Re: [PATCH 3/4] mm: add shared read-only vmemmap support for FS-DAX

[Yilei Zheng]

Hi Muchun,

> Thank you very much for the test, so in your scenario, this is also
> the behavior of your real workload (mainly read/write-based, rather
> than mmap), right?

Yes. We mount read-only rootfs images over virtio-pmem and FS-DAX. Most
file access goes through normal read/write. mmap is only used for
loading binaries and shared libraries at startup, which is a small part
of the image.

> To be fair, it does fix the issue, but it's not very clean. I might
> do some code cleanup first to solve this more gracefully. I want to
> move the initialization to where the template page is allocated,
> similar to what section-based vmemmap optimization does.

Makes sense. Initializing it at allocation time is cleaner.

> Thanks for the analysis and suggestions. However, the reason I
> haven't sent out v2 yet is that I've been trying to refactor the
> vmemmap optimization logic to make FS_DAX support cleaner. I think
> I'll probably do some code refactoring first.

Understood. It would also help if the refactor could support subsection
(2 MiB) alignment, so any 2 MiB-aligned device can use the optimization
without padding to a 128 MiB multiple.

> I'cc you next time if you'd like to help me test.

Sounds good. Please Cc me when you post v2 and I'll be glad to test.

Best regards,
Yilei