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Wed, 04 Mar 2026 08:31:26 -0800 (PST) Message-ID: <5e4d4674-1e1a-4902-bcd0-a24fbd13dc8e@suse.com> Date: Wed, 4 Mar 2026 17:31:24 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 02/10] xen/page_alloc: Optimize getting per-NUMA-node free page counts To: Bernhard Kaindl Cc: Andrew Cooper , Anthony PERARD , Michal Orzel , Julien Grall , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , Stefano Stabellini , xen-devel@lists.xenproject.org References: 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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 26.02.2026 15:29, Bernhard Kaindl wrote: > From: Alejandro Vallejo > > Add per-node free page counters (node_avail_pages[]), protected by > heap_lock, updated in real-time in lockstep with total_avail_pages > as pages are allocated and freed. > > This replaces the avail_heap_pages() loop over all online nodes and > zones in avail_node_heap_pages() with a direct O(1) array lookup, > making it efficient to get the total free pages for a given NUMA node. > > The per-node counts are currently provided using sysctl for NUMA > placement decisions of domain builders and monitoring, and for > debugging with the debug-key 'u' to print NUMA info to the printk buffer. > > They will also be used for checking if a NUMA node may be able to > satisfy a NUMA-node-specific allocation by comparing node availability > against node-specific claims before looking for pages in the zones > of the node. > > Also change total_avail_pages and outstanding_claims to unsigned long: > > Those never become negative (we protect that with ASSERT/BUG_ON already), > and converting them to unsigned long makes that explicit, and also > fixes signed/unsigned comparison warnings. This wants to be a separate commit. It hasn't got anything to do in here. > This only needs moving the ASSERT to before the subtraction. > See the previous commit moving the BUG_ON for outstanding_claims. Please can you avoid such statements? You won't know in which order the patches are committed: Patch 01 may go in weeks or months before patch 02. > --- a/xen/common/page_alloc.c > +++ b/xen/common/page_alloc.c > @@ -483,11 +483,32 @@ static heap_by_zone_and_order_t *_heap[MAX_NUMNODES]; > > static unsigned long node_need_scrub[MAX_NUMNODES]; > > +/* avail[node][zone] is the number of free pages on that node and zone. */ > static unsigned long *avail[MAX_NUMNODES]; > -static long total_avail_pages; > +/* Global available pages, updated in real-time, protected by heap_lock */ > +static unsigned long total_avail_pages; > > +/* The global heap lock, protecting access to the heap and related structures */ > static DEFINE_SPINLOCK(heap_lock); > -static long outstanding_claims; /* total outstanding claims by all domains */ > + > +/* > + * Per-node count of available pages, protected by heap_lock, updated in > + * lockstep with total_avail_pages as pages are allocated and freed. > + * > + * Each entry holds the sum of avail[node][zone] across all zones, used for > + * efficiently checking node-local availability for allocation requests. > + * Also provided via sysctl for NUMA placement decisions of domain builders > + * and monitoring, and logged with debug-key 'u' for NUMA debugging. > + * > + * Maintaining this under heap_lock does not reduce scalability, as the > + * allocator is already serialized on it. The accessor macro abstracts the > + * storage to ease future changes (e.g. moving to per-node lock granularity). > + */ > +#define node_avail_pages(node) (node_avail_pages[node]) This isn't really needed when ... > +static unsigned long node_avail_pages[MAX_NUMNODES]; ... it's a static array anyway. Plus you may want to talk to Andrew regarding the use of such a macro as an lvalue. > +/* total outstanding claims by all domains */ > +static unsigned long outstanding_claims; As you touch it, comment style wants correcting. Jan