Messages in this thread | | | Subject | Re: [PATCH] acquire mmap semaphore in pagemap_read. | From | Matt Mackall <> | Date | Tue, 17 Mar 2009 11:21:41 -0500 |
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On Tue, 2009-03-17 at 13:04 +0100, Martin Schwidefsky wrote: > On Thu, 12 Mar 2009 16:54:51 +0100 > Martin Schwidefsky <schwidefsky@de.ibm.com> wrote: > > > On Thu, 12 Mar 2009 10:23:34 -0500 > > Matt Mackall <mpm@selenic.com> wrote: > > > > > Well it means we may have to reintroduce the very annoying double > > > buffering from various earlier implementations. But let's leave this > > > discussion until after we've figured out what to do about the walker > > > code. > > > > About the walker code. I've realized that there is another way to fix > > this. The TASK_SIZE definition is currently used for two things: 1) as > > a maximum mappable address, 2) the size of the address space for a > > process. And there lies a problem: while a process is using a reduced > > page table 1) and 2) differ. If I make TASK_SIZE give you the current > > size of the address space then it is not possible to mmap an object > > beyond 4TB and the page table upgrade never happens. If I make > > TASK_SIZE return the maximum mappable address the page table walker > > breaks. The solution could be to introduce MAX_TASK_SIZE and use that > > in the mmap code to find out what can be mapped. > > I got around the TASK_SIZE checks with arch code only. In total I'll > need two fixes, one that makes TASK_SIZE to reflect the size of the > current address space and another one to get the page table upgrades > working again. I'll push these patches via git390 as no common code > changes are required.
Thanks, Martin.
> Which leaves the mmap_sem issue as the only problem left.
Yeah, this one needs more thought. I'd really rather not go back to double-buffering here as it was much more complicated, not to mention slow.
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