linux-kernel - Re: [PATCHv9 03/14] mm/page_alloc: Fake unaccepted memory

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Date:   Mon, 3 Apr 2023 17:47:02 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     David Hildenbrand <david@...hat.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>,
        Ard Biesheuvel <ardb@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Dario Faggioli <dfaggioli@...e.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Mike Rapoport <rppt@...nel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        aarcange@...hat.com, peterx@...hat.com, x86@...nel.org,
        linux-mm@...ck.org, linux-coco@...ts.linux.dev,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv9 03/14] mm/page_alloc: Fake unaccepted memory

On Mon, Apr 03, 2023 at 04:43:08PM +0200, David Hildenbrand wrote:
> On 30.03.23 13:49, Kirill A. Shutemov wrote:
> > For testing purposes, it is useful to fake unaccepted memory in the
> > system. It helps to understand unaccepted memory overhead to the page
> > allocator.
> > 
> > The patch allows to treat memory above the specified physical memory
> > address as unaccepted.
> > 
> > The change only fakes unaccepted memory for page allocator. Memblock is
> > not affected.
> > 
> > It also assumes that arch-provided accept_memory() on already accepted
> > memory is a nop.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > ---
> >   mm/page_alloc.c | 21 +++++++++++++++++++++
> >   1 file changed, 21 insertions(+)
> > 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index d62fcb2f28bd..509a93b7e5af 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -7213,6 +7213,8 @@ static DEFINE_STATIC_KEY_FALSE(zones_with_unaccepted_pages);
> >   static bool lazy_accept = true;
> > +static unsigned long fake_unaccepted_start = -1UL;
> > +
> >   static int __init accept_memory_parse(char *p)
> >   {
> >   	if (!strcmp(p, "lazy")) {
> > @@ -7227,11 +7229,30 @@ static int __init accept_memory_parse(char *p)
> >   }
> >   early_param("accept_memory", accept_memory_parse);
> > +static int __init fake_unaccepted_start_parse(char *p)
> > +{
> > +	if (!p)
> > +		return -EINVAL;
> > +
> > +	fake_unaccepted_start = memparse(p, &p);
> > +
> > +	if (*p != '\0') {
> > +		fake_unaccepted_start = -1UL;
> > +		return -EINVAL;
> > +	}
> > +
> > +	return 0;
> > +}
> > +early_param("fake_unaccepted_start", fake_unaccepted_start_parse);
> > +
> >   static bool page_contains_unaccepted(struct page *page, unsigned int order)
> >   {
> >   	phys_addr_t start = page_to_phys(page);
> >   	phys_addr_t end = start + (PAGE_SIZE << order);
> > +	if (start >= fake_unaccepted_start)
> > +		return true;
> > +
> >   	return range_contains_unaccepted_memory(start, end);
> >   }
> 
> The "unpleasant" thing about this is, that page_contains_unaccepted() could
> not be used for sanity checks because the result is static.
> 
> For example, something like
> 
> if (page_contains_unaccepted(page, 0))
> 	accept_memory(page, 0);
> BUG_ON(!page_contains_unaccepted(page, 0));
> 
> Would work on real hardware, however, not for the fake variant.

Need for raw_page_contains_unaccepted()? :P

-- 
  Kiryl Shutsemau / Kirill A. Shutemov