On 02/06/2013 05:17 PM, Tang Chen wrote:
Hi all, On 02/06/2013 11:07 AM, Tang Chen wrote:Hi Glauber, all, An old thing I want to discuss with you. :) On 01/09/2013 11:09 PM, Glauber Costa wrote:memory can't be offlined when CONFIG_MEMCG is selected. For example: there is a memory device on node 1. The address range is [1G, 1.5G). You will find 4 new directories memory8, memory9, memory10, and memory11 under the directory /sys/devices/system/memory/. If CONFIG_MEMCG is selected, we will allocate memory to store page cgroup when we online pages. When we online memory8, the memory stored page cgroup is not provided by this memory device. But when we online memory9, the memory stored page cgroup may be provided by memory8. So we can't offline memory8 now. We should offline the memory in the reversed order. When the memory device is hotremoved, we will auto offline memory provided by this memory device. But we don't know which memory is onlined first, so offlining memory may fail. In such case, iterate twice to offline the memory. 1st iterate: offline every non primary memory block. 2nd iterate: offline primary (i.e. first added) memory block. This idea is suggested by KOSAKI Motohiro. Signed-off-by: Wen Congyang<wency@xxxxxxxxxxxxxx>Maybe there is something here that I am missing - I admit that I came late to this one, but this really sounds like a very ugly hack, that really has no place in here. Retrying, of course, may make sense, if we have reasonable belief that we may now succeed. If this is the case, you need to document - in the code - while is that. The memcg argument, however, doesn't really cut it. Why can't we make all page_cgroup allocations local to the node they are describing? If memcg is the culprit here, we should fix it, and not retry. If there is still any benefit in retrying, then we retry being very specific about why.We try to make all page_cgroup allocations local to the node they are describing now. If the memory is the first memory onlined in this node, we will allocate it from the other node. For example, node1 has 4 memory blocks: 8-11, and we online it from 8 to 11 1. memory block 8, page_cgroup allocations are in the other nodes 2. memory block 9, page_cgroup allocations are in memory block 8 So we should offline memory block 9 first. But we don't know in which order the user online the memory block. I think we can modify memcg like this: allocate the memory from the memory block they are describing I am not sure it is OK to do so.I don't see a reason why not. You would have to tweak a bit the lookup function for page_cgroup, but assuming you will always have the pfns and limits, it should be easy to do. I think the only tricky part is that today we have a single node_page_cgroup, and we would of course have to have one per memory block. My assumption is that the number of memory blocks is limited and likely not very big. So even a static array would do.About the idea "allocate the memory from the memory block they are describing", online_pages() |-->memory_notify(MEM_GOING_ONLINE, &arg) ----------- memory of this section is not in buddy yet. |-->page_cgroup_callback() |-->online_page_cgroup() |-->init_section_page_cgroup() |-->alloc_page_cgroup() --------- allocate page_cgroup from buddy system. When onlining pages, we allocate page_cgroup from buddy. And the being onlined pages are not in buddy yet. I think we can reserve some memory in the section for page_cgroup, and return all the rest to the buddy. But when the system is booting, start_kernel() |-->setup_arch() |-->mm_init() | |-->mem_init() | |-->numa_free_all_bootmem() -------------- all the pages are in buddy system. |-->page_cgroup_init() |-->init_section_page_cgroup() |-->alloc_page_cgroup() ------------------ I don't know how to reserve memory in each section. So any idea about how to deal with it when the system is booting please?How about this way. 1) Add a new flag PAGE_CGROUP_INFO, like SECTION_INFO and MIX_SECTION_INFO. 2) In sparse_init(), reserve some beginning pages of each section as bootmem.
Hi all, After digging into bootmem code, I met another problem.memblock allocates memory from high address to low address, using memblock.current_limit to remember where the upper limit is. What I am doing will produce a lot of fragments,
and the memory will be non-contiguous. So we need to modify memblock again. I don't think it's a good idea. How do you think ? Thanks. :)
3) In register_page_bootmem_info_section(), set these pages as page->lru.next = PAGE_CGROUP_INFO; Then these pages will not go to buddy system. But I do worry about the fragment problem because part of each section will be used in the very beginning. Thanks. :)And one more question, a memory section is 128MB in Linux. If we reserve part of the them for page_cgroup, then anyone who wants to allocate a contiguous memory larger than 128MB, it will fail, right ? Is it OK ? Thanks. :) -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html-- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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