Messages in this thread | | | Date | Fri, 14 Mar 2008 23:36:11 +0900 | From | Yasunori Goto <> | Subject | [PATCH 0/3 (RFC)](memory hotplug) freeing pages allocated by bootmem for hotremove |
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Hello.
I would like to post patch set to free pages which is allocated by bootmem for memory-hotremove.
Basic my idea is using remain members of struct page to remember information of users of bootmem (section number or node id). When the section is removing, kernel can confirm it. By this information, some issues can be solved.
1) When the memmap of removing section is allocated on other section by bootmem, it should/can be free. 2) When the memmap of removing section is allocated on the same section, it shouldn't be freed. Because the section has to be offlined already and all pages must be isolated against page allocater. Kernel keeps it as is. 3) When removing section has other section's memmap, kernel will be able to show easily which section should be removed before it for user. (Not implemented yet) 4) When the above case 2), the page migrator will be able to check and skip memmap againt page isolation when page offline. Current page migration fails in this case because this page is just reserved page and it can't distinguish this pages can be removed or not. But, it will be able to do by this patch. (Not implemented yet.) 5) The node information like pgdat has similar issues. But, this will be able to be solved too by this. (Not implemented yet, but, remembering node id in the pages.)
Fortunately, current bootmem allocator just keeps PageReserved flags, and doesn't use any other members of page struct. The users of bootmem doesn't use them too.
This patch set needs Badari-san's generic __remove_pages() support patch. http://linux.derkeiler.com/Mailing-Lists/Kernel/2008-03/msg02881.html
I think this patch set is not perfect. Because, some of section/node informations are smaller than one page, and bootmem allocator may mix other data. This patch is still trial. But I suppose this is good start for everyone to understand what is necessary.
Please comments.
Other Todo: - for SPARSEMEM_VMEMMAP. Freeing vmemmap's page is more diffcult than normal sparsemem. Because not only memmap's page, but also the pages like page table must be removed too. If removing section has pages for , then it must be migrated too. Relocatable page table is necessary.
- compile with other config. This version is just for requesting comments. If this way is accepted, I'll check it. - Follow fix bootmem by Yinghai Lu-san. (This patch set is for 2.6.25-rc3-mm1 with Badari-san's patch yet.)
Thanks.
-- Yasunori Goto
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