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由 Ken Chen 提交于
When kernel unmaps an address range, it needs to transfer PTE state into page struct. Currently, kernel transfer access bit via mark_page_accessed(). The call to mark_page_accessed in the unmap path doesn't look logically correct. At unmap time, calling mark_page_accessed will causes page LRU state to be bumped up one step closer to more recently used state. It is causing quite a bit headache in a scenario when a process creates a shmem segment, touch a whole bunch of pages, then unmaps it. The unmapping takes a long time because mark_page_accessed() will start moving pages from inactive to active list. I'm not too much concerned with moving the page from one list to another in LRU. Sooner or later it might be moved because of multiple mappings from various processes. But it just doesn't look logical that when user asks a range to be unmapped, it's his intention that the process is no longer interested in these pages. Moving those pages to active list (or bumping up a state towards more active) seems to be an over reaction. It also prolongs unmapping latency which is the core issue I'm trying to solve. As suggested by Peter, we should still preserve the info on pte young pages, but not more. Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: NKen Chen <kenchen@google.com> Cc: Hugh Dickins <hugh@veritas.com> Signed-off-by: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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