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Date: Fri, 2 Feb 2024 04:05:03 +0000
From: Al Viro <viro@zeniv.linux.org.uk>
To: Doug Anderson <dianders@chromium.org>
Cc: Christian Brauner <brauner@kernel.org>,
	Eric Biederman <ebiederm@xmission.com>, Jan Kara <jack@suse.cz>,
	Kees Cook <keescook@chromium.org>, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] regset: use vmalloc() for regset_get_alloc()
Message-ID: <20240202040503.GX2087318@ZenIV>
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Sender: Al Viro <viro@ftp.linux.org.uk>

On Fri, Feb 02, 2024 at 03:49:25AM +0000, Al Viro wrote:
> On Thu, Feb 01, 2024 at 07:15:48PM -0800, Doug Anderson wrote:
> > >
> > > Well, the next step would be to see which regset it is - if you
> > > see that kind of allocation, print regset->n, regset->size and
> > > regset->core_note_type.
> > 
> > Of course! Here are the big ones:
> > 
> > [   45.875574] DOUG: Allocating 279584 bytes, n=17474, size=16,
> > core_note_type=1029
> 
> 0x405, NT_ARM_SVE
>         [REGSET_SVE] = { /* Scalable Vector Extension */
>                 .core_note_type = NT_ARM_SVE,
>                 .n = DIV_ROUND_UP(SVE_PT_SIZE(SVE_VQ_MAX, SVE_PT_REGS_SVE),
>                                   SVE_VQ_BYTES),
>                 .size = SVE_VQ_BYTES,
> 
> IDGI.  Wasn't SVE up to 32 * 2Kbit, i.e. 8Kbyte max?  Any ARM folks around?
> Sure, I understand that it's variable-sized and we want to allocate enough
> for the worst case, but can we really get about 280Kb there?  Context switches
> would be really unpleasant on such boxen...

FWIW, this apparently intends to be "variable, up to SVE_PT_SIZE(...) bytes";
no idea if SVE_PT_SIZE is the right thing to use here.