On Sun, Sep 21, 2025 at 05:06:31PM +0530, Anshuman Khandual wrote:
>
>
> On 18/09/25 1:24 AM, Luck, Tony wrote:
> > On Wed, Sep 17, 2025 at 12:32:47PM -0700, Jiaqi Yan wrote:
> >> +1. Given /proc/sys/vm/enable_soft_offline is extensible, I would
> >> prefer a compact userspace API.
> >>
> >>> would create a new file, and the file has weird semantics such that it
> >>> has no meaning when enable_soft_offline=0.
> >
> > So the expand the bitmask idea from earlier in this thread?
> >
> > Bit0 0 = soft offline disabled. 1 = Enabled (but see other bits)
> > Bit1 0 = allow offline of 4K pages, 1 = suppress 4K offline
> > Bit2 0 = allow offline of hugetlb, 1 = suppress hugetlb offline
> > Bit3 0 = allow breakup of transparent huge pages to just offline 4K,
> > 1 = suppress transparent breakup
> > Bit4+ Reserved for suppressing other page types we invent in the
> > future
> >
> > Values 0 and 1 keep their original meaning.
> >
> > Value 5 means: offline 4K, keep hugetlb, breakup transparent huge pages.
>
> This disable bitmask (but when generally enabled via bit[0] = 1) method
> seems much better. But I am not sure about page size being a valid page
> type classification though. Just to start with, defining first two bits
> in this bitmask should be good enough, which will atleast help document
> and validate this new interface properly.
>
> Bit1 0 = allow offline of hugetlb, 1 = suppress hugetlb offline
> Bit2 0 = allow breakup of transparent huge pages to just offline base pages,
> 1 = suppress transparent breakup
> Bit3+ Reserved for suppressing other page types we invent in the future
The current patch is already applied to mm-git and supports the following bits:
0 - Enable soft offline
1 - Disable soft offline for HugeTLB pages
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/commit/?h=mm-new&id=9ae6eefa4b6bd3c3e7ef417a6507dce4b55101b4
Are any immediate changes needed?
Support for additional page types, such as transparent huge pages, can be added
later as needed.
Thanks,
Kyle Meyer
