Messages in this thread |  | | | Date | Mon, 18 Jan 2010 21:35:12 +0800 | | From | Wu Fengguang <> | | Subject | Re: [PATCH 5/8] vmalloc: simplify vread()/vwrite() |
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On Thu, Jan 14, 2010 at 05:45:26AM -0700, Nick Piggin wrote: > On Wed, Jan 13, 2010 at 09:53:10PM +0800, Wu Fengguang wrote: > > vread()/vwrite() is only called from kcore/kmem to access one page at a time. > > So the logic can be vastly simplified. > > > > The changes are: > > - remove the vmlist walk and rely solely on vmalloc_to_page() > > - replace the VM_IOREMAP check with (page && page_is_ram(pfn)) > > - rename to vread_page()/vwrite_page() > > > > The page_is_ram() check is necessary because kmap_atomic() is not > > designed to work with non-RAM pages. > > I don't know if you can really do this. Previously vmlist_lock would be > taken, which will prevent these vm areas from being freed. > > > Note that even for a RAM page, we don't own the page, and cannot assume > > it's a _PAGE_CACHE_WB page. > > So why is this not a problem for your patch? I don't see how you handle > it.
Sorry I didn't handle it. Just hope to catch attentions from someone (ie. you :).
It's not a problem for x86_64 at all. For others I wonder if any driver will vmalloc HIGHMEM pages with !_PAGE_CACHE_WB attribute..
So I noted the possible problem and leave it alone.
> What's the problem with the current code, exactly? I would prefer that
- unnecessary complexity to handle multi-page case, since it's always called to access one single page;
- the kmap_atomic() cache consistency problem, which I expressed some concern (without further action)
> you continue using the same vmlist locking and checking for validating > addresses.
It's a reasonable suggestion. Kame, would you agree on killing the kmap_atomic() and revert to the vmlist walk?
Thanks, Fengguang
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