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keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-purgate-ID: tlsNG-4011c0/1787664512-51EC2CFC-112D4314/0/0 X-purgate-type: clean X-purgate-size: 2899 On 25.08.2026 13:42, George Dunlap wrote: > On Mon, Aug 24, 2026 at 10:02 AM Jan Beulich wrote: >> While these percentiles in particular of course look very tiny, they are >> applicable only on systems having no meaningful gaps in the physical >> address map. And even more generally I find all of these calculations >> only partly convincing, not the least because you start out from numbers >> which look pretty contrived when comparing to actual systems which would >> run the new code. (Using more realistic real-system values may end up >> going in favor of what you want to convey, or it may not.) > > To be honest, I'm inclined to think that they're not very convincing > because you don't actually have an idea what the problem is. You > didn't specify what you were worried about, so I tried to guess a > scenario that I considered 95th-percentile worse case. I don't know > what kinds of sparse memory layout machines you have in mind -- are > they written down anywhere, so that contributors can read and > understand what they need to consider *before* implementing? Even now > you haven't even said what about my scenario you consider unrealistic, > much less told me parameters you think are more realistic. What I specifically considered unrealistic is that you use huge pCPU and vCPU counts. Yes, you're trying to do a worst case estimate, yet at the same time you're assuming huge amounts of memory to be available (which doesn't represent a "worst case"). As to sparse layouts - ones which have led to the two forms of PDX compression are well known (I think). The need for more recent (offset) form is a good example of what could go wrong here: New machines can always come with new layouts, potentially requiring new compressions approaches. So what I'm concerned about is effectively _any_ sparse layout that we may encounter without having a suitable PDX compression method readily available. > I don't even know exactly what failure mode you're worried about. Two > kinds of potential failures I know about: > - Performance impacted because pages can't be NUMA-local > - Toolstack operations (including domain creation) fail because > xenheap has been exhausted. One thing I can't help thinking you keep overlooking throughout your reply: xenheap and domheap aren't separate. There being only a relatively small part of it needed for the worst case estimate you did means nothing as to exhausting the xenheap in practice: Almost the entirety of it (with the DMA reserve being somewhat protected) can be used to build domains. Once in that state, allocations would fail no matter that large swathes of domheap might (have become) available (again). That said, with what you indicated at the very bottom of your reply, it looks like this part of the discussion has become largely moot. Jan