Messages in this thread | | | Date | Sun, 4 Apr 2004 03:01:47 +0200 | From | Andrea Arcangeli <> | Subject | Re: anon-vma (and now filebacked-mappings too) mprotect vma merging [Re: 2.6.5-rc2-aa vma merging] |
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On Sat, Apr 03, 2004 at 08:29:15PM +0100, Hugh Dickins wrote: > I liked Andrew's vma->page_table_lock suggestion, was imagining we
vma->page_table_lock cannot help you with anonmm, the rbtree is global, for that you still need a mm-wide lock with anonmm. I serialize read/write the rbtree only with the mmap_sem, you cannot.
vma->page_table_lock helps _only_ in the pagetable scanning: so only _after_ nuking the global page_table_lock like I can do thanks to anon_vma. you cannot drop the mm-wide page_table_lock with anonmm. vma->page_table_lock is a natural optimization for the anon-vma logic instead (after fixing the mremap/truncate race ;).
To drop the page_table_lock during vma manipulations in anonmm (and so to give a real sense to a vma->page_table_lock in anonmm) you could use a down_read_trylock on the mm->mmap_sem, but that is not going to work well: the mmap_sem can be taken during extended period of times involving I/O, and you may never get it. BTW, now that the lookup on the prio-tree is immediate the i_shared_sem has no reason anymore to be a semaphore either, it should go back to a spinlock like in 2.4, like the anon_vma is also protected by a spinlock. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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