Messages in this thread | | | Date | Mon, 10 Feb 2014 08:40:48 -0600 | From | Dave Kleikamp <> | Subject | Re: [PATCH 1/2] mm/vmalloc: export is_vmalloc_or_module_addr |
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On 02/10/2014 06:10 AM, Mel Gorman wrote: > On Sat, Feb 08, 2014 at 11:45:53AM -0800, Linus Torvalds wrote: >> On Sat, Feb 8, 2014 at 11:12 AM, Richard Yao <ryao@gentoo.org> wrote: >>> 9p-virtio needs is_vmalloc_or_module_addr exported before a patch can be >>> merged to prevent the virtio zero-copy routines from triggering a >>> hypervisor page fault when loading kernel modules: >>> >>> https://groups.google.com/forum/#!topic/linux.kernel/eRR7AyLE29Y >>> >>> Without this export, the kernel build breaks with that patch applied and >>> CONFIG_NET_9P_VIRTIO=m. With this export in place, all is well. >> >> I absolutely *detest* this patch. >> >> Not so much because is_vmalloc_or_module_addr() should never be used, >> but because the particular use in question is pure and utter garbage. >> >> There are valid reasons to use "is_vmalloc_or_module_addr()", but >> those are along the lines of drivers/char/mem.c, which says "return >> -ENXIO for this crap". >> >> And btw, that horrid crap called "kmap_to_page()" needs to die too. >> When is it *ever* valid to use a kmap'ed page for IO? Here's a clue: >> never. >> >> <SNIP> >> >> Those *disgusting* get_kernel_page[s]() functions came with a >> commentary about "The initial user is expected to be NFS.." and that >> is still the *only* user. The fact that *everybody* else has been able >> to avoid that crap should tell us something. > > kmap_to_page, get_kernel_page and the NFS user for it are already scheduled > for death. Dave Kleikamp has been working on a series "Issue O_DIRECT aio > using bio_vec" that replaces what NFS currently does with something far > more sane. The series does not remove the helpers on top, probably because > of the 9P use of it, but if that was changed then the helpers would finally > die. I'm not sure why Dave's series never got merged so added him to the > cc to find out.
The patchset I submitted was too ugly to live. Linus and Al Viro both had numerous issues with the implementation, but not the overall concept.
Al has the same idea for a io-vector container that can hold either an iovec or a kernel vector and is starting to work on his own implementation. Once he settles on the particulars of new aio_write/aio_read methods, I should be able to get the rest of my patchset to fall into line with it.
http://www.spinics.net/lists/linux-fsdevel/msg71938.html
Shaggy
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