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From: Marc Orr <marcorr@google.com>
Date: Wed, 31 Oct 2018 14:24:24 -0700
Message-ID: <CAA03e5F7LsYcrr6fgHWdwQ=hyYm2Su7Lqke7==Un7tSp57JtSA@mail.gmail.com>
Subject: Re: [kvm PATCH v5 2/4] kvm: x86: Dynamically allocate guest_fpu
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To: dave.hansen@intel.com
Cc: kvm@vger.kernel.org, Jim Mattson <jmattson@google.com>, David Rientjes <rientjes@google.com>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, linux-mm@kvack.org, akpm@linux-foundation.org, pbonzini@redhat.com, rkrcmar@redhat.com, willy@infradead.org, sean.j.christopherson@intel.com, dave.hansen@linux.intel.com, Wanpeng Li <kernellwp@gmail.com>

> It can get set to sizeof(struct fregs_state) for systems where XSAVE is
> not in use.  I was neglecting to mention those when I said the "~500
> byte" number.
>
> My point was that it can vary wildly and that any static allocation
> scheme will waste lots of memory when we have small hardware-supported
> buffers.

Got it. Then I think we need to set the size for the kmem cache to
max(fpu_kernel_xstate_size, sizeof(fxregs_state)), unless I'm missing
something. I'll send out a version of the patch that does this in a
bit. Thanks!