wed, 26 Apr 2023 14:26:36 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Petr Tesařík <petr@...arici.cz>
Cc: Petr Tesarik <petrtesarik@...weicloud.com>,
Jonathan Corbet <corbet@....net>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>,
Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...il.com>,
Daniel Vetter <daniel@...ll.ch>,
Christoph Hellwig <hch@....de>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Robin Murphy <robin.murphy@....com>,
Borislav Petkov <bp@...e.de>,
"Paul E. McKenney" <paulmck@...nel.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Zhen Lei <thunder.leizhen@...wei.com>,
Randy Dunlap <rdunlap@...radead.org>,
Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
Kim Phillips <kim.phillips@....com>,
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Muchun Song <muchun.song@...ux.dev>,
Ondrej Zary <linux@...y.sk>,
"Jason A. Donenfeld" <Jason@...c4.com>,
Petr Tesarik <petr.tesarik.ext@...wei.com>,
Hans de Goede <hdegoede@...hat.com>,
Dan Williams <dan.j.williams@...el.com>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Kees Cook <keescook@...omium.org>,
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Roberto Sassu <roberto.sassu@...wei.com>,
Kefeng Wang <wangkefeng.wang@...wei.com>
Subject: Re: [PATCH v2 0/7] Allow dynamic allocation of software IO TLB
bounce buffers
On Wed, Apr 26, 2023 at 02:15:20PM +0200, Petr Tesařík wrote:
> Hi,
>
> On Wed, 19 Apr 2023 12:03:52 +0200
> Petr Tesarik <petrtesarik@...weicloud.com> wrote:
>
> > From: Petr Tesarik <petr.tesarik.ext@...wei.com>
> >
> > The goal of my work is to provide more flexibility in the sizing of
> > SWIOTLB.
> >
> > The software IO TLB was designed with these assumptions:
> >
> > 1. It would not be used much, especially on 64-bit systems.
> > 2. A small fixed memory area (64 MiB by default) is sufficient to
> > handle the few cases which require a bounce buffer.
> > 3. 64 MiB is little enough that it has no impact on the rest of the
> > system.
> >
> > First, if SEV is active, all DMA must be done through shared
> > unencrypted pages, and SWIOTLB is used to make this happen without
> > changing device drivers. The software IO TLB size is increased to
> > 6% of total memory in sev_setup_arch(), but that is more of an
> > approximation. The actual requirements may vary depending on the
> > amount of I/O and which drivers are used. These factors may not be
> > know at boot time, i.e. when SWIOTLB is allocated.
> >
> > Second, other colleagues have noticed that they can reliably get
> > rid of occasional OOM kills on an Arm embedded device by reducing
> > the SWIOTLB size. This can be achieved with a kernel parameter, but
> > determining the right value puts additional burden on pre-release
> > testing, which could be avoided if SWIOTLB is allocated small and
> > grows only when necessary.
>
> Now that merging into 6.4 has begun, what about this patch series? I'm
> eager to get some feedback (positive or negative) and respin the next
> version.
It's the merge window, we can't add new things that haven't been in
linux-next already. Please resubmit it after -rc1 is out.
thanks,
greg k-h
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