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Mon, 19 Jan 2026 08:13:24 -0800 (PST) Message-ID: <858d73b3-2feb-419f-bf3b-9a264e9f9af8@suse.com> Date: Mon, 19 Jan 2026 17:13:25 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/3] xen/mm: limit non-scrubbed allocations to a specific order To: Roger Pau Monne Cc: Andrew Cooper , Anthony PERARD , Michal Orzel , Julien Grall , Stefano Stabellini , xen-devel@lists.xenproject.org References: <20260115111804.40199-1-roger.pau@citrix.com> <20260115111804.40199-4-roger.pau@citrix.com> Content-Language: en-US From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; 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: <20260115111804.40199-4-roger.pau@citrix.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 15.01.2026 12:18, Roger Pau Monne wrote: > The current logic allows for up to 1G pages to be scrubbed in place, which > can cause the watchdog to trigger in practice. Reduce the limit for > in-place scrubbed allocations to a newly introduced define: > CONFIG_DIRTY_MAX_ORDER. This currently defaults to CONFIG_DOMU_MAX_ORDER > on all architectures. Also introduce a command line option to set the > value. > > Fixes: 74d2e11ccfd2 ("mm: Scrub pages in alloc_heap_pages() if needed") > Signed-off-by: Roger Pau Monné > --- > Changes since v1: > - Split from previous patch. > - Introduce a command line option to set the limit. > --- > docs/misc/xen-command-line.pandoc | 9 +++++++++ > xen/common/page_alloc.c | 23 ++++++++++++++++++++++- > 2 files changed, 31 insertions(+), 1 deletion(-) If you confine the change to page_alloc.c, won't this mean that patch 2's passing of MEMF_no_scrub will then also be bounded (in which case the need for patch 2 would largely disappear)? > --- a/docs/misc/xen-command-line.pandoc > +++ b/docs/misc/xen-command-line.pandoc > @@ -1822,6 +1822,15 @@ Specify the deepest C-state CPUs are permitted to be placed in, and > optionally the maximum sub C-state to be used used. The latter only applies > to the highest permitted C-state. > > +### max-order-dirty > +> `= ` > + > +Specify the maximum allocation order allowed when scrubbing allocated pages > +in-place. The allocation is non-preemptive, and hence the value must be keep > +low enough to avoid hogging the CPU for too long. > + > +Defaults to `CONFIG_DIRTY_MAX_ORDER` or if unset to `CONFIG_DOMU_MAX_ORDER`. This may end up misleading, as - despite their names - these aren't really Kconfig settings that people could easily control in their builds. > ### max_gsi_irqs (x86) > > `= ` I also wonder whether your addition wouldn't more naturally go a litter further down, by assuming / implying that the sorting used largely ignores separator characters (underscore vs dash here). Jan