Messages in this thread | | | Date | Tue, 22 Apr 2003 20:08:51 +0200 | From | Andrea Arcangeli <> | Subject | Re: objrmap and vmtruncate |
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On Tue, Apr 22, 2003 at 10:21:10AM -0700, William Lee Irwin III wrote: > On Tue, Apr 22, 2003 at 06:57:46PM +0200, Andrea Arcangeli wrote: > > could we focus and solve the remap_file_pages current breakage first? > > I proposed my fix that IMHO is optimal and simple (I recall Hugh also > > proposed something on these lines): > > 1) allow it only inside mmap(VM_NONLINAER) vmas only > > 2) have the VM skip over VM_NONLINEAR vmas enterely > > 3) set vma->vm_file to NULL for those vams and forbid paging and allow > > multiple files to be mapped in the same nonlinaer vma (add an fd > > parameter to the syscall) > > 4) enable it as non-root (w/o IPC_LOCK capability) only with a sysctl > > enabled > > 5) avoid any overhead connected with the potential paging of the > > nonlinaer vmas > > Some of these are controversial; it _can_ be fixed in other ways, but
which ones, could you elaborate? I don't see anything controversial in the above points.
> I'm trying to be objective here, though my own bias is in favor of full > retention of functionality (i.e. best of both worlds, maximal code > complexity).
I'm not at all against code complexity when it is worthwhile, but given the potential ram and cpu overhead of the complex code and considering this stuff should be ready in a few months I would prefer to keep things simple. Especially because if you really want, as said you could make things complex (and slower ;) behind this new API w/o userspace noticing. Then you can drop the sysctl (or make it insignificant).
> On Tue, Apr 22, 2003 at 06:57:46PM +0200, Andrea Arcangeli wrote: > > 6) populate it with pmd on hugetlbfs > > 7) if a truncate happens leave the page pinned outside the pagecache > > but still mapped into userspace, we don't care about it and it will > > be freed during the munmap of the nonlinear vma > > I'll implement the hugetlbfs part; it should fit nicely into the > infrastructure introduced with the rest of the virtwin patch, all it > really needs is some additional error checking. hugetlbfs is 100% > CAP_IPC_LOCK -- there should be no issue under either scheme.
yes.
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