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Date:   Mon, 3 Apr 2023 17:47:02 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     David Hildenbrand <david@redhat.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        Sean Christopherson <seanjc@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Joerg Roedel <jroedel@suse.de>,
        Ard Biesheuvel <ardb@kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Vlastimil Babka <vbabka@suse.cz>,
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        linux-mm@kvack.org, linux-coco@lists.linux.dev,
        linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCHv9 03/14] mm/page_alloc: Fake unaccepted memory
Message-ID: <20230403144702.uf7fhfrffypkmqy5@box.shutemov.name>
References: <20230330114956.20342-1-kirill.shutemov@linux.intel.com>
 <20230330114956.20342-4-kirill.shutemov@linux.intel.com>
 <053a9ccd-4205-7a76-70c3-c256bd995a1f@redhat.com>
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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@linux.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