David Hildenbrand <david@xxxxxxxxxx> writes:
> On 12.07.23 05:16, Aneesh Kumar K V wrote:
>> On 7/11/23 10:49 PM, David Hildenbrand wrote:
>>> On 11.07.23 06:48, Aneesh Kumar K.V wrote:
>>>> Add a new kconfig option that can be selected if we want to allow
>>>> pageblock alignment by reserving pages in the vmemmap altmap area.
>>>> This implies we will be reserving some pages for every memoryblock
>>>> This also allows the memmap on memory feature to be widely useful
>>>> with different memory block size values.
>>>
>>> "reserving pages" is a nice way of saying "wasting memory". :) Let's spell that out.
>>>
>>> I think we have to find a better name for this, and I think we should have a toggle similar to memory_hotplug.memmap_on_memory. This should be an admin decision, not some kernel config option.
>>>
>>>
>>> memory_hotplug.force_memmap_on_memory
>>>
>>> "Enable the memmap on memory feature even if it could result in memory waste due to memmap size limitations. For example, if the memmap for a memory block requires 1 MiB, but the pageblock size is 2 MiB, 1 MiB
>>> of hotplugged memory will be wasted. Note that there are still cases where the feature cannot be enforced: for example, if the memmap is smaller than a single page, or if the architecture does not support the forced mode in all configurations."
>>>
>>> Thoughts?
>>>
>>
>> With module parameter, do we still need the Kconfig option?
>
> No.
>
> Sleeping over this, maybe we can convert the existing
> memory_hotplug.memmap_on_memory parameter to also accept "force".
>
How about this?
modified mm/memory_hotplug.c
@@ -45,13 +45,67 @@
/*
* memory_hotplug.memmap_on_memory parameter
*/
-static bool memmap_on_memory __ro_after_init;
-module_param(memmap_on_memory, bool, 0444);
-MODULE_PARM_DESC(memmap_on_memory, "Enable memmap on memory for memory hotplug");
+enum {
+ MEMMAP_ON_MEMORY_DISABLE = 0,
+ MEMMAP_ON_MEMORY_ENABLE,
+ FORCE_MEMMAP_ON_MEMORY,
+};
+static int memmap_mode __read_mostly = MEMMAP_ON_MEMORY_DISABLE;
+static const char *memmap_on_memory_to_str[] = {
+ [MEMMAP_ON_MEMORY_DISABLE] = "disable",
+ [MEMMAP_ON_MEMORY_ENABLE] = "enable",
+ [FORCE_MEMMAP_ON_MEMORY] = "force",
+};
+
+static inline unsigned long memory_block_align_base(unsigned long size)
+{
+ if (memmap_mode == FORCE_MEMMAP_ON_MEMORY) {
+ unsigned long align;
+ unsigned long nr_vmemmap_pages = size >> PAGE_SHIFT;
+ unsigned long vmemmap_size;
+
+ vmemmap_size = DIV_ROUND_UP(nr_vmemmap_pages * sizeof(struct page), PAGE_SIZE);
+ align = pageblock_align(vmemmap_size) - vmemmap_size;
+ return align;
+ } else
+ return 0;
+}
+
+static int set_memmap_mode(const char *val, const struct kernel_param *kp)
+{
+ int ret = sysfs_match_string(memmap_on_memory_to_str, val);
+
+ if (ret < 0)
+ return ret;
+ *((int *)kp->arg) = ret;
+ if (ret == FORCE_MEMMAP_ON_MEMORY) {
+ pr_info("Memory hotplug will reserve %ld pages in each memory block\n",
+ memory_block_align_base(memory_block_size_bytes()));
+ }
+ return 0;
+}
+
+static int get_memmap_mode(char *buffer, const struct kernel_param *kp)
+{
+ return sprintf(buffer, "%s\n", memmap_on_memory_to_str[*((int *)kp->arg)]);
+}
+
+static const struct kernel_param_ops memmap_mode_ops = {
+ .set = set_memmap_mode,
+ .get = get_memmap_mode,
+};
+module_param_cb(memmap_on_memory, &memmap_mode_ops, &memmap_mode, 0644);
+MODULE_PARM_DESC(memmap_on_memory, "Enable memmap on memory for memory hotplug\n"
+ "With value \"force\" it could result in memory waste due to memmap size limitations \n"
+ "For example, if the memmap for a memory block requires 1 MiB, but the pageblock \n"
+ "size is 2 MiB, 1 MiB of hotplugged memory will be wasted. Note that there are \n"
+ "still cases where the feature cannot be enforced: for example, if the memmap is \n"
+ "smaller than a single page, or if the architecture does not support the forced \n"
+ "mode in all configurations. (disable/enable/force)");
static inline bool mhp_memmap_on_memory(void)
{
- return memmap_on_memory;
+ return !!memmap_mode;
}
#else
We can also enable runtime enable/disable/force the feature. We just
need to make sure on try_remove_memory we lookup for altmap correctly.
