Messages in this thread | | | Date | Fri, 30 Jan 2009 20:33:46 +0000 (GMT) | From | Hugh Dickins <> | Subject | Re: [PATCH] Fix OOPS in mmap_region() when merging adjacent VM_LOCKED file segments |
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On Fri, 30 Jan 2009, Lee Schermerhorn wrote: > > I tried this patch atop 29-rc3 + your patch from yesterday with my > simple test program at http://free.linux/hp.com/~lts/Tests/mmap_lock.c. > > The test program shows the /proc/<pid>/maps before and after the mmap > and attempted merge. It's not merging: > > 7fd20a668000-7fd20a66a000 rw-p 7fd20a668000 00:00 0 > 7fd20a68a000-7fd20a68b000 r--s 00000000 68:23 6608852 /tmp/tmpfVx1SFL (deleted) > 7fd20a68b000-7fd20a68c000 r--s 00001000 68:23 6608852 /tmp/tmpfVx1SFL (deleted) > 7fd20a68c000-7fd20a690000 rw-p 7fd20a68c000 00:00 0
Some testing - now that's a great idea! Good spotting.
> > Ad hoc instrumentation shows that it's the VM_ACCOUNT flag that is > different between the existing file segment and the one attempting the > merge: > > is_mergeable_vma: !mergable: vma flags: 0x80020f9:0x1020f9 > | |-VM_ACCOUNT > +-----------VM_CAN_NONLINEAR
Sorry, I should have noticed that: VM_ACCOUNT was certainly on my mind as a flag that gives trouble when merging vmas, but I'd misconvinced myself that it wasn't a problem in this case.
> > So happens, I'm mapping with MAP_SHARED, so the VM_ACCOUNT flag gets > cleared later in mmap_region(). Comments say that this is for checking > memory availability during shmem_file_setup(). Maybe we can move the > temporary setting of VM_ACCOUNT until just before the call to > shmem_zero_setup()?
Please let me think on that - we can live with the status quo for the moment. I need to remind myself why I used that peculiar way of conveying info from mmap.c to shmem.c: the right answer may be just to pass another arg to shmem_zero_setup and shmem_file_setup.
Hugh
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