Messages in this thread |  | | | Date | Thu, 7 Jan 2010 11:57:36 +0900 | | From | KAMEZAWA Hiroyuki <> | | Subject | Re: [RFC][PATCH] vmalloc: simplify vread()/vwrite() |
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On Thu, 7 Jan 2010 10:50:54 +0800 Wu Fengguang <fengguang.wu@intel.com> wrote:
> > > 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)) > > > > > > The VM_IOREMAP check is introduced in commit d0107eb07320b for per-cpu > > > alloc. Kame, would you double check if this change is OK for that > > > purpose? > > > > > I think VM_IOREMAP is for avoiding access to device configuration area and > > unexpected breakage in device. Then, VM_IOREMAP are should be skipped by > > the caller. (My patch _just_ moves the avoidance of callers to vread()/vwrite()) > > "device configuration area" is not RAM, so testing of RAM would be > able to skip them? > Sorry, that's an area what I'm not sure. But, page_is_ram() implementation other than x86 seems not very safe... (And it seems that it's not defiend in some archs.)
> > > > > The page_is_ram() check is necessary because kmap_atomic() is not > > > designed to work with non-RAM pages. > > > > > I think page_is_ram() is not a complete method...on x86, it just check > > e820's memory range. checking VM_IOREMAP is better, I think. > > (double check) Not complete or not safe? > I think not-safe because e820 doesn't seem to be updated.
> EFI seems to not update e820 table by default. Ying, do you know why? >
I hope all this kinds can be fixed by kernel/resource.c in generic way.... Now, each archs have its own. > > > Even for a RAM page, we don't own the page, and cannot assume it's a > > > _PAGE_CACHE_WB page. So I wonder whether it's necessary to do another > > > patch to call reserve_memtype() before kmap_atomic() to ensure cache > > > consistency? > > > > > > TODO: update comments accordingly > > > > > > > BTW, f->f_pos problem on 64bit machine still exists and this patch is still > > hard to test. I stopped that because anyone doesn't show any interests. > > I'm using your patch :) > > I feel most inconfident on this patch, so submitted it for RFC first. > I'll then submit a full patch series including your f_pos fix. > Thank you, it's helpful.
Thanks, -Kame
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