Messages in this thread |  | | Date | Tue, 14 May 2013 11:55:31 +0800 | From | Tang Chen <> | Subject | Re: [PATCH V2 1/2] mm: hotplug: implement non-movable version of get_user_pages() called get_user_pages_non_movable() |
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Hi Mel,
On 05/13/2013 05:19 PM, Mel Gorman wrote: >> For memory hot-remove case, the aio pages are pined in memory and making >> the pages cannot be offlined, furthermore, the pages cannot be removed. >> >> IIUC, you mean implement migrate_unpin() and migrate_pin() callbacks in aio >> subsystem, and call them when hot-remove code tries to offline >> pages, right ? >> >> If so, I'm wondering where should we put this callback pointers ? >> In struct page ? >> > > No, I would expect the callbacks to be part the address space operations > which can be found via page->mapping. >
Two more problems I don't quite understand.
1. For an anonymous page, it has no address_space, and no address space operation. But the aio ring problem just happened when dealing with anonymous pages. Please refer to: (https://lkml.org/lkml/2012/11/29/69)
If we put the the callbacks in page->mapping->a_ops, the anonymous pages won't be able to use them.
And we cannot give a default callback because the situation we are dealing with is a special situation.
So where to put the callback for anonymous pages ?
2. How to find out the reason why page->count != 1 in migrate_page_move_mapping() ?
In the problem we are dealing with, get_user_pages() is called to pin the pages in memory. And the pages are migratable. So we want to decrease the page->count.
But get_user_pages() is not the only reason leading to page->count increased. How can I know when should decrease teh page->count or when should not ?
The way I can figure out is to assign the callback pointer in get_user_pages() because it is get_user_pages() who pins the pages.
Thanks. :)
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