Messages in this thread | | | Date | Thu, 05 Feb 2009 17:53:57 +0530 | From | Swamy Gowda <> | Subject | Re: [RFC][PATCH] release mmap_sem before starting migration (Was Re: Need to take mmap_sem lock in move_pages. |
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KAMEZAWA Hiroyuki wrote: > On Wed, 4 Feb 2009 10:39:19 -0500 (EST) > Christoph Lameter <cl@linux-foundation.org> wrote: > >> On Wed, 4 Feb 2009, KAMEZAWA Hiroyuki wrote: >> >> > mmap_sem can be released after page table walk ends. >> >> No. read lock on mmap_sem must be held since the migrate functions >> manipulate page table entries. Concurrent large scale changes to the >> page >> tables (splitting vmas, remapping etc) must not be possible. >> > Just for clarification: > > 1. changes in page table is not problem from the viewpoint of kernel. > (means no panic, no leak,...) > 2. But this loses "atomic" aspect of migration and will allow unexpected > behaviors. > (means the page-mapping status after sys_move may not be what user > expects.) > > > Thanks, > -Kame > > But I can't understand how user can see different page->mapping , since new page->mapping still holds the anon_vma pointer which should still contain the changes in the vma list( due to split vma etc). But, considering it as a problem how is it avoided in case of hotremove?
--Swamy
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