On 21.07.2021 16:19, Andy Smith wrote: > On Wed, Jul 21, 2021 at 10:10:13AM +0200, Jan Beulich wrote: >> Since xen-blkback only talks in terms of bio-s, I don't think it is >> the party responsible for honoring such driver restrictions. Instead >> I'd expect the block layer's bio merging to be where this needs to be >> observed. Perhaps it simply doesn't expect to be passed requests in >> multiples of 11 sectors together with the capping at 64k (as said - >> iirc) and driver restrictions on where splits may occur? And as to >> earlier Linux versions working - perhaps the merging logic was less >> aggressive back then? > > I later realised that there was another change in my setup besides > the kernel version going from 4.19 to 5.10: I gave the dom0 8GiB of > memory instead of the 3GiB it had before. > > I understand that below 4GiB memory use of swiotlb is disabled so > all the time previously this was not used, and now is. Perhaps the > bug is in there? > > I was told that the only simple way on a Xen dom0 to disable use of > swiotlb would be to set the memory below 4GiB again, so I might try > that.
I have no idea where you take this 4GiB aspect from. What the kernel considers "below 4GiB" in its view of the world may be at a much higher address in system address space. And the mere amount of memory doesn't matter here at all. > I was also pointed to this patch as a maybe fix for my issue: > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=5f89468e2f060031cd89fd4287298e0eaf246bf6 Yes, this looks possibly related. Jan
