Ok.....thanks for the sharing....what u said makes sense....:-). Ok....i must keep repeating to myself: unusing the pgdat.....for the physical node removed........wow... "unused" and "removal" really makes a great semantic differences here... On Sat, Aug 2, 2008 at 2:13 AM, Johannes Weiner <hannes@xxxxxxxxxxxx> wrote: > Hi Peter, > > Peter Teoh <htmldeveloper@xxxxxxxxx> writes: > >> http://www.gossamer-threads.com/lists/linux/kernel/954421?page=last >> >> Someone please help me out: >> >> a. What is pgdat? From header - I read but cannot find the >> motivation behind all these: >> >> /* >> * The pg_data_t structure is used in machines with CONFIG_DISCONTIGMEM >> * (mostly NUMA machines?) to denote a higher-level memory zone than the >> * zone denotes. >> * >> * On NUMA machines, each NUMA node would have a pg_data_t to describe >> * it's memory layout. >> * >> * Memory statistics and page replacement data structures are >> maintained on a >> * per-zone basis. >> */ >> struct bootmem_data; >> typedef struct pglist_data { >> struct zone node_zones[MAX_NR_ZONES]; >> struct zonelist node_zonelists[MAX_ZONELISTS]; >> int nr_zones; >> #ifdef CONFIG_FLAT_NODE_MEM_MAP >> struct page *node_mem_map; >> #endif >> struct bootmem_data *bdata; >> #ifdef CONFIG_MEMORY_HOTPLUG >> /* >> * Must be held any time you expect node_start_pfn, >> node_present_pages >> * or node_spanned_pages stay constant. Holding this will also >> * guarantee that any pfn_valid() stays that way. >> * >> * Nests above zone->lock and zone->size_seqlock. >> */ >> spinlock_t node_size_lock; >> #endif >> unsigned long node_start_pfn; >> unsigned long node_present_pages; /* total number of physical >> pages */ >> unsigned long node_spanned_pages; /* total size of physical page >> range, including holes */ >> int node_id; >> wait_queue_head_t kswapd_wait; >> struct task_struct *kswapd; >> int kswapd_max_order; >> } pg_data_t; >> >> And why not u have to remove it? For what purposes? Why memory >> hotplug needs this feature off? >> >> And as today I can still can see the structure, so is the patch >> reversed? If so, then the memory hotplug must have got a >> replacement/substitution for this removal of pgdat - is that correct? > > It's not about removal of this structure but a removal of physical nodes > when you hot-unplug the memory. The kernel has to cope with that (unuse > the page frames of the node about to be removed). > > Hannes > -- Regards, Peter Teoh -- Regards, Peter Teoh -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
