On Fri, Jun 15, 2018 at 12:43:10PM +0800, Wei Wang wrote: > +/** > + * get_from_free_page_list - get free page blocks from a free page list > + * @order: the order of the free page list to check > + * @buf: the array to store the physical addresses of the free page blocks > + * @size: the array size > + * > + * This function offers hints about free pages. There is no guarantee that > + * the obtained free pages are still on the free page list after the function > + * returns. pfn_to_page on the obtained free pages is strongly discouraged > + * and if there is an absolute need for that, make sure to contact MM people > + * to discuss potential problems. > + * > + * The addresses are currently stored to the array in little endian. This > + * avoids the overhead of converting endianness by the caller who needs data > + * in the little endian format. Big endian support can be added on demand in > + * the future. > + * > + * Return the number of free page blocks obtained from the free page list. > + * The maximum number of free page blocks that can be obtained is limited to > + * the caller's array size. > + */
Please use: * Return: The number of free page blocks obtained from the free page list. Also, please include a * Context: Any context. or * Context: Process context. or whatever other conetext this function can be called from. Since you're taking the lock irqsafe, I assume this can be called from any context, but I wonder if it makes sense to have this function callable from interrupt context. Maybe this should be callable from process context only. > +uint32_t get_from_free_page_list(int order, __le64 buf[], uint32_t size) > +{ > + struct zone *zone; > + enum migratetype mt; > + struct page *page; > + struct list_head *list; > + unsigned long addr, flags; > + uint32_t index = 0; > + > + for_each_populated_zone(zone) { > + spin_lock_irqsave(&zone->lock, flags); > + for (mt = 0; mt < MIGRATE_TYPES; mt++) { > + list = &zone->free_area[order].free_list[mt]; > + list_for_each_entry(page, list, lru) { > + addr = page_to_pfn(page) << PAGE_SHIFT; > + if (likely(index < size)) { > + buf[index++] = cpu_to_le64(addr); > + } else { > + spin_unlock_irqrestore(&zone->lock, > + flags); > + return index; > + } > + } > + } > + spin_unlock_irqrestore(&zone->lock, flags); > + } > + > + return index; > +} I wonder if (to address Michael's concern), you shouldn't instead use the first free chunk of pages to return the addresses of all the pages. ie something like this: __le64 *ret = NULL; unsigned int max = (PAGE_SIZE << order) / sizeof(__le64); for_each_populated_zone(zone) { spin_lock_irq(&zone->lock); for (mt = 0; mt < MIGRATE_TYPES; mt++) { list = &zone->free_area[order].free_list[mt]; list_for_each_entry_safe(page, list, lru, ...) { if (index == size) break; addr = page_to_pfn(page) << PAGE_SHIFT; if (!ret) { list_del(...); ret = addr; } ret[index++] = cpu_to_le64(addr); } } spin_unlock_irq(&zone->lock); } return ret; } You'll need to return the page to the freelist afterwards, but free_pages() should take care of that. _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization