On Wed, Mar 18, 2020 at 02:29:17PM +0800, Feng Li wrote:
> Hi Ming,
> What I need is that always get contiguous pages in one bvec.
> Maybe currently it's hard to satisfy this requirement.
> About huge pages, I know the userspace processes could use huge pages
> that kernel reserved.
> Could bio/block layer support use huge pages?
Yes, you will see all pages in one huge page are stored in one single
bvec.
>
> Thanks again for your help.
>
> Ming Lei <ming.lei@xxxxxxxxxx> 于2020年3月17日周二 下午6:27写道：
>
> >
> > On Tue, Mar 17, 2020 at 04:19:44PM +0800, Feng Li wrote:
> > > Thanks.
> > > Sometimes when I observe multipage bvec on 5.3.7-301.fc31.x86_64.
> > > This log is from Qemu virtio-blk.
> > >
> > > ========= size: 262144, iovcnt: 2
> > > 0: size: 229376 addr: 0x7fff6a7c8000
> > > 1: size: 32768 addr: 0x7fff64c00000
> > > ========= size: 262144, iovcnt: 2
> > > 0: size: 229376 addr: 0x7fff6a7c8000
> > > 1: size: 32768 addr: 0x7fff64c00000
> >
> > Then it is working.
> >
> > >
> > > I also tested on 5.6.0-0.rc6.git0.1.vanilla.knurd.1.fc31.x86_64.
> > > And observe 64 iovcnt.
> > > ========= size: 262144, iovcnt: 64
> > > 0: size: 4096 addr: 0x7fffb5ece000
> > > 1: size: 4096 addr: 0x7fffb5ecd000
> > > ...
> > > 63: size: 4096 addr: 0x7fff8baec000
> > >
> > > So I think this is a common issue of the upstream kernel, from 5.3 to 5.6.
> >
> > As I mentioned before, it is because the pages aren't contiguous
> > physically.
> >
> > If you enable hugepage, you will see lot of pages in one single bvec.
> >
> > >
> > > BTW, I have used your script on 5.3.7-301.fc31.x86_64, it works well.
> > > However, when updating to kernel 5.6.0-0.rc6.git0.1.vanilla.knurd.1.fc31.x86_64.
> > > It complains:
> > >
> > > root@192.168.19.239 16:57:23 ~ $ ./bvec_avg_pages.py
> > > In file included from /virtual/main.c:2:
> > > In file included from
> > > /lib/modules/5.6.0-0.rc6.git0.1.vanilla.knurd.1.fc31.x86_64/build/include/uapi/linux/ptrace.h:142:
> > > In file included from
> > > /lib/modules/5.6.0-0.rc6.git0.1.vanilla.knurd.1.fc31.x86_64/build/arch/x86/include/asm/ptrace.h:5:
> > > /lib/modules/5.6.0-0.rc6.git0.1.vanilla.knurd.1.fc31.x86_64/build/arch/x86/include/asm/segment.h:266:2:
> > > error: expected '(' after 'asm'
> > > alternative_io ("lsl %[seg],%[p]",
> >
> > It can be workaround by commenting the following line in
> > /lib/modules/5.6.0-0.rc6.git0.1.vanilla.knurd.1.fc31.x86_64/build/include/generated/autoconf.h:
> >
> > #define CONFIG_CC_HAS_ASM_INLINE 1
> >
> >
> > Thanks,
> > Ming
> >
>
--
Ming
