Messages in this thread | | | From | "Chen, Kenneth W" <> | Subject | RE: Hugepage regression | Date | Tue, 10 Oct 2006 12:30:07 -0700 |
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Hugh Dickins wrote on Tuesday, October 10, 2006 12:18 PM > On Tue, 10 Oct 2006, Chen, Kenneth W wrote: > > > > With the pending shared page table for hugetlb currently sitting in -mm, > > we serialize the all hugetlb unmap with a per file i_mmap_lock. This > > race could well be solved by that pending patch? > > > > http://kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.19-rc1/2.6.19-rc1-mm1/broken-out/shared-page-table-for-hugetlb-page-v 4.patch > > Hey, nice try, Ken! But I don't think we can let you sneak shared > pagetables into 2.6.19 that way ;)
It wasn't my intention to sneak in shared page table, though it does sort of look like so.
> Yes, I'd expect your i_mmap_lock to solve the problem: and since > you're headed in that direction anyway, it makes most sense to use > that solution rather than get into defining arrays, or sacrificing > the lazy flush, or risking page_count races. > > So please extract the __unmap_hugepage_range mods from your shared > pagetable patch, and use that to fix the bug.
OK, I was about to do so too.
> But again, I protest > the "if (vma->vm_file)" in your unmap_hugepage_range - how would a > hugepage area ever have NULL vma->vm_file?
It's coming from do_mmap_pgoff(), file->f_op->mmap can fail with error code (e.g. not enough hugetlb page) and in the error recovery path, it nulls out vma->vm_file first before calls down to unmap_region(). I asked that question before: can we reverse that order (call unmap_region and then nulls out vma->vmfile and fput)?
unmap_and_free_vma: if (correct_wcount) atomic_inc(&inode->i_writecount); vma->vm_file = NULL; fput(file);
/* Undo any partial mapping done by a device driver. */ unmap_region(mm, vma, prev, vma->vm_start, vma->vm_end);
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